Long-lived transient anion of c-C4F8O.

We report partial cross sections for electron attachment to c-C4F8O, a gas with promising technological applications in free-electron-rich environments. The dissociative electron attachment leads to a number of anionic fragments resulting from complex bond-breaking and bond-forming processes. However, the anion with the highest abundance is the non-dissociated (transient) parent anion which is formed around 0.9 eV electron energy. Its lifetime reaches tens of microseconds. We discuss the origin of this long lifetime, the anion's strong interactions with other molecules, and the consequences for electron-scavenging properties of c-C4F8O in denser environments, in particular for its use in mixtures with CO2 and N2.

Experimental evidence on the mechanism of dissociative electron attachment to formic acid.

Two mechanisms for dissociative electron attachment in HCOOH, the formation of HCOO(-)+H, were proposed in the literature: (i) via a direct electron attachment into a σ* resonance, augmented by dipole binding of the incident electron [G. A. Gallup et al., Phys. Rev. A 79, 042701 (2009)], and (ii) with the 1.8 eV π* resonance as a doorway state, linked to the products by symmetry lowering-distortion of the temporary anion, primarily the C-H bond, from the planar symmetry [T. N. Rescigno et al., Phys. Rev. Lett. 96, 213201 (2006)]. The later mechanism implies a reduction of the cross section upon deuteration of the hydrogen bonded to the C atom, whereas the former mechanism would leave the cross section unaffected. Our experimental absolute cross sections for the four isotopomers of formic acid show that deuteration on the C atom reduces the cross section value only marginally (by 12%) compared to deuteration on the O atom (reduction by a factor of 16), and thus favor mechanism (i).

Dispersion of light and heavy pollutants in urban scale models: CO(2) laser photoacoustic studies.

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO(2) laser photoacoustic spectroscopy in the region of the atmospheric window (9-10 mum). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

The role of leptin in human physiology and pathophysiology.

This review focuses on current knowledge of leptin biology and the role of leptin in various physiological and pathophysiological states. Leptin is involved in the regulation of body weight. Serum leptin can probably be considered as one of the best biological markers reflecting total body fat in both animals and humans. Obesity in man is accompanied by increased circulating leptin concentrations. Gender differences clearly exist. Leptin is not only correlated to a series of endocrine parameters such as insulin, glucocorticoids, thyroid hormones, testosterone, but it also seems to be involved in mediating some endocrine mechanisms (onset of puberty, insulin secretion) and diseases (obesity, polycystic ovary syndrome). It has also been suggested that leptin can act as a growth factor in the fetus and the neonate.

[New findings on the role of leptins in regulation of the reproductive system in humans]. / Nekteré nové poznatky o roli leptinu v regulaci reprodukcního systému cloveka.

The reproductive activity is closely related to the nutritional status of the organism. A new hormone--leptin has been discovered a few years ago, which informs the brain about fat supplies in the body. Leptin participates in the regulation of the reproductive system at both, peripheral and central, levels. There are discussions about leptin as a possible trigger of puberty. The prepubertal leptin levels are low in both sexes; they increase with the onset of puberty. It has been suggested that leptin resistance might exist in the childhood, allowing the onset of the puberty only at the moment, when the adipose stores are adequate for the strongly demanding period of the adolescence. The role of leptin in pathogenesis of polycystic ovary syndrome (PCOS) is studied. The significance of leptin during pregnancy and after birth remains still unclear.