The formation of multiply charged molecular ions via the field-assisted ion evaporation mechanism during electrospray ionization enables the use of an atmospheric pressure ionization quadrupole mass spectrometer system for characterizing biologically important peptides. The straightforward implementation of high-performance liquid chromatography (HPLC) into this new strategy to determine the molecular weight of tryptic peptides via the pneumatically assisted electrospray (ion spray) interface is presented. Examples utilizing both microbore (1.0 mm) and standard bore (4.6 mm) inside diameter columns are shown for the LC/MS molecular weight determination of tryptic peptides in methionyl-human growth hormone (met-hGH). Injected levels from 50 to 75 pmol of tryptic digest onto 1 mm i.d. HPLC columns provided full-scan LC/MS or LC/MS/MS results without postcolumn splitting of the effluent. When standard 4.6 mm i.d. HPLC columns were used, a 20:1 postcolumn split was utilized, which required from 1 to 5 nmol of injected tryptic digest for full-scan LC/MS or LC/MS/MS results. Collision-induced dissociation (CID) mass spectra resulting from either "infusion" or on-line LC/MS/MS analysis of the abundant doubly charged ions that predominate for tryptic peptides under electrospray conditions provided structurally useful sequence information for met-hGH and human hemoglobin tryptic digests. The slower mass spectrometer scan rate used during infusion of sample provides more accurate mass assignments than on-line LC/MS or LC/MS/MS, but the latter on-line experiments preclude ambiguities caused by matrix or component interferences. However, in some instances very weak CID product ions preclude complete tryptic peptide structural characterization based upon the CID data alone.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
A study has been made of the influence of initial surface roughness, renewable and non-renewable surface contaminants, and irradiation hardening on the coefficient of friction for one LiF single crystal (A) sliding on another (B) in {100}A<010>A{100}B 010B orientation at 295 K. The normal load was 1 N, the nominal contact pressure 0.1 MPa, the sliding velocity 0.2 to 0.6 mm sec–1, and the amplitude of the (reciprocate) motion a few millimetres. Any influence of non-renewable contaminants persisted only for cumulative relative displacements 0.1 m, and that of micrometre-scale initial surface roughness only for a few metres. At steady state in the presence of renewable contaminants the coefficient of friction varied only from a high of 0.45 in ultra-high vacuum ( 7.5 × 10–8 Pa) and dry nitrogen-rich air ( 105 Pa, relative humidity 15%) to a low of 0.38 in moist nitrogen-rich air ( 105 Pa, relative humidity 50%). Irradiation hardening had no effect on the coefficient of friction at steady state. The worn surfaces created by steady-state sliding always exhibited a grooved topography partly obscured by more-or-less adherent layers of variously consolidated equiaxed debris particles 100 nm in size. Owing to the action of image forces, these particles contained no dislocations. It is suggested that the coefficient of friction was determined at steady state by the stress needed to shear these tiny particles past one another as near-rigid bodies. 相似文献
Person re-identification plays important roles in many practical applications. Due to various human poses, complex backgrounds and similarity of person clothes, person re-identification is still a challenging task. In this paper, we mainly focus on the robust and discriminative appearance feature representation and proposed a novel multi-appearance method for person re-identification. First, we proposed a deep feature fusion method and get the multi-appearance feature by combining two Convolutional Neural Networks. Then, in order to further enhance the representation of the appearance feature, the multi-part model was constructed by combining the whole body and the six body parts. Additionally, we optimized the feature extraction process by adding a pooling layer. Comprehensive and comparative experiments with the state-of-the-art methods over publicly available datasets demonstrated that the proposed method can get promising results.
Multimedia Tools and Applications - The pedestrian re-identification problem (i.e., re-id) is essential and pre-requisite in multi-camera video surveillance studies, provided the fact that... 相似文献