Pulse polarography: IX. Proton diffusion in aqueous sulphate solution

Average diffusion currents, , of the ions H₃O⁺ and HSO₄^? in the system 0.1 M K₂SO₄+H₂SO₄ (pH=3.1?3.8) have been measured at 25°C both with a dropping mercury and a rotating disk electrode, using pulse techniques. The separate diffusion coefficients D_HSO4 and D_H have been estimated fromand it was found that D_H≤61×10^?6 cm²s^?1, which is definitely less than the value calculated when relaxation and (bulk) viscosity effects are taken into account. This is at variance with all the literature D_H values for non-sulphate systems and also with our experimental result D_H=(84.6±0.2)10^?6 cm²s^?1 for the system 0.1 M KCl+HCl, which is about 7% above the value from Onsager's theory. The peculiar behaviour of D_H in a K₂SO₄ solution is attributed to a strong decrease in rotational freedom of water molecules in such a medium.This paper also gives a critical evaluation of the principle of “independent diffusion” in excess neutral electrolyte if more than one species participates in the diffusion process.     

The rotational predissociation of the CH4+ and CD4+ ions

The metastable transitions producing CH₃³/CH₄ and CD₃⁺/CD₄ have been investigated by means of translational spectroscopy. For the first time structures are observed in a metastable peak corresponding to the dissociation of a polyatomic ion. They are interpreted by tunneling through a rotational barrier from discrete quasi-bound states. Kinetic energy releases have been measured.     

Viscosity of aqueous solutions of univalent electrolytes from 5 to 95°C

Viscosity measurements of a series of univalent electrolytes in water have been performed with an automatic dual viscometer system, covering the temperature range of 5 to 95°C. Results are discussed in terms of Jones-DoleB andD coefficients. TheB coefficients of the salts are divided into their ionic contributions according toB(K⁺)=B(Cl^–) at all temperatures. On a simple model intrinsic and structural contributions inB are calculated for the different ions. The structural term depends exponentially on the temperature in a unique manner, independent of the ion (except for Li⁺).     

Exact solution of the one-dimensional time-dependent Schrödinger equation with a rectangular well/barrier potential and its applications

We obtain an exact one-dimensional time-dependent solution for a wave function ψ(x, t) of a particle moving in the presence of a rectangular well or barrier. We present the solution, which holds for both the well and the barrier, in terms of the integrals of elementary functions; it is the sum of forward- and backward-moving components of the wave packet. We consider and numerically visualize the relative contribution of these components and of their interference to the probability density |ψ(x, t)|² and the particle arrival time and dwell time for the narrow and broad energy (momentum) distributions of the initial Gaussian wave packet. We show that in the case of a broad initial wave packet, the quantum mechanical counterintuitive effect of the influence of the backward-moving components on the considered quantities becomes essential.     

An efficient approach for the isolation, identification and evaluation of antimicrobial plant components on an analytical scale, demonstrated by the example of Radix imperatoriae

Using Radix imperatoriae (the root of masterwort) as an example, we describe an efficient approach for the isolation, identification and evaluation of bioactive plant components on an analytical scale. The extraction of Radix imperatoriae with ethyl acetate was enhanced by the application of ultrasound oscillations. This rhizome extract was applied to three pathogenic bacteria (Bacillus cereus, Escherichia coli, and Staphylococcus aureus) to determine its antimicrobial activity. Disk diffusion was utilized to determine susceptibility. The extract components were separated using a series of chromatography approaches (semi-preparative RP-HPLC, or RP-HPLC on an analytical scale), followed by testing. All fractions were analyzed by LC-UV-ESI-MS and 600 MHz microcoil ¹H NMR spectroscopy. Among other findings, in the fraction with the highest antibacterial activity we were able to identify oxypeucedanin and oxypeucedanin hydrate. Subsequent analysis revealed that only oxypeucedanin hydrate had antibacterial activity, whereas oxypeucedanin itself was inactive at the concentrations applied. Furthermore, oxypeucedanin hydrate appears to be largely, or exclusively, a by-product of sample preparation, since it is either not synthesized by the plant as a second metabolite or is produced by it in only very small quantities.     

UV radiation as a potential driving force for zooplankton community structure in Patagonian lakes

This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.     

Dissociative ion-pair formation in collisions of fast potassium atoms with benzene and fluorobenzene

Using a crossed molecular-beam technique, electron transfer is studied in collisions of fast potassium atoms with benzene and fluorobenzene molecules. The negative fragment ions formed in the collision region are extracted by a pulsed voltage, and their masses and energy release distributions analyzed by a time-of-flight (TOF) method. The dominant fragment from C6H5F is F-. The phenyl ring fragments CH- and C2H- are also observed but with lower intensities. In the case of C6H6 the dominant anionic specie is C2H-. The kinetic-energy release distributions of the various fragments are derived from the width and shapes of the TOF peaks in the spectrum.     

Glasslike structure of globular proteins and the boson peak

Vibrational spectra of proteins and topologically disordered solids display a common anomaly at low frequencies, known as boson peak. We show that such feature in globular proteins can be deciphered in terms of an energy landscape picture, as it is for glassy systems. Exploiting the tools of Euclidean random matrix theory, we clarify the physical origin of such anomaly in terms of a mechanical instability of the system. As a natural explanation, we argue that such instability is relevant for proteins in order for their molecular functions to be optimally rooted in their structures.     

Real quadratic flexible division algebras

In this paper we give a new process called vectorial isotopy, in order to classify the eight-dimensional real quadratic flexible division algebras, and we solve the isomorphism problem.     

Determination of the emission rate of an Am–Be neutron source with a Bonner sphere spectrometer

The Neutron Measurements Laboratory of the Technical University of Madrid (LMN) has an automated panoramic irradiator with a 111 GBq ²⁴¹Am–Be neutron source installed in a bunker-type large room. This facility is going to be used for calibration purposes. Recently, a spectrometry campaign involving four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral unfolding codes was carried out. As part of these measurements the emission rate, B(t), was estimated. The application of the generalized fitting method to account for the scattering contribution is difficult due to specific characteristics of the neutron installation. A reduced fitting method, which includes room-return and in-scatter, has instead been used to overcome this problem.Detailed Monte Carlo simulations (with MCNPX code) were also performed to estimate the fluence rate using the measured source strength value. This was performed at different points. Results were then compared with measurements.Finally, the ambient dose equivalent rate measured with a neutron monitor (LB6411) was compared with results using the BSS.