Books For Young Children

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Neutrinos produced by ultrahigh-energy photons at high red shift

Some of the proposed explanations for the origin of ultrahigh-energy cosmic rays invoke new sources of energetic photons (e.g., topological defects, relic particles, etc.). At high red shift, when the cosmic microwave background has a higher temperature but the radio background is low, the ultrahigh-energy photons can generate neutrinos through pair-production of muons and pions. Neutrinos produced at high red shift by slowly evolving sources can be detected. Rapidly evolving sources of photons can be ruled out based on the existing upper limit on the neutrino flux.Comment: 4 pages, revtex; to appear in Phys. Rev. Let

Predicting growth rates and recessions: assessing US leading indicators under real-time conditions

In this paper we analyze the power of various indicators to predict growth rates of aggregate production using real-time data. In addition, we assess their ability to predict turning points of the economy. We consider four groups of indicators: survey data, composite indicators, real economic indicators, and financial data. Almost all indicators are found to improve short-run growth forecasts whereas the results for four-quarter-ahead growth forecasts and the prediction of recession probabilities in general are mixed. We can confirm the result that an indicator suited to improve growth forecasts does not necessarily help to produce more accurate recession forecasts. Only composite leading indicators perform generally well in both forecasting exercises

A Latent Pro-survival Function for the Mir-290-295 Cluster in Mouse Embryonic Stem Cells

MicroRNAs (miRNAs) post-transcriptionally regulate the expression of thousands of distinct mRNAs. While some regulatory interactions help to maintain basal cellular functions, others are likely relevant in more specific settings, such as response to stress. Here we describe such a role for the mir-290-295 cluster, the dominant miRNA cluster in mouse embryonic stem cells (mESCs). Examination of a target list generated from bioinformatic prediction, as well as expression data following miRNA loss, revealed strong enrichment for apoptotic regulators, two of which we validated directly: Caspase 2, the most highly conserved mammalian caspase, and Ei24, a p53 transcriptional target. Consistent with these predictions, mESCs lacking miRNAs were more likely to initiate apoptosis following genotoxic exposure to gamma irradiation or doxorubicin. Knockdown of either candidate partially rescued this pro-apoptotic phenotype, as did transfection of members of the mir-290-295 cluster. These findings were recapitulated in a specific mir-290-295 deletion line, confirming that they reflect miRNA functions at physiological levels. In contrast to the basal regulatory roles previously identified, the pro-survival phenotype shown here may be most relevant to stressful gestations, where pro-oxidant metabolic states induce DNA damage. Similarly, this cluster may mediate chemotherapeutic resistance in a neoplastic context, making it a useful clinical target.National Institutes of Health (U.S.) (NIH grant RO1-GM34277)National Cancer Institute (U.S.) (NCI grant PO1-CA42063)National Cancer Institute (U.S.) (NCI Cancer Center Support (core) grant P30-CA14051

Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic

An evaluation of field methods of disease assessment in wheat (Triticum aestivum) for stripe rust (Puccinia striiformis)

