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91.
In this paper, the problem of internal finite‐time stabilization for 1‐D coupled wave equations with interior point mass is handled. The nonlinear stabilizing feedback law leads, in closed‐loop, to nonlinear evolution equations where Kato theory is used to prove the well‐posedness. In addition, it is showed that in some cases, the solution of this hybrid system is constant in finite‐time if we use Neumann boundary conditions. This result can be improved (in complete finite‐time stability sense) if we change the above feedback. 相似文献
92.
This paper describes mechanistic studies aimed at understanding the origin of two important side events accompanying the linear polycondensation of furfuryl alcohol in acidic media. The first process concerns the formation of conjugated sequences along the polymeric chains. The use of model monomers and compounds simulating the structure of the linear polymer provided for the first time a full understanding of the reactions leading to multiple unsaturations. The main culprits for this process are the labile hydrogen atoms on the methylene moiteties bridging the furan rings. The second anomaly in these systems concerns the formation of networks following a complex branching mechanism. Again, model structures helped to pinpoint the origin of this process and to propose plausible reactions to describe it. 相似文献
93.
Kleinova M Belgacem O Pock K Rizzi A Buchacher A Allmaier G 《Rapid communications in mass spectrometry : RCM》2005,19(20):2965-2973
Three samples of albumin derived from human plasma (pharmaceutical grade, HSA) obtained from different commercial sources were investigated for their micro-heterogeneities by means of electrospray ionization (ESI) ion trap mass spectrometry (ITMS). The study covered MS analyses of the intact proteins as well as on the tryptic peptide level. The intact protein samples were analyzed without any separation step except for simple desalting. With these samples we observed in the positive ion ESI mass spectra that the multiply charged ion signals of HSA consisted of a number of fully or partly resolved peaks with relative intensities depending on the analyzed sample. The non-modified form of HSA was detected in the three HSA preparations at m/z values of 66448 +/- 3.6, 66450 +/- 0.6 and 66451 +/- 3.2 ([MH]+), respectively. The value calculated from the amino acid sequence was 66439. The second compound present with high intensity (in two cases the base peak in the deconvoluted mass spectrum) is interpreted as a modified HSA, and the molecular mass increase in relation to the unmodified HAS was between 116 and 118 Da (m/z of 66 564, 66 567 and 66 569), suggesting the presence of a covalently bound cysteine residue. A further peak in the deconvoluted ESI spectra was found in all three samples with rather low signal/noise ratio at m/z 66 619, 66 621 and 66 613, respectively, which may correspond to a non-enzymatic glycation described in the literature. The verification of the proposed covalent HSA modifications was subsequently done on the peptide level using high-performance liquid chromatography (HPLC)/ESI-MS and HPLC/ESI-MS/MS including low-energy collision-induced dissociation (CID). Prior to the tryptic digestion, the HSA samples were alkylated without a prior reduction step. Following this procedure we detected peptides of the sequence T21-41 that included the Cys-34 residue in both forms: cysteinylated (m/z 639.15 [M+4H]4+) as well as vinylpyridine-alkylated (m/z 635.69 [M+4H]4+, which means in its previously native free SH form). In the next step on-line LC/ESI low-energy CID MS/MS experiments were performed to verify these two proposed structures. By means of MS/MS analysis of the mentioned ions the described modification (cysteinylation) at the Cys-34 residue could be proven. This abundant modification of HSA in pharmaceutical-grade preparations could be unambiguously identified as cysteinylation at the Cys-34 residue. On the other hand, the proposed non-enzymatic glycation was not detectable on the peptide level in the on-line HPLC/ESI-MS mode, maybe due to the low concentration in the three samples under investigation. 相似文献
94.
We performed an ab initio study using a method named linearized augmented plane wave with a full potential (FP-LAPW) based on the density functional theory. We predicted the physical properties of Ru2VGexSb1−x (x = 0, 0.5 and 1) Heusler alloys in L21 structure. We computed the magnetic and structural properties using the general gradient approximation. The modified Becke-Johnson scheme was used to study the electronic structure of these compounds. The obtained results show that the lattice constants and the spin magnetic moments are in favorable agreement compared with theoretical values and experimental data. The computed densities of state (DOSs) of these compounds indicate a half-metallic behavior with a real gap for the ternary materials, which gives perfect spin polarization, while for the quaternary one, the DOS indicate a nearly half-metallic character with a pseudogap in the minority spin close to the Fermi level EF. 相似文献
95.
