On the Role of Physics in the Growth and Pattern Formation of Multi-Cellular Systems: What can we Learn from Individual-Cell Based Models?

We demonstrate that many collective phenomena in multi-cellular systems can be explained by models in which cells, despite their complexity, are represented as simple particles which are parameterized mainly by their physical properties. We mainly focus on two examples that nevertheless span a wide range of biological sub-disciplines: Unstructured cell populations growing in cell culture and growing cell layers in early animal development. While cultured unstructured cell populations would apriori been classified as particularly suited for a biophysical approach since the degree to which they are committed to a genetic program is expected to be modest, early animal development would be expected to mark the other extreme—here the degree of determinism according to a genetic program would be expected to be very high. We consider a number of phenomena such as the growth kinetics and spatial structure formation of monolayers and multicellular spheroids, the effect of the presence of another cell type surrounding the growing cell population, the effect of mutations and the critical surface dynamics of monolayers. Different from unstructured cell populations, cells in early development and at tissue interfaces usually form highly organized structures. An example are tissue layers. Under certain circumstances such layers are observed to fold. We show that folding pattern again can largely be explained by physical mechanisms either by a buckling instability or active cell shape changes. The paper combines new and published material and aims at an overview of a wide range of physical aspects in unstructured populations and growing tissue layers.     

Object characterization with refractometric digital Fourier holography

We demonstrate a digital holographic method in which two different substances in a blend are discerned. The method requires only one set of exposures and one reconstruction in the plane of focus. The phase is unwrapped by Flynn's discontinuity algorithm to produce an image of the variation of the optical distance of the illuminating wave. Objects with indices of refraction that are higher and lower than the mounting liquid are detected as regions in which the phase is increased and decreased, respectively. We also present a method for calculating the volume distribution of substrates in a sample. The method is experimentally demonstrated with crystals of NaCl and KCl.     

Alpha-gamma decay studies of $$^{247}$$ Md

The European Physical Journal A - The goal of the present paper is twofold. First, a novel expansion many-body method applicable to superfluid open-shell nuclei, the so-called Bogoliubov in-medium...     

Interference and interactions in mesoscopic rings

We consider a mesoscopic ring connected to external reservoirs by tunnel junctions. The ring is capacitively coupled to an external gate electrode and may be pierced by a magnetic field. Due to strong electron–electron interactions within the ring the conductance shows Coulomb blockade oscillations as a function of the gate voltage, while Aharonov–Bohm interference effects lead to a dependence on the magnetic flux. The Hamiltonian of the ring is given by a Luttinger model that allows for an exact treatment of both interaction and interference effects. We conclude that the positions of conductance maxima as a function the external parameters can be used to determine the interaction parameter , and the shapes of conductance peaks are strongly affected by electron correlations within the ring.     

钨离子团簇与N2分子的反应性

利用激光蒸发团簇源产生Wn团簇束,团簇束通过一个充有N2气体分 子的低压反应池,利用飞行时间质谱探测反应产物,在类单次碰撞条件下研究了W+10 -W+50和N2分子的反应性,在室温条件下测量了N2分子与W+n团簇反应的 反应几率。团簇尺寸在10～26原子的团簇与N2分子的反应几率与团簇尺寸有很强的相关性 ,对n=16,22,23的团簇具有比较高的反应性。W+n与N2分子的反应性与Wn与N 2分子的反应性显示出相似的规律性。     

Quantum critical dynamics simulation of dirty boson systems

Recently, the scaling result z=d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte?Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z=1.8±0.05, ν=1.15±0.03, and η=-0.3±0.1, hence suggesting that z=2 is not satisfied.     

Field evaporation of silicon surfaces

Quantitative measurements on field evaporation of Si(111) surfaces in hydrogen imaging gas have been carried out by field ion microscopy. The field evaporation rate is found to increase exponentially with increase of the reciprocal of tip temperature in the range 80–103 K. The evaporation field strength increases with increase of tip temperature in the investigated range, 80–300 K. Within the applied pressure range, 5× 10^?6 to 2 × 10^?4 Torr of hydrogen gas, the evaporation rate linearly increases with the gas pressure. Similar effects of temperature and gas pressure on field evaporation of Si(111) surfaces have been observed also in silane imaging gas. A model, based on a field-induced formation of surface hydrides as a rate-determining step, is proposed, which accounts for all the experimental results of the field evaporation process.     

Optical microscopic,X-ray diffraction,and electrical resistance studies of CuCl at high pressure

Electrical resistance and X-ray diffraction measurements and also optical observations under a polarizing microscope were made on CuCl to pressures in excess of 12.5 GPa at room temperature using a diamond anvil cell. Resistance measurements were also performed in a piston-cylinder apparatus to pressures of approximately 5.5 GPa at room temperature. Three samples of CuCl prepared by different methods were examined. No anomalous pressure dependence in electrical resistance was found in the pressure range studied, and no dramatic changes in optical transmission were observed up to pressures of approximately 10.0 GPa. Optical observations and X-ray diffraction measurements indicate the existence of four phases in the pressure range studied, including a nonconducting black opaque phase which grows with time when CuCl is left for several days at the highest pressures.     

A theoretical study of the copper–cysteine bond in blue copper proteins

 The accuracy of theoretical calculations on models of the blue copper proteins is investigated using density functional theory (DFT) Becke's three-parameter hybrid method with the Lee–Yang–Parr correlation functional (B3LYP) and medium-sized basis sets. Increasing the basis set to triple-zeta quality with f-type functions on all heavy atoms and enlarging the model [up to Cu(imidazole-CH₃)₂(SC₂H₅) (CH₃SC₂H₅)^0/+] has only a limited influence on geometries and relative energies. Comparative calculations with more accurate wave-function–based methods (second-order M?ller–Plesset perturbation theory, complete-active-space second-order perturbation theory, coupled-cluster method, including single and double replacement amplitudes and in addition triple replacement perturbatively) and a variety of basis sets on smaller models indicate that the DFT/B3LYP approach gives reliable results with only a small basis set dependence, whereas the former methods strongly depend on the size of the basis sets. The effect of performing the geometry optimizations in a continuum solvent is quite small, except for the flexible Cu-S_Met bond. The results of this study confirm the earlier results that neither the oxidized nor the reduced copper site in the blue proteins is strained to any significant degree (in energy terms) by the protein surrounding. Received: 7 July 2000 / Accepted: 17 November 2000 / Published online: 21 March 2001     

Simple synthesis of endo-2-bromo-5-thiabicyclo[2.1.1]hexane

A brief synthesis of endo-2-bromo-5-thiabicyclo [2.1.1]hexane ( 9 ) has been developed involving conversion of 3-cyclopentenol ( 6 ) to 3-thioacetoxycyclopentene ( 7 ), bromination of this giving trans-1,2-dibromo-4-thioacetoxycyclopentane ( 8 ), and treatment of the latter with base. Compound 9 is oxidized to its S-oxide 10 and S, S-dioxide 11 . Comparative ¹³C and ¹H NMR data are given for 9–11 .