811 research outputs found
Fragmentation of Lanthanide (III) Cationized Small Peptides: Generation of Peptide Radical Cations and Dipositive a and b ions.
This research work examines the dissociation chemistry of tripositive complexes formed by trivalent lanthanide ions and small peptides with tandem mass spectrometry under low-energy collision-induced dissociation (CID). By fragmentation of the tripositive lanthanide(III) cationized small peptide, a new route to generate peptide radical cations has been discovered. The dipositive b ions are also observed and the mechanisms by which they fragment are investigated by MSn.
Tripositive complexes of lanthanide(III)/peptide have similar fragmentation chemistries in the gas phase when lanthanide = yttrium, lanthanum, cerium, samarium, gadolinium and terbium; [a3+H]2+ ions are formed and there are no peptide radical cations observed. When the lanthanide is europium(III), radical cations of tryptophan-, tyrosine-, phenylalanine-, methionine-containing peptides and of aliphatic peptides have been generated.
Fragmentations of tripositive Ce(III)/peptide and Eu(III)/peptide complexes show very different behaviours. Abundant CO loss is only observed for dissociation of Ce(III)/peptide complexes, whereas CO2 loss is the predominant channel for Eu(III)/peptide complexes. Similarly, CO loss and CO2 loss are the predominant channels for the dissociations of [Ce(peptide-H)]2+ and [Eu(peptide-H)]2+, respectively. Peptide radical cations are only generated by the fragmentation of Eu(III)/peptide complexes, while protonated a and b ions are only observed when Ce(III)/peptide complexes dissociate.
The dissociations of aliphatic [peptide]+ions generate [b3-H]+/ [b2-H]+ions for most peptides. In the dissociation of [a3+H]+ions, [b2-H]+ions are formed from most peptides.
[a3+H]2+ ions usually cleave at the C-terminal amide bonds, creating two singly charged ions, a [b2]+ ion and an iminium ion derived from the C-terminal residue. Some [a3+H]2+ ions also lose small neutral molecules. The composition of the peptides dictates the preferred mode of the fragmentation of [b3+H]2+ ions, either loss of CO to form [a3+H]2+, or loss of CO plus H2O.
Fragmentations of [Ce(peptide-H)]2+ ions show CO loss, and CO2 losses are observed for peptides with aromatic side chains or a methionine residue at C-terminus. For [Ce(peptide-H)(peptide)]2+ complexes, neutral losses are also observed but formation of two singly charged ions is dominant. The dissociation behaviour of [Ce(peptide-H)(CH3CN)]2+ and [Eu(peptide-H)(CH3CN)]2+ complexes are quite different. The former loses only CH3CN whereas the latter loses only CO2
Adaptive Generalized Multiscale Model Reduction Techniques for Problems in Perforated Domains
Multiscale modeling of complex physical phenomena in many areas, including hydrogeology,
material science, chemistry and biology, consists of solving problems in highly
heterogeneous porous media. In many of these applications, differential equations are formulated
in perforated domains which can be considered as the region outside of inclusions
or connected bodies of various sizes. Due to complicated geometries of these inclusions,
solutions to these problems have multiscale features. Taking into account the uncertainties,
one needs to solve these problems extensively many times. Model reduction techniques
are significant for problems in perforated domains in order to improve the computational
efficiency.
There are some existing approaches for model reduction in perforated domains including
homogenization, heterogeneous multiscale methods and multiscale finite element
methods. These techniques typically consider the case when there is a scale separation or
the perforation distribution is periodic, and assume that the solution space can be approximated
by the solutions of directional cell problems and the effective equations contain a
limited number of effective parameters.
