The average GeV-band Emission from Gamma-Ray Bursts

We analyze the emission in the 0.3-30 GeV energy range of Gamma-Ray Bursts detected with the Fermi Gamma-ray Space Telescope. We concentrate on bursts that were previously only detected with the Gamma-Ray Burst Monitor in the keV energy range. These bursts will then be compared to the bursts that were individually detected with the Large Area Telescope at higher energies. To estimate the emission of faint GRBs we use non-standard analysis methods and sum over many GRBs to find an average signal which is significantly above background level. We use a subsample of 99 GRBs listed in the Burst Catalog from the first two years of observation. Although mostly not individually detectable, the bursts not detected by the Large Area Telescope on average emit a significant flux in the energy range from 0.3 GeV to 30 GeV, but their cumulative energy fluence is only 8% of that of all GRBs. Likewise, the GeV-to-MeV flux ratio is less and the GeV-band spectra are softer. We confirm that the GeV-band emission lasts much longer than the emission found in the keV energy range. The average allsky energy flux from GRBs in the GeV band is 6.4*10^-4 erg cm^-2 yr^-1 or only 4% of the energy flux of cosmic rays above the ankle at 10^18.6 eV.Comment: Astronomy and Astrophysics, version accepted for publicatio

Optical characteristics of Nd:YAG optics and distortions at high power

The intensity profile and beam caustics of a fiber coupled high power Nd:YAG laser beam through a lens system are studied. The thermal lensing effect and its influence on the beam profile and focal position are discussed. Asymmetry of the intensity profile in planes above and below the focal plane is demonstrated. Also the influence of small pollutions on the protective window is explained. Three different methods are used to measure the occurrence\ud of thermal lensing and quantify these effects

NAUTILUS: boosting Bayesian importance nested sampling with deep learning

We introduce a novel approach to boost the efficiency of the importance nested sampling (INS) technique for Bayesian posterior and evidence estimation using deep learning. Unlike rejection-based sampling methods such as vanilla nested sampling (NS) or Markov chain Monte Carlo (MCMC) algorithms, importance sampling techniques can use all likelihood evaluations for posterior and evidence estimation. However, for efficient importance sampling, one needs proposal distributions that closely mimic the posterior distributions. We show how to combine INS with deep learning via neural network regression to accomplish this task. We also introduce NAUTILUS, a reference open-source Python implementation of this technique for Bayesian posterior and evidence estimation. We compare NAUTILUS against popular NS and MCMC packages, including EMCEE, DYNESTY, ULTRANEST and POCOMC, on a variety of challenging synthetic problems and real-world applications in exoplanet detection, galaxy SED fitting and cosmology. In all applications, the sampling efficiency of NAUTILUS is substantially higher than that of all other samplers, often by more than an order of magnitude. Simultaneously, NAUTILUS delivers highly accurate results and needs fewer likelihood evaluations than all other samplers tested. We also show that NAUTILUS has good scaling with the dimensionality of the likelihood and is easily parallelizable to many CPUs.Comment: 15 pages, 10 figures, submitted to MNRAS; code available at https://github.com/johannesulf/nautilu

Distribution Matching : Semi-Supervised Feature Selection for Biased Labelled Data

In the context of data science and machine learning, feature selection is a widely used technique that focuses on reducing the dimensionality of a dataset. It is commonly used to improve model accuracy by preventing data redundancy and over-fitting, but can also be beneficial in applications such as data compression. The majority of feature selection techniques rely on labelled data. In many real-world scenarios, however, data is only partially labelled and thus requires so-called semi-supervised techniques, which can utilise both labelled and unlabelled data. While unlabelled data is often obtainable in abundance, labelled datasets are smaller and potentially biased. This thesis presents a method called distribution matching, which offers a way to do feature selection in a semi-supervised setup. Distribution matching is a wrapper method, which trains models to select features that best affect model accuracy. It addresses the problem of biased labelled data directly by incorporating unlabelled data into a cost function which approximates expected loss on unseen data. In experiments, the method is shown to successfully minimise the expected loss transparently on a synthetic dataset. Additionally, a comparison with related methods is performed on a more complex EMNIST dataset

Magneto-optic Kerr effect of strongly correlated electron compounds

The optical conductivity and the magneto-optic polar Kerr effect of RAl 2 (R = La, Ce, Pr), RFe2 (R = Y, Ce), RNi 2B2C (R = Tm, Yb), CeB6, and YbBiPt were measured between 1.4 and 5.4 eV using a rotating analyzer ellipsometer and a normal incidence Kerr spectrometer. Optical absorption of RAl2, RFe 2, and RNi2B2C shows metallic behavior. For the low carrier concentration metals CeB6 and YbBiPt the spectrum is dominated by interband transitions. Spectra of RAl2 and RFe 2 show absorption at 2 eV which is also found in heavier RFe2 compounds. This structure is attributed to R-derived transitions. At higher energy transitions are governed by Fe-derived states. Alloying CeFe2 with 10% Co leads to a magnetic instability with a low-temperature antiferromagnetic ground state. The metamagnetic transition to the field-induced ferromagnetic state was observed using the Kerr effect. We measured the Kerr rotation at 1.8 and 4 eV across this transition, which occurs between 35 and 40 kOe at 50 K. For the magnetic superconductor TmNi2B2C the transition from the superconducting to the normal state was found in the Kerr rotation. A critical field of 10 kOe was estimated, which is in excellent agreement with the value derived from magnetization data. CeB6 shows a peak in the Kerr effect, which coincides with the plasma edge at 2 eV. No such feature was found in YbBiPt. The plasma edge appears to be screened by interband transitions;We used the tight-binding linear muffin-tin orbital method to calculate the band structure and density of states. The spin magnetic moment obtained by the local density approximation (LDA) is generally in good agreement with experiment. The orbital moment of localized states is overestimated by LDA. For the more itinerant 4f states found in CeFe2 the magnetic moments predicted by LDA are close to the experimentally observed moments. The optical conductivity for LaAl2 and YFe2 agrees well with the one measured. LDA does not reproduce the conductivity for the other compounds, which we attribute to an inadequate treatment of the localized 4f states in the LDA. Spectra were analyzed using band structure plots which included the orbital character of the bands

