Modeling the sorption dynamics of NaH using a reactive force field

We have parametrized a reactive force field for NaH, ReaxFFNaH, against a training set of ab initio derived data. To ascertain that ReaxFFNaH is properly parametrized, a comparison between ab initio heats of formation of small representative NaH clusters with ReaxFFNaH was done. The results and trend of ReaxFFNaH are found to be consistent with ab initio values. Further validation includes comparing the equations of state of condensed phases of Na and NaH as calculated from ab initio and ReaxFFNaH. There is a good match between the two results, showing that ReaxFFNaH is correctly parametrized by the ab initio training set. ReaxFFNaH has been used to study the dynamics of hydrogen desorption in NaH particles. We find that ReaxFFNaH properly describes the surface molecular hydrogen charge transfer during the abstraction process. Results on heat of desorption versus cluster size shows that there is a strong dependence on the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. To gain more insight into the structural transformations of NaH during thermal decomposition, we performed a heating run in a molecular dynamics simulation. These runs exhibit a series of drops in potential energy, associated with cluster fragmentation and desorption of molecular hydrogen. This is consistent with experimental evidence that NaH dissociates at its melting point into smaller fragments

Color stability of sorghum 3-deoxyanthocyanins against sulfite and ascorbic acid degradation: pH influence

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on November 11, 2008)Includes bibliographical references.Thesis (M.S.) University of Missouri-Columbia 2007.Dissertations, Academic -- University of Missouri--Columbia -- Food science.The degradation of anthocyanins by food additives like SO2 and ascorbic acid limits their use as natural food colorants. The rare 3-deoxyanthocyanins from sorghum are relatively stable compared to other anthocyanins, but have not been investigated. The stability of 3-deoxyanthocyanin standards, red cabbage pigment, grape blue powder and crude sorghum pigment extract against SO2, ascorbic acid bleaching and high temperature treatment (121.1⁰C for 15 min) at pH 2.0, 3.0, 3.2 and 5.0 was measured in the presence (50:1 molar ratio) or absence of pyruvic acid. Samples were incubated at 37⁰C for 5 days to synthesize the pyruvic acid adducts, and their sulfite and ascorbic acid bleaching resistance investigated at 60 ppm and 500 ppm respectively, using a Shimadzu UV-1650PC spectrophotometer for 21 days. HPLC-DAD/MS analysis confirmed the formation of the 3-deoxyanthocyanin-pyruvic acid adducts at approximately 11 - 47% conversion. Samples without pyruvic acid were the controls. Sulfite and ascorbic acid are co-pigments with 3-deoxyanthocyanin pigments in absence of pyruvic acid at pH 2.0 and 5.0, respectively. Pyruvic acid had marginal protective influence on the stability of the pigments against sulfite and ascorbic acid degradation but not heat. Crude black sorghum extract was the most stable to SO2 and ascorbic acid bleaching. High temperature initiated production of new 3-deoxyanthocyanin-pyruvic acid adducts

Parametrization of a reactive force field for aluminum hydride

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFF_(AlH_3) is used to study the dynamics governing hydrogen desorption in AlH_3. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFF_(AlH_3). Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH_4

Multiscale modeling of interaction of alane clusters on Al(111) surfaces: A reactive force field and infrared absorption spectroscopy approach

We have used reactive force field (ReaxFF) to investigate the mechanism of interaction of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. In addition, from our simulations, adsorption of atomic hydrogen on Al(111) surface leads to the formation of alanes via H-induced etching of aluminum atoms from the surface. The alanes then agglomerate at the step edges forming stringlike conformations. The identification of these stringlike intermediates as a precursor to the bulk hydride phase allows us to explain the loss of resolution in surface IR experiments with increasing hydrogen coverage on single crystal Al(111) surface. This is in excellent agreement with the experimental works of Go et al. [ E. Go, K. Thuermer, and J. E. Reutt-Robey, Surf. Sci. 437, 377 (1999) ]. The mobility of alanes molecules has been studied using molecular dynamics and it is found that the migration energy barrier of Al_(2)H_6 is 2.99 kcal/mol while the prefactor is D_0 = 2.82 × 10^(−3) cm^2/s. We further investigated the interaction between an alane and an aluminum vacancy using classical molecular dynamics simulations. We found that a vacancy acts as a trap for alane, and eventually fractionates/annihilates it. These results show that ReaxFF can be used, in conjunction with ab initio methods, to study complex reactions on surfaces at both ambient and elevated temperature conditions

Modeling of Hydrogen Storage Materials: A Reactive Force Field for NaH

Parameterization of a reactive force field for NaH is done using ab initio derived data. The parameterized force field(ReaxFFNaH) is used to study the dynamics governing hydrogen desorption in NaH. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by the parameterized force field. To gain more insight into the mechanism governing structural transformation of NaH during thermal decomposition a heating run in a molecular dynamics simulation is done. The result shows that a clear signature of hydrogen desorption is the fall in potential energy surface during heating

Predictions of melting, crystallization, and local atomic arrangements of aluminum clusters using a reactive force field