A. Mansri B. Bouras L. Tennouga G. Clisson B. Grassl 《Research on Chemical Intermediates》2014,40(1):269-279
The interactions of oppositely charged polyelectrolyte and surfactant (anionic polyacrylamide AD37 and dodecylpyridinium chloride DPC, respectively) in aqueous solution were studied at 25 °C by measurement of viscosity and conductivity. The system was investigated in aqueous medium in the absence and presence of NaCl. The AD37 interacts strongly with the DPC surfactant of the opposite charge. The interactions are electrostatic and hydrophobic. Thus, they are manifested in the formation of hydrophobic aggregates. The critical aggregation concentration (CAC) is much lower than the critical micellar concentration (CMC) of the surfactant alone. However, the value of the saturation concentration X 2 is higher. The ionic strength of the medium after addition of salt explains an important part of these interactions. In fact, the electrolyte charge affects the CMC and the CAC values. 相似文献
96.
Abir Razzak Ramzi Khiari Younes Moussaoui Mohamed Naceur Belgacem 《Molecules (Basel, Switzerland)》2022,27(19)
Schinus molle (SM) was investigated as a primary source of cellulose with the aim of discovering resources to generate cellulose nanofibers (CNF). The SM was put through a soda pulping process to purify the cellulose, and then, the fiber was treated with an enzymatic treatment. Then, a twin-screw extruder and/or masuko were utilized to help with fiber delamination during the nanofibrillation process. After the enzymatic treatment, the twin-screw extruder and masuko treatment give a yield of 49.6 and 50.2%, respectively. The optical and atomic force microscopy, morfi, and polymerization degrees of prepared cellulosic materials were established. The pulp fibers, collected following each treatment stage, demonstrated that fiber characteristics such as length and crystallinity varied according to the used treatment (mechanical or enzymatic treatment). Obviously, the enzymic treatment resulted in shorter fibers and an increased degree of polymerization. However, the CNF obtained after enzymatic and extrusion treatment was achieved, and it gave 19 nm as the arithmetic width and a Young’s modulus of 8.63 GPa. 相似文献
97.
Belgacem O Buchacher A Pock K Josic D Sutton C Rizzi A Allmaier G 《Journal of mass spectrometry : JMS》2002,37(11):1118-1130
Human plasma-derived antithrombin III (AT-III), factor IX (FIX) and vitronectin (VN) were characterized as native glycoproteins and in their de-N-glycosylated form by means of MALDI mass spectrometry. The average molecular masses of the three complex glycoproteins were determined applying internal calibration with high-mass, well-defined protein calibrants. Internal calibration generated for the 47 kDa yeast protein enolase a mass precision in the continuous and delayed extraction mode of +/-0.12 and +/-0.022%, respectively. The achievable mass accuracy for such a high-mass, unmodified protein was in the range of 0.02% in the continuous mode, which turned out to be better than in the delayed extraction mode. Purification of all (glyco) proteins (even the calibration proteins) by means of ZipTip technology and direct elution with a solvent system containing the appropriate MALDI matrix turned out to be a prerequisite to measure the exact molecular masses with an internal calibration. The average molecular masses of the two different forms of AT-III, namely AT-III(alpha) and AT-III(beta), were shown to be 57.26 and 55.04 kDa, respectively. The 2.22 kDa mass difference is attributed to the known difference in carbohydrate content at one specific site (Asn-135). After exhaustive de-N-glycosylation (by means of PNGase F) of the alpha- and beta-form and subsequent MALDI-MS analysis, average molecular masses of 48.96 and 48.97 kDa, respectively, were obtained. These values are in good agreement (-0.15%) with the calculated molecular mass (49.039 kDa) of the protein part based on SwissProt data. The molecular mass of the heavily post-translational modified glycoprotein FIX was found to be 53.75 kDa with a peak width at 10% peak height of 4.5 kDa, because of the presence of many different posttranslational modifications (N- and O-glycosylation at multiple sites, sulfation, phosphorylation, hydroxylation and numerous