For more complicated problems where the effective properties may be richer, we are
interested in developing systematic local multiscale model reduction techniques to obtain
accurate macroscale representations of the underlying fine-scale problem in highly heterogeneous
perforated domains. In this dissertation, based on the framework of Generalized
Multiscale Finite Element Method, we develop novel methods and algorithms including
(1) development of systematic local model reduction techniques for computing multiscale
basis in perforated domains, (2) numerical analysis and exhaustive simulation utilizing the
proposed basis functions, (3) design of different applicable global coupling frameworks
and (4) applications to various problems with challenging engineering backgrounds. Our
proposed methods can significantly advance the computational efficiency and accuracy for
multiscale problems in perforated media
The LBFGS Quasi-Newtonian Method for Molecular Modeling Prion AGAAAAGA Amyloid Fibrils
Experimental X-ray crystallography, NMR (Nuclear Magnetic Resonance)
spectroscopy, dual polarization interferometry, etc are indeed very powerful
tools to determine the 3-Dimensional structure of a protein (including the
membrane protein); theoretical mathematical and physical computational
approaches can also allow us to obtain a description of the protein 3D
structure at a submicroscopic level for some unstable, noncrystalline and
insoluble proteins. X-ray crystallography finds the X-ray final structure of a
protein, which usually need refinements using theoretical protocols in order to
produce a better structure. This means theoretical methods are also important
in determinations of protein structures. Optimization is always needed in the
computer-aided drug design, structure-based drug design, molecular dynamics,
and quantum and molecular mechanics. This paper introduces some optimization
algorithms used in these research fields and presents a new theoretical
computational method - an improved LBFGS Quasi-Newtonian mathematical
optimization method - to produce 3D structures of Prion AGAAAAGA amyloid
fibrils (which are unstable, noncrystalline and insoluble), from the potential
energy minimization point of view. Because the NMR or X-ray structure of the
hydrophobic region AGAAAAGA of prion proteins has not yet been determined, the
model constructed by this paper can be used as a reference for experimental
studies on this region, and may be useful in furthering the goals of medicinal
chemistry in this field
China Business Perception Index
The Business Perception Index (BPI) has been developed to understand the Kenya-based Chinese companies' characteristics, to understand the business and investment climate faced by Chinese enterprises, and how these conditions affect productivity and growth of Chinese companies in Kenya. The BPI Survey-Kenya is a firm-level descriptive survey of Chinese private and state-owned enterprises in Kenya. The questionnaire includes the following ten major sections: basic firm characteristics, regulation and taxes, crime and safety, informality, gender, finance, infrastructure, trade, workforce, corruption and obstacles analysis. We reached out through email and telephone to 184 Chinese establishments in Kenya, and 75 companies accepted the survey
Deactivation of Soybean Agglutinin by Enzymatic and Other Physical Treatments
The main objective of this study was to eliminate the hemagglutination activity of an antinutritional factor in soybeans, soybean agglutinin (SBA). A series of experiments was designed to enzymatically modify SBA structure and to use other physical treatments to reduce activity. SBA extract was prepared from soy flour and used as the substrate for all treatments. Deglycosylation by enzyme decreased activity of SBA by 21%, but not to the level of denaturation by heat or by denaturing reagents (47−77% residual activity). Single enzymes, such as trypsin, chymotrypsin, thermolysin, and endoproteinase Glu-C, did not hydrolyze native SBA, but they hydrolyzed heat- or organic solute-denatured SBA. Even after hydrolysis, SBA still had 44−62% residual activity. Combinations of enzymes with thermolysin fully deactivated heat- or guanidine hydrochloride- and urea-treated SBA. Pepsin and pancreatin hydrolysis fully deactivated not only heated but also native SBA. Tea polyphenols, metal ions, and chelating agents were also tested, and they showed no significant effect on SBA activity. N-Acetylgalactosamine−agarose beads specifically but not fully removed SBA from the soy protein mixture. In general, SBA needs to be denatured first for an effective enzymatic hydrolysis, and multiple enzymes are needed to fully deactivate SBA. Pepsin and pancreatin treatment showed great promise in fully reducing SBA activity, and it would be further tested using soy flour as a model system
On a neural network approach for solving potential control problem of the semiclassical Schr\"odinger equation
Robust control design for quantum systems is a challenging and key task for
practical technology. In this work, we apply neural networks to learn the
control problem for the semiclassical Schr\"odinger equation, where the control
variable is the potential given by an external field that may contain
uncertainties. Inspired by a relevant work [29], we incorporate the
sampling-based learning process into the training of networks, while combining
with the fast time-splitting spectral method for the Schr\"odinger equation in
the semiclassical regime. The numerical results have shown the efficiency and
accuracy of our proposed deep learning approach
Job Performance Modeling: A Holistic Theoretical Analysis
The purpose of this study is to investigate inconsistent findings in extant research on organizational performance prediction. Systematic review is used to (a) evaluate the overall validity of traditional antecedents of organizational performance, (b) examine their underlying casual relationships in determining organizational performance, and (c) investigate the potential existence of mediating and moderating effects of each antecedent. Rather than simply making the customary plea for more elaborate micro theories of behavior or improved research designs, it is contended that greater progress could be made by examining and organizing what is already known about performance and its antecedents. Thus, leveraging on the systematic review analysis, this research develops a holistic theoretical model by blending three job performance antecedents to study their explanatory power and to reveal how these factors may interact with each other. The proposed causal-chain framework may be regarded as representative references for future research in the organizational psychology. Practitioners can also develop a better operational strategies based on the theoretical model
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