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51.
John D. Barrow 《Physics letters. [Part B]》1981,107(5):358-360
We recalculate the cosmological limits on hypothetical and undetected elementary particle masses under the assumption that the cosmological constant, Λ, is non-zero. The existing range of allowed masses is considerably extended by removing the unverified assumption that Λ=0. In particular, light neutrino masses up to ≈280 eV are compatible with cosmological observations. The implications of a cold early universe for these estimates are also outlined. 相似文献
52.
This note is concerned with the origin of secondary flow in straight noncircular ducts. A critical examination of the analytical expressions for the secondary flow production terms is made to show that the essential requirement for secondary flow is a finite gradient of the difference in the turbulent stresses in the plane of the duct cross section in a peripheral direction. This conclusion has been reached following an investigation of the turbulent stress distributions in unidirectional pipe flow and assumes that, in general, the normal stresses only are significant in secondary flow production. An observation is made on “vorticity reversal” in the immediate vicinity of the boundary of a noncircular duct. 相似文献
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Ujjal Debnath Subenoy Chakraborty John D. Barrow 《General Relativity and Gravitation》2004,36(2):231-243
We study the occurrence and nature of naked singularities for a dust model with non-zero cosmological constant in (n+2)-dimensional Szekeres space-times (which possess no Killing vectors) for n 2. We find that central shell-focusing singularities may be locally naked in higher dimensions but depend sensitively on the choice of initial data. In fact, the nature of the initial density determines the possibility of naked singularity in space-times with more than five dimensions. The results are similar to the collapse in spherically symmetric Tolman-Bondi-Lemaître space-times. 相似文献
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56.
Huilin Li Jonathon R. Snelling Mark P. Barrow James H. Scrivens Peter J. Sadler Peter B. O’Connor 《Journal of the American Society for Mass Spectrometry》2014,25(7):1217-1227
To further explore the binding chemistry of cisplatin (cis-Pt(NH3)2Cl2) to peptides and also establish mass spectrometry (MS) strategies to quickly assign the platinum-binding sites, a series of peptides with potential cisplatin binding sites (Met(S), His(N), Cys(S), disulfide, carboxyl groups of Asp and Glu, and amine groups of Arg and Lys, were reacted with cisplatin, then analyzed by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Radical-mediated side-chain losses from the charge-reduced Pt-binding species (such as CH3S? or CH3SH from Met, SH? from Cys, CO2 from Glu or Asp, and NH2 ? from amine groups) were found to be characteristic indicators for rapid and unambiguous localization of the Pt-binding sites to certain amino acid residues. The method was then successfully applied to interpret the top-down ECD spectrum of an inter-chain Pt-crosslinked insulin dimer, insulin?+?Pt(NH3)2?+?insulin (>10 kDa). In addition, ion mobility MS shows that Pt binds to multiple sites in Substance P, generating multiple conformers, which can be partially localized by collisionally activated dissociation (CAD). Platinum(II) (Pt(II)) was found to coordinate to amine groups of Arg and Lys, but not to disulfide bonds under the conditions used. The coordination of Pt to Arg or Lys appears to arise from the migration of Pt(II) from Met(S) as shown by monitoring the reaction products at different pH values by ECD. No direct binding of cisplatin to amine groups was observed at pH 3?~?10 unless Met residues were present in the sequence, but noncovalent interactions between cisplatin hydrolysis and amination [Pt(NH3)4]2+ products and these peptides were found regardless of pH. Figure
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57.
Andrea F. Lopez-Clavijo Carlos A. Duque-Daza Andrew Soulby Isolda Romero Canelon Mark Barrow Peter B. O’Connor 《Journal of the American Society for Mass Spectrometry》2014,25(12):2125-2133
Glyoxal-derived advanced glycation end-products (AGEs) are formed in physiological systems affecting protein/peptide function and structure. These AGEs are generated during aging and chronic diseases such as diabetes and are considered arginine glycating agents. Thus, the study of glyoxal-derived AGEs in lysine residues and amino acid competition is addressed here using acetylated and non-acetylated undecapeptides, with one arginine and one lysine residue available for glycation. Tandem mass spectrometry results from a Fourier transform ion cyclotron resonance mass spectrometer showed glycated species at both the arginine and lysine residues. One species with the mass addition of 116.01096 Da is formed at the arginine residue. A possible structure is proposed to explain this finding (Nδ-[2-(dihydroxymethyl)-2H,3aH,4H,6aH-[1, 3]dioxolo[5,6-d]imidazolin-5-yl]-L-ornithine-derived AGE). The second species corresponded to intramolecular crosslink involving the lysine residue and its presence is checked with ion-mobility mass spectrometry. Graphical Abstract
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58.
Ziqing Weng Hongbin Wang Jitraporn Vongsvivut Runqing Li Alexey M. Glushenkov Jin He Ying Chen Colin J. Barrow Wenrong Yang 《Analytica chimica acta》2013
Molecule-coated nanoparticles are hybrid materials which can be engineered with novel properties. The molecular coating of metal nanoparticles can provide chemical functionality, enabling assembly of the nanoparticles that are important for applications, such as biosensing devices. Herein, we report a new self-assembly of core-satellite gold nanoparticles linked by a simple amino acid l-Cysteine for biosensing of Cu2+. The plasmonic properties of core-satellite nano-assemblies were investigated, a new red shifted absorbance peak from about 600 to 800 nm was found, with specific wavelength depending on ratios with assembly of large and small gold nanoparticles. The spectral features obtained using surface-enhanced Raman spectroscopy (SERS) provided strong evidence for the assembly of the Cu2+ ions to the L-Cysteine molecules leading to the successful formation of the core-satellite Cu(l-Cysteine) complex on the gold surfaces. In addition, a linear relationship between the concentration of mediating Cu2+ and absorbance of self-assembled gold nanoparticles (GNPs) at 680 nm was obtained. These results strongly address the potential strategy for applying the functionalized GNPs as novel biosensing tools in trace detections of certain metal ions. 相似文献
59.
Despite its central role in modern cosmology, doubts are often expressed as to whether cosmological inflation is really a falsifiable theory. We distinguish two facets of inflation, one as a theory of initial conditions for the hot big bang and the other as a model for the origin of structure in the Universe. We argue that the latter can readily be excluded by observations, and that there are also a number of ways in which the former can find itself in conflict with observational data. Both aspects of the theory are indeed falsifiable. 相似文献
60.