Partition potential for hydrogen bonding in formic acid dimers

The ground-state energy and density of 4 low-energy conformations of the formic acid dimer were calculated via partition density functional theory (PDFT). The differences between isolated and PDFT monomer densities display similar deformation patterns for primary and secondary hydrogen bonds (HBs) among all 4 dimers. In contrast, the partition potential shows no transferable features in the bonding regions. These observations highlight the global character of the partition potential and the cooperative effect that occurs when a dimer is bound via more than 1 HB. We also provide numerical confirmation of the intuitive (but unproven) observation that fragment deformation energies are larger for systems with larger binding energies.     

TRPM5-expressing microvillous cells in the main olfactory epithelium

Background  

The main olfactory epithelium (MOE) in the nasal cavity detects a variety of air borne molecules that provide information regarding the presence of food, predators and other relevant social and environmental factors. Within the epithelium are ciliated sensory neurons, supporting cells, basal cells and microvillous cells, each of which is distinct in morphology and function. Arguably, the least understood, are the microvillous cells, a population of cells that are small in number and whose function is not known. We previously found that in a mouse strain in which the TRPM5 promoter drives expression of the green fluorescent protein (GFP), a population of ciliated olfactory sensory neurons (OSNs), as well as a population of cells displaying microvilli-like structures is labeled. Here we examined the morphology and immunocytochemical properties of these microvillous-like cells using immunocytochemical methods.     

Magnetic properties of the mechanically alloyed Fe0.9-xMn0.1Alx system

Samples of nominal composition Fe_0.9-xMn_0.1Al_x (0.1 ? x ? 0.5) were prepared by mechanical alloying starting from pure elements. Milling times of 24, 72 and 144 h were considered. The magnetic properties of the samples were studied by using ⁵⁷Fe Mössbauer spectroscopy, vibrating sample magnetometry and magnetic susceptibility measurements. The phase distribution was determined from X-ray diffractometry. The so obtained results evidence a strong dependence on the milling time and Al concentration of the room-temperature hyperfine field distributions and coercive forces. The susceptibility measurements in the range of temperature between 10 K and 180 K suggest the occurrence of different types of transitions as the temperature is increased: (a) from a ferromagnetic to a paramagnetic phase, (b) from a reentrant spin-glass phase to a ferromagnetic one and (c) from spin-glass to a paramagnetic phase. These transitions are also strongly influenced by the milling time and the Al concentration.     

Dimension Reduction for Systems with Slow Relaxation

Journal of Statistical Physics - We develop reduced, stochastic models for high dimensional, dissipative dynamical systems that relax very slowly to equilibrium and can encode long term memory. We...     

Hysteretic behavior of Fe0.9−qMn0.1Alq-disordered alloys: a Monte Carlo study

In this work we have simulated the Fe_0.9−qMn_0.1Al_q alloy series with Al contents ranging from 10 up to 50 at%, and for several system sizes. In the simulation, the atoms are randomly distributed on a body-centered cubic according to the atomic disorder achieved through quenching techniques for the experimental samples. In computing the thermodynamic quantities such as the magnetization per site as a function of an external applied magnetic field, we have employed a Monte Carlo algorithm based on a Metropolis dynamics implemented with a random site-diluted Ising model. In this model, we have taken into account nearest-neighbor interactions for which both the ferromagnetic (Fe–Fe) and antiferromagnetic (Fe–Mn, Mn–Mn) interactions are present. From the simulation of the hysteresis loops at room temperature, the remanence and the coercive force as a function of the Al concentration have been obtained. Finally, a comparison with the previous experimental data on coercivity obtained by means of vibrating sample magnetometry is also carried out and discussed.     

Thermally Driven and Ball-Milled Hematite to Magnetite Transformation

In this work, a study on the dynamics of transformation from hematite (α-Fe₂O₃) to magnetite (Fe₃O₄) by following two solid-state reaction methods is carried out. One of the procedures consists of a thermal treatment under a 20% H₂ and 80% N₂ atmosphere at 375°C, whereas the second method involves a planetary ball mill to induce the transformation. The phases evolution as a function of the thermal treatment time ranging from 0 up to 25 min every 2.5 min, and from 0 up to 6 hours every hour in the case of the milling method, was followed by using room-temperature Mössbauer spectroscopy and X-ray diffraction analysis. Results evidence a well-behaved structural transformation for which highly stoichiometric Fe₃O₄ as a single phase was obtained for treatment times above 12.5 min in the case of the thermally treated samples. Differently from this a less stoichiometric magnetite characterized by a distribution of hyperfine fields for milling times above 3 hours in the case of the ball milled samples was obtained. For reaction times below 12.5 min, two interpretation models based on the presence of an anion-deficient magnetite Fe₃O_4?δ and the presence of maghemite accounting for the intermediate states during the thermal transformation are also presented and discussed.

     

To mathematize, or not to mathematize chemistry

By analysing a contemporary criticism to the so called “mathematical chemistry”, we discuss what we understand by mathematizing chemistry and its implications. We then pass to ponder on some positions on the subject by considering the cases of Laszlo, Venel and Diderot, opponents to the idea of mathematization of chemistry. In contrast, we analyse some scholars’ ideas on the fruitful relationship between mathematics and chemistry; here Dirac and Brown are considered. Finally, we mention that the mathematical–chemistry relationship should be considered beyond the mere aspect of whether chemistry is or not able to be mathematized. This discussion is based upon opinions by Kant and Comte, the first one having two positions on chemistry based upon mathematics and the latter mooting the idea of doing chemistry with mathematical spirit.     

Tilted electric field effects on the electronic states in a GaAs quantum disk

In the present work we report the effects of a geometrical confinement and tilted applied electric field on the electronic energy levels in a semiconducting quantum disk. Calculations are performed in the effective mass approximation and using a variational method. The results can be summarized as follows: (1) due to the infinite confinement along the all directions of the heterostructure, the variational calculation with two parameters for tilted applied electric field can be treated with two independent each other variational parameters; (2) the magnitude of the energy shift is an increasing function of the applied electric field; (3) the effects of the applied electric field are magnified as the dimensions of the heterostructure (height and radius) grow; and finally (4) for large enough applied electric field the energy shift is a linear function of the applied electric field.