The need to identify a simple but accurate method of stripe rust assessment that best predicts host response prompted this investigation. The study was divided into two plot types, one protected with the fungicide Bayleton and the other unprotected. Ten winter wheat cultivars were used and evaluated. Grain yield, test weight, kernels per spike and kernel weight were measured for each plot. Stripe rust severity was visually assessed at four different times according to the level of infection in the spreader row (a collection of cultivars susceptible to stripe rust). The four selected levels of infection were chosen based on the logarithmic increase in disease progression. The levels of infection (1-10%, 10-25%, 25-502 and 50-100%) were the four critical points chosen because of their placement along the disease progress curve. Several methods of disease assessment were compared and correlated with redacted kernel weight, which was used as a measure of yield loss. A coefficient of infection (CI) was used as the measure of disease assessment. The CI is calculated from the field readings by multiplying the percent severity by the value for infection type. A coefficient of infection was obtained for each plot at four specific dates. Disease levels in the unprotected plots and kernel weights were compared for each time of observation and correlations were determined. The data showed that the single visual assessment showing the highest correlation of all assessments compared in the study as they related to reduced kernel weight (r - =.791) was the third observation recorded as a coefficient of infection on May 30 when the level of infection in the spreader row was 25 to 50 percent or when the stripe rust epidemic was increasing logarithmically or in the logistic phase. Two other methods of assessment found less effective were analyzed using a transformed value for percent severity. Disease severity is usually measured on a logarithmic scale but for this computation, an arithmetic value for percent severity was used. When this value was included in determination of a coefficient of infection, there were lower r values associated with kernel weight than when the untransformed values for percent severity were used. The second additional assessment method utilized only the transformed percent severity reading to measure the amount of disease present with no regard to infection type. The correlations with these observations were also extremely low. Finally the area under the disease progress curves (AUDPC) were measured for the unprotected plots and correlated with kernel weight. When all ten cultivars were averaged and AUDPCs and kernel weights correlated, an r value of -.505 was obtained. Evidence provided in this study supports the use of a critical point model in that a single visual assessment of stripe rust was identified to estimate loss. AUDPCs were found to most accurately reflect host response to the presence of stripe rust infection. The strategy of an assessment program must be adapted to the characteristics of the pathogen under investigation and to the breeding program in which it will be implemented

Temporal Transcriptional Profiling of Somatic and Germ Cells Reveals Biased Lineage Priming of Sexual Fate in the Fetal Mouse Gonad

The divergence of distinct cell populations from multipotent progenitors is poorly understood, particularly in vivo. The gonad is an ideal place to study this process, because it originates as a bipotential primordium where multiple distinct lineages acquire sex-specific fates as the organ differentiates as a testis or an ovary. To gain a more detailed understanding of the process of gonadal differentiation at the level of the individual cell populations, we conducted microarrays on sorted cells from XX and XY mouse gonads at three time points spanning the period when the gonadal cells transition from sexually undifferentiated progenitors to their respective sex-specific fates. We analyzed supporting cells, interstitial/stromal cells, germ cells, and endothelial cells. This work identified genes specifically depleted and enriched in each lineage as it underwent sex-specific differentiation. We determined that the sexually undifferentiated germ cell and supporting cell progenitors showed lineage priming. We found that germ cell progenitors were primed with a bias toward the male fate. In contrast, supporting cells were primed with a female bias, indicative of the robust repression program involved in the commitment to XY supporting cell fate. This study provides a molecular explanation reconciling the female default and balanced models of sex determination and represents a rich resource for the field. More importantly, it yields new insights into the mechanisms by which different cell types in a single organ adopt their respective fates

Reconnecting a Stream Channel to its Floodplain: implications for benthic diatoms and macroinvertebrate trophic structure

Streams systems draining upland landscapes provide valuable ecosystem services, but they are vulnerable to incision and channelization caused by anthropogenic disturbance. Restoring a degraded stream to its pre-disturbance condition by reconnecting the channel to its historical floodplain aims to recover lost hydro-morphological processes and functions. Seeking evidence to indicate whether that aim is met in practice, we examined diatoms and the stream macroinvertebrate trophic structures in three reaches of Whychus Creek, Oregon, United States. Two reaches were reconnected to their pre-disturbance floodplains in 2012 and 2016. The third, control reach, was not restored and was selected to represent the degraded stream condition prior to restoration. Ordinations showed that benthic diatom species composition shifted from the control reach to the restored reaches. Compared to the control reach, reconnection decreased the percentages of diatoms with nitrogen (N)-fixing cyanobacterial endosymbionts in the 2012 restored reach and decreased diatoms tolerant to low N conditions in both the restored reaches. δ15N values in both stream macroinvertebrates and tree leaves in the riparian zone were higher in the restored reaches. These findings suggest that floodplain reconnection may modify hydro-morphological processes and ecosystem functions in ways that enhance organic matter retention and hyporheic exchange, resulting in increased nutrient availability, improved nutrient cycling, and greater primary productivity. More generally, our results suggest that characterizing diatom species composition and trophic interactions using stable isotopes provides the basis for identifying and evaluating the beneficial effects of stream restoration on ecosystem functions and the food-web