45 research outputs found
Direct and indirect excitation mechanisms in two-photon photoemission spectroscopy of Cu(111) and CO/Cu(111)
It is demonstrated that the dependence of the two-photon photoemission (2PPE) yield on the polarization of the exciting laser light provides detailed information about the excitation mechanism and the orientation of transition dipole moments in the 2PPE process. In particular, it is possible to distinguish between a direct two-photon excitation process, where both electronic transitions are induced by the electric fields at the surface, and an indirect mechanism, where the first excitation step occurs in the substrate. In the latter process the intermediate state in 2PPE is populated by scattering of photoexcited hot electrons from the substrate, which are subsequently photoemitted by the second laser pulse. The analysis is applied to 2PPE from clean and CO covered Cu(111). Furthermore, we have derived analytical expressions for the 2PPE signal based on the optical Bloch equations for a three-level system excited with continuous light beams. They allow us to calculate 2PPE spectra of surface states for a variety of cases
Dynamics of Electron-Induced Manipulation of Individual CO Molecules on Cu(111)
Electrons tunneling from a scanning tunneling microscope tip to individual CO molecules on Cu(111) can cause their hopping from the surface to the tip if the bias exceeds a threshold of 2.4 V. Polarization- and time-resolved two-photon photoemission identifies the underlying elementary process as intermediate population of a CO 2π* -derived level, which exhibits an ultrashort lifetime of 0.8–5 fs. From an isotope effect of 2.7 - 0.5 + 0.3 it can be calculated that ≈ 0.05 % of the tunneling current transiently occupies this level while a desorption of the excited molecule occurs only in 5 × 10 - 9 of the cases
Initial Quantitative Proteomic Map of 28 Mouse Tissues Using the SILAC Mouse
Identifying the building blocks of mammalian tissues is a precondition for understanding their function. In particular, global and quantitative analysis of the proteome of mammalian tissues would point to tissue-specific mechanisms and place the function of each protein in a whole-organism perspective. We performed proteomic analyses of 28 mouse tissues using high-resolution mass spectrometry and used a mix of mouse tissues labeled via stable isotope labeling with amino acids in cell culture as a "spike-in" internal standard for accurate protein quantification across these tissues. We identified a total of 7,349 proteins and quantified 6,974 of them. Bioinformatic data analysis showed that physiologically related tissues clustered together and that highly expressed proteins represented the characteristic tissue functions. Tissue specialization was reflected prominently in the proteomic profiles and is apparent already in their hundred most abundant proteins. The proportion of strictly tissue-specific proteins appeared to be small. However, even proteins with household functions, such as those in ribosomes and spliceosomes, can have dramatic expression differences among tissues. We describe a computational framework with which to correlate proteome profiles with physiological functions of the tissue. Our data will be useful to the broad scientific community as an initial atlas of protein expression of a mammalian species
Aniline incorporated silica nanobubbles
We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline
molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted
emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution,
precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of
gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective
removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The
material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and
voltammetric properties of the system were studied in order to understand the interaction of aniline with
the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the
silica shell
Bi-allelic loss-of-function variants in BCAS3 cause a syndromic neurodevelopmental disorder.