Effects of drought and the role of auxin on barley stamen maturation

Drought is a major abiotic stress that reduces crop yields all over the world. Climate change is predicted to increase the frequency and intensity of future drought events. Concomitantly, the increasing world population will require a rise in global crop production. To prevent a severe food insecurity situation, it is a pressing need to create varieties with robust yields under water deficit conditions, in economically important crops such as barley. Drought stress, occurring during the phase shortly before anthesis, is especially harmful to male reproductive development, which takes place in the stamens. Thus, understanding the molecular aspects that are essential for stamen development and that are also disrupted by drought stress should provide basis for targeted crop improvement. First, this work investigated the effects of transient drought stress on barley stamen development during the post-meiotic maturation phase. Drought treatment started around the phase of microspore release caused the highest reduction in barley spikelet fertility and was mainly caused by impaired male fertility, although female organ development was also negatively affected. Stamens that showed an altered morphology upon drought harbored viable but starch-less and infertile pollen. Accordingly, transcriptome analysis of stamens revealed that drought downregulates genes involved in central carbon metabolism, ranging from sucrose degradation to ATP synthesis, and in starch metabolism. Furthermore, drought-stressed stamens contained reduced levels of sucrose, hexoses and succinate. Drought also downregulated the expression of genes related to auxin synthesis, response and signaling in stamens. Thus, this work supports that auxin upregulates central carbon metabolism to ensure pollen starch accumulation, hence male fertility. Therefore, controlling auxin response and signaling in stamens may offer a valuable approach to improve pollen maturation and yield under drought. Moreover, screening of a subset of the wild barley introgression line population S42IL and the genotypes Golden Promise Fast (GPF) and GB2 identified potential drought-tolerant accessions that could serve as genetic resources in future crop improvement programs. Next, comparative omics analyses between stamens of the auxin-deficient mutant male sterile genetic 38 (msg38) and the fertile cultivar Bowman were conducted to study the role of auxin in barley stamen maturation, with a special focus on auxin response and central carbon metabolism factors. Transcriptome analysis indicated that auxin predominantly regulates primary targets of auxin signaling at early stages of stamen maturation. However, auxin extensively regulates gene expression during the phase of pollen starch accumulation, particularly boosting genes related to energy production. Decreased expression of auxin-dependent energy production genes in msg38 stamens often correlated well with lower levels of the corresponding proteins. Moreover, auxin was found to control the phosphorylation of sugar utilization enzymes and other factors of energy generation. These findings underline the importance of auxin as major regulator of the stamen energy production pathway. In sum, this work provides a basis for future analysis of the auxin signaling cascade as well as targeted molecular engineering in stamens that could help to improve male fertility under adverse environmental conditions such as drought

CRISPR Gene Editing Drivers, Barriers and Prospects: A Comparative Study among Plant Scientists Globally

The introduction of CRISPR gene editing into food crops has potential to contribute to food security and sustainable food production globally. To date, most scientific studies have focused on consumer perception of CRISPR gene edited foods or the potential benefits and risks of the CRISPR technology and none have focused on the perceptions of plant scientists concerning CRISPR gene editing. This study aimed to explore the investments, functions, barriers, benefits for specific crops and beneficiaries of CRISPR gene editing according to plant scientists, by distributing an online survey in which 1,040 plant scientists active across six continents and in both the public and private sector participated. By asking the respondents the current (and envisioned future) percentage of the total research and development that is spend on CRISPR gene editing, we found that relative investments in CRISPR gene editing are expected to increase in the next ten years in all continents and in both the public and private sector. Moreover, plant scientists expect that fungus resistance and virus resistance are the functions most likely to be implemented using CRISPR technology. Consumer perceptions/knowledge gap and policy/legal issues were perceived as the most impeding barriers of CRISPR adoption globally, where intellectual property rights issues are a major impediment in high-income countries and high development costs in low-income countries. Maize and soybean are expected to benefit the most from CRISPR gene editing across all regions, except for Oceania. Wheat, rice and potatoes are other crops in which plant scientists see potential to benefit from the CRISPR technology. Increased yields are expected to be the biggest beneficiary of CRISPR gene editing, where public scientists also see producer profits as an important beneficiary of the technology. Importantly, plant scientists are reluctant to the idea of CRISPR gene editing being regulated in a similar way as GM crops and expect the private sector to dominate the CRISPR market. The consensus among plant scientists is that CRISPR technology can contribute significantly to the enhancement of environmental sustainability and food insecurity issues