Distributional and Classical Solutions to the Cauchy Boltzmann Problem for Soft Potentials with Integrable Angular Cross Section

This paper focuses on the study of existence and uniqueness of distributional and classical solutions to the Cauchy Boltzmann problem for the soft potential case assuming S ^n?1 integrability of the angular part of the collision kernel (Grad cut-off assumption). For this purpose we revisit the Kaniel–Shinbrot iteration technique to present an elementary proof of existence and uniqueness results that includes the large data near local Maxwellian regime with possibly infinite initial mass. We study the propagation of regularity using a recent estimate for the positive collision operator given in (Alonso et al. in Convolution inequalities for the Boltzmann collision operator. arXiv:0902.0507 [math.AP]) , by E. Carneiro and the authors, that allows us to show such propagation without additional conditions on the collision kernel. Finally, an L ^p -stability result (with 1≤p≤∞) is presented assuming the aforementioned condition.     

Molecular dynamics simulation of zirconia melting

The melting point for the tetragonal and cubic phases of zirconia (ZrO₂) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.     

Power-law time distribution of large earthquakes

We study the statistical properties of time distribution of seismicity in California by means of a new method of analysis, the diffusion entropy. We find that the distribution of time intervals between a large earthquake (the main shock of a given seismic sequence) and the next one does not obey Poisson statistics, as assumed by the current models. We prove that this distribution is an inverse power law with an exponent mu=2.06+/-0.01. We propose the long-range model, reproducing the main properties of the diffusion entropy and describing the seismic triggering mechanisms induced by large earthquakes.     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

Raman Spectroscopy Analysis of a Playing Card from the 18th Century

We present the characterization, by means of three complementary experimental techniques (optical microscopy [OM], scanning electron microscopy equipped with energy dispersive X-Ray spectroscopy [SEM-EDX], and micro-Raman spectroscopy [µRaman]), of a card belonging to a deck of the Spanish pattern made in Perú at the time of Virreinato de Perú (18th century). The objective is to obtain detailed information on the pictorial palette used for the decoration of the cards, where two basic colors, red and green, are seen. Small samples from both colored regions were analyzed.     

Vibrational Spectra of Dimethyldithiophosphinate Anion: (CH3)2PS2

Abstract

The infrared and Raman spectra of dimethyldithiophosphinate anion (CH₃)₂PS₂ were measured and the vibrational modes for the anion complex were assigned. A Normal Coordinate Analysis in the Modified General Valence Force Field (MGVFF) approximation was carried out assuming C_2v symmetry. Ab Initio Calculations at RHF and MP2 level were also carried out for the anion geometry as well as for its frequencies, intensities and force constants.     

Metabolic Profiling of Murine Macrophages Exposed to Silver Nanoparticles at Dose and Time Dependencies

The macrophage time-dependent metabolic profile changing basal metabolism triggered by nanoparticles can be obtained and used to improve wound healing treatments. Herein this study demonstrates that metabolic status responds systematically to cytotoxicity manipulation, providing an interesting way of cellular control. Nuclear magnetic resonance (NMR) based metabolomics and cytotoxic assays are used to study RAW 264.7 cells exposed to AgNPs at different concentrations and incubation times. Cytotoxicity data show a slight decrease in cellular expansion rates accompanied by morphological changes in cells. Metabolomics show that despite the glycolytic activity of treated and non-treated cells remains unchanged; however, only the treated cells present a rich Citrate environment signaling up-regulation of Tricarboxylic-Acid-Cycle (TCA). Cells choose aerobic routes instead of anaerobic ones to produce energy and self-regulate their amino acid metabolism to balance TCA. Choline metabolism is down-regulated once its sub-products, Betaine and Glycine, are reduced, thus compromising Creatine synthesis. Phospholipid metabolism is down-regulated due to the decreasing of Phosphocholine and Sn-Glycerol-3-PC, in agreement with the cytotoxicity results. Pyroglutamate decreases in treated cells, signaling different levels of oxidative stress. These analytical tools can characterize AgNPs-treatments, even distinguishing dose and time dependencies. Therefore, the fine-tuning of exposition parameters can modulate cellular activity to achieve better wound healing.     

Mechanistic Studies of the Photolysis of Phosphonium Salts

Abstract

As part of our continuing interest in the mechanistic photochemistry of phosphonium salts (Toscano et al., Chez. Commun., 567 (1973); J. Phys. Chem., 83(9), 1213 (1979)) we have investigated the photodecomposition (313 nm irradiation) of (1-naphthyl-methyl) triphenylphosphonium (I) chloride and tetrafluoroborate in deaerated isopropanol:     

Ammonium chloride salting out extraction/cleanup for trace-level quantitative analysis in food and biological matrices by flow injection tandem mass spectrometry

A sample extraction and purification procedure that uses ammonium-salt-induced acetonitrile/water phase separation was developed and demonstrated to be compatible with the recently reported method for pesticide residue analysis based on fast extraction and dilution flow injection mass spectrometry (FED-FI-MS). The ammonium salts evaluated were chloride, acetate, formate, carbonate, and sulfate. A mixture of NaCl and MgSO₄, salts used in the well-known QuEChERS method, was also tested for comparison. With thermal decomposition/evaporation temperature of <350 °C, ammonium salts resulted in negligible ion source residual under typical electrospray conditions, leading to consistent method performance and less instrument cleaning. Although all ammonium salts tested induced acetonitrile/water phase separation, NH₄Cl yielded the best performance, thus it was the preferred salting out agent. The NH₄Cl salting out method was successfully coupled with FI/MS/MS and tested for fourteen pesticide active ingredients: chlorantraniliprole, cyantraniliprole, chlorimuron ethyl, oxamyl, methomyl, sulfometuron methyl, chlorsulfuron, triflusulfuron methyl, azimsulfuron, flupyrsulfuron methyl, aminocyclopyrachlor, aminocyclopyrachlor methyl, diuron and hexazinone. A validation study was conducted with nine complex matrices: sorghum, rice, grapefruit, canola, milk, eggs, beef, urine and blood plasma. The method is applicable to all analytes, except aminocyclopyrachlor. The method was deemed appropriate for quantitative analysis in 114 out of 126 analyte/matrix cases tested (applicability rate = 0.90). The NH₄Cl salting out extraction/cleanup allowed expansion of FI/MS/MS for analysis in food of plant and animal origin, and body fluids with increased ruggedness and sensitivity, while maintaining high-throughput (run time = 30 s/sample). Limits of quantitation (LOQs) of 0.01 mg kg⁻¹ (ppm), the ‘well-accepted standard’ in pesticide residue analysis, were achieved in >80% of cases tested; while limits of detection (LODs) were typically in the range of 0.001–0.01 mg kg⁻¹ (ppm). A comparison to a well-established HPLC/MS/MS method was also conducted, yielding comparable results, thus confirming the suitability of NH₄Cl salting out FI/MS/MS for pesticide residue analysis.     

Non-linear parallel solver for detecting point sources in CMB maps using Bayesian techniques

In this work we present a suitable computational tool to deal with large matrices and solve systems of non-linear equations. This technique is applied to a very interesting problem: the detection and flux estimation of point sources in Cosmic Microwave Background (CMB) maps, which allows a good determination of CMB primordial fluctuations and leads to a better knowledge of the chemistry at the early stages of the Universe. The method uses previous information about the statistical properties of the sources, so that this knowledge is incorporated in a Bayesian scheme. Simulations show that our approach allows the detection of more sources than previous non-Bayesian techniques, with a small computation time.