Big Bang nucleosynthesis revisited via Trojan Horse Method measurements

Nuclear reaction rates are among the most important input for understanding the primordial nucleosynthesis and therefore for a quantitative description of the early Universe. An up-to-date compilation of direct cross sections of 2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given. These are among the most uncertain cross sections used and input for Big Bang nucleosynthesis calculations. Their measurements through the Trojan Horse Method (THM) are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the 2H, 3,4He and 7Li primordial abundances, which are then compared with observations.Comment: 22 pages, 7 figures, accepted for publication in The Astrophysical Journa

MetaEnhance: Metadata Quality Improvement for Electronic Theses and Dissertations

Metadata quality is crucial for digital objects to be discovered through digital library interfaces. Although DL systems have adopted Dublin Core to standardize metadata formats (e.g., ETD-MS v1.11), the metadata of digital objects may contain incomplete, inconsistent, and incorrect values [1]. Most existing frameworks to improve metadata quality rely on crowdsourced correction approaches, e.g., [2]. Such methods are usually slow and biased toward documents that are more discoverable by users. Artificial intelligence (AI) based methods can be adopted to overcome this limit by automatically detecting, correcting, and canonicalizing the metadata, featuring quick and unbiased responses to document metadata. This paper uses Electronic Theses and Dissertations (ETDs) metadata as a case study and proposes an AI-based framework to improve metadata quality. ETD represents scholarly works of students who pursue higher education and successfully meet the partial requirement of a degree. ETDs are usually hosted by university libraries or ProQuest. Using web crawling techniques, we collected metadata and full text of 533,047 ETDs from 114 American universities. Upon inspecting the metadata of these ETDs, we noticed many ETD repositories are accompanied by incomplete, inconsistent, or incorrect metadata. We propose MetaEnhance, a framework that utilizes state-of-the-art AI methods to improve the quality of seven key metadata fields, including title, author, university, year, degree, advisor, and department. To evaluate MetaEnhance, we compiled a benchmark containing 500 ETDs, by combining subsets sampled using different criteria. We evaluated MetaEnhance against this benchmark and found that the proposed methods achieved remarkable performance in detecting and correcting metadata errors.https://digitalcommons.odu.edu/gradposters2023_sciences/1013/thumbnail.jp

Spray Freeze Drying as a Smart Method in Preparation of Ultra-Fine CeO2-MOX Materials

Cerium-oxide based nano-materials attract increasing interest for their use in multiple applications. In particular, the substitution of Ce atoms by other elements with lower or higher oxidation state is used to control oxygen vacancies within the oxide structures, which can greatly enhance the material properties for catalysis applications. Among the synthesis approaches, spray freeze drying method has been proved to be an extremely efficient method for the preparation of uniform nano-partical for different application. In this method, the pure solution or mixed solutions were directly sprayed into liquid nitrogen and immediately frozen to form a suspension, then, the iced droplets were dried in the freeze-dryer to reach the final product. However, in this work we deal with, the preparation of ultra-fine materials based on CeO2 fluorite structures and the substitution in its lattice with La and/or Co metal. The effect of Ce/La ratio on the properties of the final product was also investigated. During the experiment, the advantage of spray-freeze-drying process was successfully achieved. The characterization of the powder product was analyzed by means of EDX, TGA, XRD, DLS, and TEM which confirm the formation of nano-particles in the fluorite structure. For Ce:Co and when the Ce: La ratio is 0.2, 0.5, only cubic phase of CeO2-MO2 solid solution with ?uorite structure is observed with hig oxygen storage capacity, while Ce-La1 show the hcp structure of lanthanum. Keywords: nano-materials, Ceria, Lanthanium, metal loading spray freeze dryin

nuclear physics and its role for describing the early universe

Big Bang Nucleosynthesis (BBN) requires several nuclear physics inputs and nuclear reaction rates. An up-to-date compilation of direct cross sections of [Formula: see text], [Formula: see text]He and [Formula: see text]He reactions is given, being these ones among the most uncertain bare-nucleus cross sections. An intense experimental effort has been carried on in the last decade to apply the Trojan Horse Method (THM) to study reactions of relevance for the BBN and measure their astrophysical S(E)-factor. The reaction rates and the relative error for the four reactions of interest are then numerically calculated in the temperature ranges of relevance for BBN [Formula: see text]. These value were then used as input physics for primordial nucleosynthesis calculations in order to evaluate their impact on the calculated primordial abundances and isotopical composition for H, He and Li. New results on the [Formula: see text]He reaction rate were also taken into account.These were compared with the observational primordial abundance estimates in different astrophysical sites. Reactions to be studied in perspective will also be discussed

