Proliferation of individual cells is one of the hallmarks of living systems, and collectively the cells within a colony or tissue form highly structured patterns, influencing the properties at the ...population level. We investigate the joint effect of proliferation in the form of cell division and cell sorting due to differential adhesion using a cellular automaton model. Through simulations and theoretical analysis akin to interface growth, we show that this model gives rise to slower than exponential growth in the case of a single cell type as well as novel colony patterns in the case of two cell types. In particular, engulfment of one cell type by the other is strongly enhanced compared to the prediction from the differential adhesion hypothesis in the absence of proliferation. These observations provide new insights in predicting and characterizing colony morphology using experimentally accessible information such as single cell growth rate and cell adhesion strength.
Single, double, and triple ionization of C(1+) ions by single photons is investigated in the energy range of 286-326 eV, i.e., in the range from the lowest-energy K-vacancy resonances to well beyond ...the K-shell ionization threshold. Clear signatures of C(1+)(1s2s(2)2p(2) (2)D,(2)P) resonances are found in the triple-ionization channel. The only possible mechanism producing C(4+)(1s(2)) via these resonances is direct triple-Auger decay, i.e., a four-electron process with simultaneous emission of three electrons.
The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for ...which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H
two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.
We present studies on intra-molecular charge redistribution in iodine containing molecules upon iodine-4d photoionization. For this, we employed an XUV-pump-XUV-probe scheme based on time-delayed ...femtosecond pulses delivered by the free-electron laser at DESY in Hamburg (FLASH). The experimental results show delay dependent and molecule-specific iodine charge state distributions that arise upon multiple iodine-4d photoionization. Using the example of CH3I and CH2I2, we compare the delay-dependent yields of I3+. We model the involved processes using advanced ab initio electronic structure calculations which include electron correlations combined with a classical model of the nuclear motion. The qualitative agreement of our model with the experimental results allows us to relate the observed, strongly molecule-specific efficiencies of the intra-molecular charge rearrangement not only to molecule-specific fragmentation timescales but also to molecule-specific electronic structure and molecular environment.
The F 1s core level photoionization of the ionic molecular radical HF+ has been studied using the photon–ion merged-beams technique at a synchrotron radiation source. Upon analyzing kinetic energy ...release (KER) dependent photoion yield spectra, complex ultrafast dissociation dynamics of the F 1s core hole excited σ* state can be revealed. By means of configuration–interaction electronic structure calculations of the excited molecular potential energy curves, this complex process can be attributed to a spin-dependent dissociation of the excited σ* biradical state.
We report on a kinematically complete measurement of double ionization of helium by a single 1100 eV circularly polarized photon. By exploiting dipole selection rules in the two-electron continuum ...state, we observed the angular emission pattern of electrons originating from a pure quadrupole transition. Our fully differential experimental data and companion ab initio nonperturbative theory show the separation of dipole and quadrupole contributions to photo-double-ionization and provide new insight into the nature of the quasifree mechanism.
The multiple ionisation of atomic Mn, excited at (photon energy: 52.1 eV) and above (photon energy: 61.1 eV) the discrete giant 3 p - 3 d resonance, was studied using high irradiation ...free-electron-laser soft x-ray pulses from the BL2 beamline of FLASH, DESY, Hamburg. In particular, the impact of the giant resonance on the ionisation mechanism was investigated. Ion mass-over-charge spectra were obtained by means of ion time-of-flight spectrometry. For the two photon energies, the yield of the different ionic charge states Mn q + (q = 0-7) was determined as a function of the irradiance of the soft x-ray pulses. The maximum charge state observed was Mn6+ for resonant excitation at 52.1 eV and Mn7+ for non-resonant excitation at 61.1 eV at a maximum irradiation of 3 × 10 13 W cm − 2 .
Prevention of neuronal apoptosis has been introduced as a new therapeutic strategy for neurodegenerative disorders. We have previously reported anti-apoptotic effects of transforming growth factor-β1 ...(TGF-β1), a multifunctional cytokine, in models of cerebral ischemia and in cultured neurons and recently focused on the mechanisms underlying the anti-apoptotic effect of TGF-β1. The anti-apoptotic transcriptional factor nuclear factor kappa B (NF-κB) shows high impact in the cell survival function of multiple cytokines and growth factors. The present study explored whether NF-κβ is a target of TGF-β1 and which signaling pathways involved in the activation of NF-κβ are triggered by TGF-β1. We demonstrated that TGF-β1 increased the transcriptional activity of NF-κβ in cultured hippocampal neurons in a time- and concentration-dependent manner. Furthermore, TGF-β1 induced translocation of p65/NF-κβ to the nucleus and enhanced NF-κβ transcriptional activity in the presence of apoptotic stimuli. TGF-β1-mediated NF-κβ activation was blocked by wortmannin and U0126, indicating the involvement of both phosphatidylinositol-3-OH kinase (PI3k)/Akt and mitogen-activated protein kinase (MAPK)/extracellular-signal regulated kinase (Erk)1,2 pathways in the action of TGF-β1. TGF-β1 produced a concomitant increase in the phosphorylations of Iκβ kinase (IKKα/β) and Iκβα with a subsequent degradation of Iκβα. Interestingly, the increased phosphorylation of IKKα/β and Iκβα was abrogated by wortmannin, but not by U0126, suggesting that PI3k/Akt and MAPK/Erk1,2 pathways triggered by TGF-β1 regulated the activation of NF-κβ through different mechanisms. Of note, wortmannin and U0126, as well as κβ-decoy DNA, abolished the anti-apoptotic effect of TGF-β1, corroborating the notion that both PI3k/Akt and MAPK/Erk1,2 pathways, and NF-κβ activity are necessary for the anti-apoptotic activity of TGF-β1.
Being a dual purpose enzyme, the DNA polymerase is responsible for elongation of the newly formed DNA strand as well as cleaving the erroneous growth in case of a misincorporation. The efficiency of ...replication depends on the coordination of the polymerization and exonuclease activity of DNA polymerase. Here, we propose and analyze a minimal kinetic model of DNA replication and determine exact expressions for the velocity of elongation and the accuracy of replication. We first analyze the case without exonuclease activity. In that case, accuracy is determined by a kinetic competition between stepping and unbinding, with discrimination between correct and incorrect nucleotides in both transitions. We then include exonuclease activity and ask how different modes of additional discrimination in the exonuclease pathway can improve the accuracy while limiting the detrimental effect of exonuclease on the speed of replication. In this way, we ask how the kinetic parameters of the model have to be set to coordinate the two activities of the enzyme for high accuracy and high speed. The analysis also shows that the design of a replication system does not universally have to follow the speed-accuracy trade-off rule, although it does in the biologically realized parameter range. The accuracy of the process is mainly controlled by the crucial role of stepping after erroneous incorporation, which has impact on both polymerase and exonuclease activities of DNA polymerase.
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