Search results for " Cluster"
showing 10 items of 2162 documents
The à 1Au state and the T2 potential surface of acetylene: Implications for triplet perturbations in the fluorescence spectra of the à state
1996
The cis–trans isomerization reaction on the T2 surface of acetylene and the lowest excited singlet state of acetylene, A 1Au, are investigated by ab initio electronic structure theory. We report optimized geometries, dipole moments, and harmonic vibrational frequencies of stationary points and adiabatic energy differences between them using basis sets as large as triple‐ζ plus double polarization with higher angular momentum functions, TZ(2df,2pd), and theoretical methods up to coupled‐cluster singles and doubles with a perturbative triples correction [CCSD(T)] and the equation‐of‐motion coupled‐cluster method (EOM‐CCSD). Our theoretical predictions should aid the interpretation of observat…
Water Structure Recovery in Chaotropic Anion Recognition: High-Affinity Binding of Dodecaborate Clusters to γ-Cyclodextrin
2015
Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25 kcal mol(-1)) and entropies (TΔS up to -18.4 kcal mol(-1), both for B12I12(2-)), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous …
Micro magnetofluidics: droplet manipulation of double emulsions based on paramagnetic ionic liquids
2013
The ability to control and manipulate discrete fluid droplets by magnetic fields offers new opportunities in microfluidics. A surfactant-free and easy to realize technique for the continuous generation of double emulsion droplets, composed of an organic solvent and a paramagnetic ionic liquid, is applied. The inner phase of the emulsion droplet consists of imidazolium-based ionic liquids with either iron, manganese, nickel or dysprosium containing anions which provide paramagnetic behaviour. The double emulsion droplets are dispersed in a continuous phase of FC-40. All substances - the organic phase, the paramagnetic ionic liquid and the continuous phase -are immiscible. The magnetic proper…
Computed positron lifetimes in vacancies and vacancy-iron clusters in gold
1983
Abstract Annihilation characteristics are calculated for positrons trapped in clean and impurity decorated vacancy clusters in Au. The positron lifetime depends strongly on the structure of the clusters. In a strongly relaxed vacancy cluster, the lifetime can become smaller than the lifetime in a single vacancy. The substitution of some neighbour atoms of a vacancy cluster by Fe atoms has only a minor effect on the positron lifetimes.
Mitigating DDoS using weight‐based geographical clustering
2020
Distributed denial of service (DDoS) attacks have for the last two decades been among the greatest threats facing the internet infrastructure. Mitigating DDoS attacks is a particularly challenging task as an attacker tries to conceal a huge amount of traffic inside a legitimate traffic flow. This article proposes to use data mining approaches to find unique hidden data structures which are able to characterize the normal traffic flow. This will serve as a mean for filtering illegitimate traffic under DDoS attacks. In this endeavor, we devise three algorithms built on previously uncharted areas within mitigation techniques where clustering techniques are used to create geographical clusters …
Fragmentation of anthracene C14H10, acridine C13H9N and phenazine C12H8N2 ions in collisions with atoms
2014
International audience; We report experimental total, absolute, fragmentation cross sections for anthracene C14H10, acridine C13H9N, and phenazine C12H8N2 ions colliding with He at center-of-mass energies close to 100 eV. In addition, we report results for the same ions colliding with Ne, Ar, and Xe at higher energies. The total fragmentation cross sections for these three ions are the same within error bars for a given target. The measured fragment mass distributions reveal significant contributions from both delayed (≫10−12 s) statistical fragmentation processes as well as non-statistical, prompt (∼10−15 s), single atom knockout processes. The latter dominate and are often followed by sec…
Alternative Biosynthetic Starter Units Enhance the Structural Diversity of Cyanobacterial Lipopeptides
2019
Puwainaphycins (PUWs) and minutissamides (MINs) are structurally analogous cyclic lipopeptides possessing cytotoxic activity. Both types of compound exhibit high structural variability, particularly in the fatty acid (FA) moiety. Although a biosynthetic gene cluster responsible for synthesis of several PUW variants has been proposed in a cyanobacterial strain, the genetic background for MINs remains unexplored. Herein, we report PUW/MIN biosynthetic gene clusters and structural variants from six cyanobacterial strains. Comparison of biosynthetic gene clusters indicates a common origin of the PUW/MIN hybrid nonribosomal peptide synthetase and polyketide synthase. Surprisingly, the biosynthet…
Diversity and Evolution of the Phenazine Biosynthesis Pathway
2010
ABSTRACT Phenazines are versatile secondary metabolites of bacterial origin that function in biological control of plant pathogens and contribute to the ecological fitness and pathogenicity of the producing strains. In this study, we employed a collection of 94 strains having various geographic, environmental, and clinical origins to study the distribution and evolution of phenazine genes in members of the genera Pseudomonas , Burkholderia , Pectobacterium , Brevibacterium , and Streptomyces . Our results confirmed the diversity of phenazine producers and revealed that most of them appear to be soil-dwelling and/or plant-associated species. Genome analyses and comparisons of phylogenies inf…
GNPS-guided discovery of xylacremolide C and D, evaluation of their putative biosynthetic origin and bioactivity studies of xylacremolide A and B
2021
Targeted HRMS2-GNPS-based metabolomic analysis of Pseudoxylaria sp. X187, a fungal antagonist of the fungus-growing termite symbiosis, resulted in the identification of two lipopeptidic congeners of xylacremolides, named xylacremolide C and D, which are built from d-phenylalanine, l-proline and an acetyl-CoA starter unit elongated by four malonyl-CoA derived ketide units. The putative xya gene cluster was identified from a draft genome generated by Illumina and PacBio sequencing and RNAseq studies. Biological activities of xylacremolide A and B were evaluated and revealed weak histone deacetylase inhibitory (HDACi) and antifungal activities, as well as moderate protease inhibition activity …
A Hardware and Secure Pseudorandom Generator for Constrained Devices
2018
Hardware security for an Internet of Things or cyber physical system drives the need for ubiquitous cryptography to different sensing infrastructures in these fields. In particular, generating strong cryptographic keys on such resource-constrained device depends on a lightweight and cryptographically secure random number generator. In this research work, we have introduced a new hardware chaos-based pseudorandom number generator, which is mainly based on the deletion of an Hamilton cycle within the $N$ -cube (or on the vectorial negation), plus one single permutation. We have rigorously proven the chaotic behavior and cryptographically secure property of the whole proposal: the mid-term eff…