BCAS3 microtubule-associated cell migration factor (BCAS3) is a large, highly conserved cytoskeletal protein previously proposed to be critical in angiogenesis and implicated in human embryogenesis and tumorigenesis. Here, we established BCAS3 loss-of-function variants as causative for a neurodevelopmental disorder. We report 15 individuals from eight unrelated families with germline bi-allelic loss-of-function variants in BCAS3. All probands share a global developmental delay accompanied by pyramidal tract involvement, microcephaly, short stature, strabismus, dysmorphic facial features, and seizures. The human phenotype is less severe compared with the Bcas3 knockout mouse model and cannot be explained by angiogenic defects alone. Consistent with being loss-of-function alleles, we observed absence of BCAS3 in probands' primary fibroblasts. By comparing the transcriptomic and proteomic data based on probands' fibroblasts with those of the knockout mouse model, we identified similar dysregulated pathways resulting from over-representation analysis, while the dysregulation of some proposed key interactors could not be confirmed. Together with the results from a tissue-specific Drosophila loss-of-function model, we demonstrate a vital role for BCAS3 in neural tissue development
Observation of a direct transition in the sp-band of Cu(111) and (√3x√3)R30°-CO/Cu(111) in one- and two-photon photoemission
One- and two-photon photoemission (1PPE and 2PPE) spectroscopy has been employed to characterize electronic states of the Cu(111) and (3x3)R30°-CO/Cu(111) systems. A 2PPE process with an unusual wavelength dependence (ΔEkin=1.4Δhν) is observed and assigned to a direct transition from the lower to the upper branch of the copper sp-band. Good agreement (within ±25 to ±35 meV) between the experimental transitions and a two-band model for the Cu(111) band structure is obtained
Stable isotope and trace element stratigraphy across the Permian-Triassic transition: A redefinition of the boundary in the Velebit Mountain, Croatia
Stable isotopes of carbonates (delta(13)C(carb), delta(18)O(carb)),
organic matter (delta(13)C(org), delta(15)N(org)) and major, trace and
rare earth element (REE) compositions of marine carbonate rocks of Late
Permian to Early Triassic age were used to establish the position of the
Permian-Triassic boundary (PTB) at two continuous sections in the
Velebit Mountain, Croatia. The chosen sections - Rizvanusa and
Brezimenjaca - are composed of two lithostratigraphic units, the Upper
Permian Transitional Dolomite and the overlying Sandy Dolomite. The
contact between these units, characterized by the erosional features and
sudden occurrence of ooids and siliciclastic grains, was previously
considered as the chronostratigraphic PTB. The Sandy Dolomite is
characterized by high content of non-carbonate material (up to similar
to 30 wt.% insoluble residue), originated from erosion of the uplifted
hinterland. A relatively rich assemblage of Permian fossils (including
Geinitzina, Globivalvulina, Hemigordius, bioclasts of gastropods,
ostracods and brachiopods) was found for the first time in Sandy
Dolomite, 5 m above the lithologic boundary in the Rizvanusa section. A
rather abrupt negative delta(13)C(carb) excursion in both sections
appears in rocks showing no recognizable facies change within the Sandy
Dolomite, -2 parts per thousand at Rizvanusa and -1.2 parts per thousand
at Brezimenjaca, 11 m and 0.2 m above the lithologic contact,
respectively. This level within the lower part of the Sandy Dolomite is
proposed as the chemostratigraphic PTB. In the Rizvanusa section, the
delta(13)C(org) values decline gradually from similar to-25 parts per
thousand in the Upper Permian to similar to-29 parts per thousand in the
Lower Triassic. The first negative delta(13)C(org) excursion occurs
above the lithologic contact, within the uppermost Permian deposits, and
appears to be related to the input of terrigenous material. The release
of isotopically light microbial soil-biomass into the shallow-marine
water may explain this sudden decrease of delta(13)C(org) values below
the PTB. This would support the hypothesis that in the western Tethyan
realm the land extinction, triggering a sudden drop of woody vegetation
and related land erosion, preceded the marine extinction. The relatively
low delta(15)N(org) values at the Permian-Triassic (P-Tr) transition
level, close to approximate to 0 parts per thousand, and a secondary
negative delta(13)C(org) excursion of -0.5 parts per thousand point to
significant terrestrial input and primary contribution of cyanobacteria.
The profiles of the concentrations of redox-sensitive elements (Ce, Mn,
Fe, V), biogenic or biogenic-scavenged elements (P, Ba, Zn, V), Ce/Ce*
values, and normalized trace elements, including Ba/Al, Ba/Fe, Ti/Al,
Al/(Al + Fe + Mn) and Mn/Ti show clear excursions at the Transitional
Dolomite-Sandy Dolomite lithologic boundary and the chemostratigraphic
P-Tr boundary. The stratigraphic variations indicate a major regression
phase marking the lithologic boundary, transgressive phases in the
latest Permian and a gradual change into shallow/stagnant anoxic marine
environment towards the P-Tr boundary level and during the earliest
Triassic. (C) 2010 Elsevier B.V. All rights reserved