A parametrized reactive force field model for aluminum ReaxFFAl has been developed based on density functional theory (DFT) data. A comparison has been made between DFT and ReaxFFAl outputs to ascertain whether ReaxFFAl is properly parametrized and to check if the output of the latter has correlation with DFT results. Further checks include comparing the equations of state of condensed phases of Al as calculated from DFT and ReaxFFAl. There is a good match between the two results, again showing that ReaxFFAl is correctly parametrized as per the DFT input. Simulated annealing has been performed on aluminum clusters Aln using ReaxFFAl to find the stable isomers of the clusters. A plot of stability function versus cluster size shows the existence of highly stable clusters (magic clusters). Quantum mechanically these magic clusters arise due to the complete filling of the orbital shells. However, since force fields do not care about electrons but work on the assumption of validity of Born–Oppenheimer approximation, the magic clusters are therefore correlated with high structural symmetry. There is a rapid decline in surface energy contribution due to the triangulated nature of the surface atoms leading to higher coordination number. The bulk binding energy is computed to be 76.8 kcal/mol. This gives confidence in the suitability of ReaxFF for studying and understanding the underlying dynamics in aluminum clusters. In the quantification of the growth of cluster it is seen that as the size of the clusters increase there is preference for the coexistence of fcc/hcp orders at the expense of simple icosahedral ordering, although there is some contribution from distorted icosahedral ordering. It is found that even for aluminum clusters with 512 atoms distorted icosahedral ordering exists. For clusters with N≥256 atoms fcc ordering dominates, which implies that at this point we are already on the threshold of bulklike bonding

Prevalence of gastric mucosal interleukin-1 polymorphisms in Kenyan patients with advanced gastric cancer

Helicobacter pylori is the main cause of peptic ulceration, distal gastric adenocarcinoma, and gastric lymphoma.1 Worldwide, gastric cancer is the second most common malignancy in men and women.1 According to data from the Nairobi Cancer Registry, gastric cancer is the fourth most common malignancy in adult males and the fifth most common in adult females. However, this may not represent the true situation because of under-reporting of cases. In the development of gastric cancer, environmental factors such as smoking, diet and, in particular, infection with H. pylori are significant.1 Based on epidemiological studies, the International Agency for Research on Cancer (IARC) identified H. pylori as a ‘group 1 agent (definite carcinogen)’.2 H. pylori infection can result in decreased acid secretion with subsequent mucosal atrophy and intestinal metaplasia.1 Another precondition for mucosal atrophy is autoimmunity against parietal cells, which can mimic classic autoimmune gastritis with the presence of various autoantibodies in up to 40% of H. pylori-infected individuals.1 The occurrence of intestinal metaplasia, for which a relationship with gastric cancer is strongly suggested, has been demonstrated in approximately 60% of patients with H. pylori infection.1 The metaplasia may then progress to gastric cancer, especially to tumours of the intestinal type.1 Findings by Uemura et al. support the importance of these histological findings as a precancerous condition in H. pyloriassociated gastritis.3 However, only a minority of H. pyloriinfected patients develop gastric cancer, which underscores the notion that the host genetic background could be of critical importance. Data strongly suggest that the susceptibility to infection from H. pylori is mainly conferred by genes involved in inflammatory processes following colonisation with H. pylori.1 Chronic gastritis is characterised by the release of pro-inflammatory cytokines such as interleukin-1β (IL-1β) or tumour-necrosis factor alpha (TNFα), which are potent inhibitors of gastric acid secretion.1 Advanced-stage gastric cancer has been repeatedly associated with polymorphisms of the IL-1 gene cluster on chromosome 2q, which contains 3 related genes within a 430 kb region (IL-1A, IL-1B, and IL-1RN), encoding for IL-1α , IL-1β, and the endogenous receptor antagonist IL-1ra, respectively. It was hypothesised that genetic differences within these genes could influence the immune response against pathogens such as H. pylori and the development of premalignant histological alterations in the gastric mucosa.1 In patients with advanced-stage gastric cancer, an increased frequency of the IL-1B-31C and IL-1B-511T alleles and the uncommon IL-1B-31C/IL-1B-511T haplotype was demonstrated. In addition, the IL-1RN*2 allele and the homozygous genotype IL-1RN*2/2 were found in increased prevalence in gastric cancers.1 Subsequent studies confirmed these genetic associations.1 El-Omar et al. genotyped patients with gastric cancer according to tumour localisation (cardia v. non-cardia) and oesophageal cancers (adenocarcinomas v. squamous cell carcinomas) for various polymorphisms of genes encoding for pro- and anti-inflammatory cytokines.4 They described an increased risk for non-cardia gastric cancer in carriers of the IL-1B-511T allele, IL-1RN*2 homozygotes, carriers of the TNF-A-308A allele and the haplotype IL-10- 1082A/-819T/-592A. The cumulative risk depends on the number of high-risk alleles or genotypes per patient.4 A previous study confirmed the risk increase for development of gastric carcinoma in carriers of multiple proinflammatory genotypes.1 The alleles IL-1RN*2 and IL-1B-511T are associated with increased synthesis of the proinflammatory cytokine IL-1ß, and the allele TNFA-308A results in an increased production of the proinflammatory cytokine TNF.

Rooftop rainwater harvesting for Mombasa: Scenario development with image classification and water resources simulation

Mombasa faces severe water scarcity problems. The existing supply is unable to satisfy the demand. This article demonstrates the combination of satellite image analysis and modelling as tools for the development of an urban rainwater harvesting policy. For developing a sustainable remedy policy, rooftop rainwater harvesting (RRWH) strategies were implemented into the water supply and demand model WEAP (Water Evaluation and Planning System). Roof areas were detected using supervised image classification. Future population growth, improved living standards, and climate change predictions until 2035 were combined with four management strategies. Image classification techniques were able to detect roof areas with acceptable accuracy. The simulated annual yield of RRWH ranged from 2.3 to 23 million cubic meters (MCM) depending on the extent of the roof area. Apart from potential RRWH, additional sources of water are required for full demand coverage. © 2017 by the authors.DAA