ASTROPHYSICAL IMPACT of the UPDATED 9Be(p,)6Li and 10B(p,)7Be REACTION RATES AS DEDUCED by THM

The complete understanding of the stellar abundances of lithium, beryllium, and boron represents one of the most interesting open problems in astrophysics. These elements are largely used to probe stellar structure and mixing phenomena in different astrophysical scenarios, such as pre-main-sequence or main-sequence stars. Their different fragility against (p,) burning reactions allows one to investigate different depths of the stellar interior. Such fusion mechanisms are triggered at temperatures between T ≈ (2-5) × K, thus defining a corresponding Gamow energy between ≈ 3-10 keV, where S(E)-factor measurements need to be performed to get reliable reaction rate evaluations. The Trojan Horse Method is a well defined procedure to measure cross sections at Gamow energies overcoming the uncertainties due to low-energy S(E)-factor extrapolation as well as electron screening effects. Taking advantage of the measure of the 9Be(p,)6Li and 10B(p,)7Be cross sections, the corresponding reaction rates have been calculated and compared with the evaluations by the NACRE collaboration, widely used in the literature. The impact on surface abundances of the updated 9Be and 10B (p,) burning rates is discussed for pre-MS stars

Solving the large discrepancy between inclusive and exclusive measurements of the 8Li+4He→11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n reaction cross section at astrophysical energies

A solution of the large discrepancy existing between inclusive and exclusive measurements of the ${}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n$ reaction cross section at $E_{cm} <3$ MeV is evaluated. This problem has profound astrophysical relevance for this reaction is of great interest in Big-Bang and r-process nucleosynthesis. By means of a novel technique, a comprehensive study of all existing ${}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n$ cross section data is carried out, setting up a consistent picture in which all the inclusive measurements provide the reliable value of the cross section. New unambiguous signatures of the strong branch pattern non-uniformities, near the threshold of higher ${}^{11}{\rm B}$ excited levels, are presented and their possible origin, in terms of the cluster structure of the involved excited states of ${}^{11}{\rm B}$ and ${}^{12}{\rm B}$ nuclei, is discussed.Comment: 5 pages, 4 figures, 1 tabl

Identification of the direct regulon of NtcA during early acclimation to nitrogen starvation in the cyanobacterium Synechocystis sp. PCC 6803

In cyanobacteria, nitrogen homeostasis is maintained by an intricate regulatory network around transcription factor NtcA. Although mechanisms controlling NtcA activity appear to be well understood, its regulon remains poorly defined. To determine the NtcA regulon during the early stages of nitrogen starvation for the model cyanobacterium Synechocystis sp. PCC 6803, we performed chromatin immunoprecipitation, followed by sequencing (ChIP-seq), in parallel with transcriptome analysis (RNA-seq). Through combining these methods, we determined 51 genes activated and 28 repressed directly by NtcA. In addition to genes associated with nitrogen and carbon metabolism, a considerable number of genes without current functional annotation were among direct targets providing a rich reservoir for further studies. The NtcA regulon also included eight non-coding RNAs, of which Ncr1071, Syr6 and NsiR7 were experimentally validated, and their putative targets were computationally predicted. Surprisingly, we found substantial NtcA binding associated with delayed expression changes indicating that NtcA can reside in a poised state controlled by other factors. Indeed, a role of PipX as modulating factor in nitrogen regulation was confirmed for selected NtcA-targets. We suggest that the indicated poised state of NtcA enables a more differentiated response to nitrogen limitation and can be advantageous in native habitats of Synechocystis.Ministerio de Economia y Competitividad (MINECO) [BFU2013-41712, BIO2016-75634]; Junta de Andalucia-European Regional Funds (FEDER) [BIO-284, P12-BIO-1119]; FCT (Fundacao para a Ciencia e a Tecnologia) [PTDC/BIA-MIC/4418/2012, IF/00881/2013, UID/BIM/04773/2013-CBMR, UID/Multi/04326/2013-CCMAR]; School of Biomedical & Healthcare Sciences, Plymouth University Peninsula Schools of Medicine and Dentistryinfo:eu-repo/semantics/publishedVersio

Measurement of the 20 and 90 keV resonances in the 18O(p,α)15{}^{18}{\rm O}(p,\alpha){}^{15}N reaction via THM

The $^{18}{\rm O}(p,\alpha)^{15}{\rm N}$ reaction is of primary importance in several astrophysical scenarios, including fluorine nucleosynthesis inside AGB stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus the indirect measurement of the low energy region of the $^{18}{\rm O}(p,\alpha)^{15}{\rm N}$ reaction has been performed to reduce the nuclear uncertainty on theoretical predictions. In particular the strength of the 20 and 90 keV resonances have been deduced and the change in the reaction rate evaluated.Comment: 4 pages, 4 figures, submitted to PR