gamma-carboxyglutamic acids). MALDI-MS molecular mass determination of the native, size-exclusion chromatography-purified, VN sample revealed that the glycoprotein was present as dimer with molecular mass of 117.74 kDa, which could be corroborated by non-reducing SDS-PAGE. After sample treatment with guanidine hydrochloride and mass spectrometric analysis, a single, new main component was detected. The molecular mass turned out to be 59.45 kDa, representing the monomeric form of VN, known as V75. The determined molecular mass value was shown to be on one hand lower than from SDS-PAGE and on the other higher than the calculated amino acid sequence molecular mass (52 277 Da), pointing to the well-known SDS-PAGE bias and to considerable post-translational modifications. Further treatment of the sample with a reducing agent and subsequent MALDI-MS revealed two new components with molecular masses of 49.85 and 9.41 kDa, corresponding to V65 and V10 subunits of VN. PNGase F digest of the V75 and V65 units and MS analysis, exhibiting a molecular mass reduction of 6.37 kDa in both cases, verified the presence of a considerable amount of N-glycans. 相似文献
98.
Belgacem O Bowdler A Brookhouse I Brancia FL Raptakis E 《Rapid communications in mass spectrometry : RCM》2006,20(11):1653-1660
A commercial matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) instrument equipped with a curved field reflectron (CFR) was modified in order to perform collision-induced dissociation (CID) on a variety of biomolecules. The incorporation of a high-resolution ion gate together with a collision cell within the field-free region allowed tandem mass analysis (MS/MS), without the necessity to decelerate the precursor ions prior to activation. The simultaneous detection of all product ions remained possible by using the CFR. To test the MS/MS performances, ACTH (fragment 1-17), a complex high mannose carbohydrate (Man)(8)(GlcNac)(2) and a lysophosphatidylcholine lipid (18:1) were analysed on the modified instrument. Direct comparison with the low-energy product ion spectra, acquired on a MALDI quadrupole ion trap (QIT) two-stage reflectron time-of flight (ReToF) mass spectrometer, showed significant differences in the types of product ions observed. The additional ions detected were a clear indication of the high-energy fragmentation processes occurring in the collision cell. 相似文献
99.
100.
Gerald Stübiger Ernst Pittenauer Omar Belgacem Pavel Rehulka Kurt Widhalm Günter Allmaier 《Rapid communications in mass spectrometry : RCM》2009,23(17):2711-2723
An improved analytical strategy for the analysis of complex lipid mixtures using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) in combination with high‐performance thin‐layer chromatography (HPTLC) is reported. Positive ion MALDI RTOF MS was applied as a rapid screening tool for the various neutral (e.g. triacylglycerols) and polar (e.g. glycerophospholipids and ‐sphingolipids) lipid classes derived from crude lipid extracts of e.g. human plasma as well as soybean lecithin. Finally, MALDI seamless post‐source decay (PSD) product ion analysis was performed in order to obtain further structural information (head‐ and acyl‐group identification) of selected lipid species and structure verification. A Coomassie Brilliant Blue R‐250 staining protocol for lipids on HPTLC plates was evaluated and was found to be fully compatible with subsequent MALDI‐MS. Lipids were analyzed after elution from the HPTLC phase material of the selected band (corresponding to certain lipid classes) by using the proper organic solvent mixture or in few cases directly from the HPTLC plates (a type of on‐line HPTLC/MALDI‐MS coupling). More than 70 distinct lipid species from seven different lipid classes in the range between m/z 500 and 1500 could be identified from the lipid extracts of human plasma and soybean lecithin, respectively. The general high sensitivity of MALDI‐MS detection allowed the analysis of even minor lipid classes from only very small volumes of human plasma (50 µL). The combination of HPTLC, Coomassie staining and positive ion MALDI curved field RTOF‐MS represents a straightforward strategy during lipidomics studies of food and clinically relevant human lipid samples. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献