Momentum profiles of the valence orbitals of methylpropane, also known as isobutane (CH3CH(CH3)CH3), have been studied by using a high resolution binary (e,2e) electron momentum spectrometer (EMS), at an impact energy of 1200 eV plus the binding energy, and using symmetric noncoplanar kinematics. The coincidence energy resolution of the EMS spectrometer is 0.95 eV full width at half-maximum. The experimental momentum profiles of the valence orbitals are compared with the theoretical momentum distributions calculated using Hartree–Fock (HF) and density functional theory (DFT) methods with the two basis sets of 6-31G and 6-311++G**. The B3LYP functionals are used for the DFT calculations. In general, the experimental momentum distributions are well described by the HF and DFT calculations. The pole strengths of the main ionization peaks from the orbitals in the inner valence are estimated.
Histone proteins protect cellular DNA from radiation damage. We find that arginine, a major component of histone proteins, protects DNA from lesions induced by lowenergy secondary electrons generated by radiation. Thin films of 7 ± 2, 12 ± 4, and 17 ± 4 nm thicknesses containing arginine−plasmid−DNA complexes in molar ratio of [Arg 2+ ]/[PO 4 − ] = 16 are irradiated in vacuum with 5 and 10 eV electrons. Damage yields are measured for base damages, cross-links, single-strand breaks (SSBs), double-strand breaks, and other clustered lesions. Most damage results from dissociative electron attachment. Absolute cross sections (ACSs) for all damage types are extracted from yields at different film thicknesses. Compared with bare DNA, these ACSs are reduced by factors of up to 4.4 in Arg−DNA complexes. SSB protection is the highest. Potentially lethal cluster lesions decrease by factors of up to 2.2. ACSs are critical input parameters in modeling radiation-induced damage and assessing protection factors under simulated cellular conditions.
In this study, the nucleus formation and bubble growth at beginning of boiling process in microchannels was investigated. Canonical molecular distribution was introduced to analyze characteristics of nucleate boiling when liquid molecular number is very small. The minimum bulk phase volume in which phase change was enable to occur was determined from thermodynamic theory of bubble formation in a superheated liquid and from the energy distribution of the molecules in the bulk phase at a given temperature and pressure. The comparison of the free energy decrease during nucleus formation on a flat wall and at a corner of walls indicates that nuclei more easily form at a corner than on a flat wall for wetting liquids. The experimental results demonstrated that the superheat temperature increased as diameter of microchannels decreased. The experimental measurements are in a quite agreement with theoretical predictions.
A visual study was conducted to investigate the evaporation and nucleate boiling of a water droplet on heated copper, aluminum, or stainless surfaces with temperature ranging from 50°C to 112°C. Using a high-speed video imaging system, the dynamical process of the evaporation of a droplet was recoded to measure the transient variation of its diameter, height, and contact angle. When the contact temperature was lower than the saturation temperature, the evaporation was in film evaporation regime, and the evaporation could be divided into two stages. When the surface temperature was higher than the saturation temperature, the nucleate boiling was observed. The dynamical behavior of nucleation, bubble dynamics droplet were detail observed and discussed. The linear relationships of the average heat flux vs. temperature of the heated surfaces were found to hold for both the film evaporation regime and nucleate boiling regime. The different slopes indicated their heat transfer mechanism was distinct, the heat flux decreased in the nucleate boiling regime more rapidly than in the film evaporation due to the strong interaction between the bubbles.
An experimental investigation was conducted to describe the oscillation behavior of water droplets on solid surfaces as air flew through over the droplets, and the dynamical process was recorded using a high-speed CCD. Two liquid drop oscillation modes, forward-backward and upward-downward, and their mutual conversion were visually observed. Accounting for the internal flow and pressure distribution inside a liquid drop, a phenomenological explanation was proposed to understand the oscillation characteristics of two modes and the mutual conversion mechanisms.
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