First observation of 54Zn and its decay by two-proton emission

The nucleus 54Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasifragmentation of a 58Ni beam at 74.5 MeV/nucleon in a (nat)Ni target. The fragments were analyzed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54Zn implantation events were observed. From the correlated decay events, the half-life of 54Zn is determined to be 3.2(+1.8)(-0.8) ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial half-life are compared to model predictions and allow for a test of these two-proton decay models.     

Synthesis of optical standard frequencies in the S, C and L telecommunication bands by use of four-wave mixing in semiconductor optical amplifiers

The generation of standard reference frequencies close to the ITU channels is essential for the calibration and maintenance of DWDM systems. This work describes a method to synthesize frequency references in the range from 187.1 to 205.1 THz (1462-1602 nm). The method is based on the generation of four equispaced frequencies (by the process of four-wave mixing in a semiconductor amplifier) of which two are locked to absorption lines of the acetylene ¹²C₂H₂ (1511-1542 nm).     

Ring intermittency in coupled chaotic oscillators at the boundary of phase synchronization

A new type of intermittent behavior is described to occur near the boundary of the phase synchronization regime of coupled chaotic oscillators. This mechanism, called ring intermittency, arises for sufficiently high initial mismatches in the frequencies of the two coupled systems. The laws for both the distribution and the mean length of the laminar phases versus the coupling strength are analytically deduced. Very good agreement between the theoretical results and the numerically calculated data is shown. We discuss how this mechanism is expected to take place in other relevant physical circumstances.     

Synthesis and characterization of hollow ��-Fe2O3 sub-micron spheres prepared by sol�Cgel

In this work we report the preparation of magnetic hematite hollow sub-micron spheres (??-Fe₂O₃) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO₃)₃·9H₂O) particles in citric acid solution by following the sol?Cgel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM).     

Iron–cobalt nanocrystalline alloy supported on a cubic mesostructured silica matrix: FeCo/SBA-16 porous nanocomposites

A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal stability. Low-angle X-ray diffraction, N₂ physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction in H₂ flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix and they seem in a large extent to be allocated inside the pores.     

EPR spectroscopy of protein microcrystals oriented in a liquid crystalline polymer medium

Correlation of the g-tensor of a paramagnetic active center of a protein with its structure provides a unique experimental information on the electronic structure of the metal site. To address this problem, we made solid films containing metalloprotein (Desulfovibrio gigas cytochrome c(3)) microcrystals. The microcrystals in a liquid crystalline polymer medium (water/hydroxypropylcellulose) were partially aligned by a shear flow. A strong orientation effect of the metalloprotein was observed by EPR spectroscopy and polarizing optical microscopy. The EPR spectra of partially oriented samples were simulated, allowing for molecular orientation distribution function determination. The observed effect results in enhanced sensitivity and resolution of the EPR spectra and provides a new approach towards the correlation of spectroscopic data, obtained by EPR or some other technique, with the three-dimensional structure of a protein or a model compound.     

Comparison of CID, ETD and metastable atom-activated dissociation (MAD) of doubly and triply charged phosphorylated tau peptides

The fragmentation behavior of the 2+ and 3+ charge states of eleven different phosphorylated tau peptides was studied using collision-induced dissociation (CID), electron transfer dissociation (ETD) and metastable atom-activated dissociation (MAD). The synthetic peptides studied contain up to two known phosphorylation sites on serine or threonine residues, at least two basic residues, and between four and eight potential sites of phosphorylation. CID produced mainly b-/y-type ions with abundant neutral losses of the phosphorylation modification. ETD produced c-/z-type ions in highest abundance but also showed numerous y-type ions at a frequency about 50% that of the z-type ions. The major peaks observed in the ETD spectra correspond to the charge-reduced product ions and small neutral losses from the charge-reduced peaks. ETD of the 2+ charge state of each peptide generally produced fewer backbone cleavages than the 3+ charge state, consistent with previous reports. Regardless of charge state, MAD achieved more extensive backbone cleavage than CID or ETD, while retaining the modification(s) in most cases. In all but one case, unambiguous modification site determination was achieved with MAD. MAD produced 15-20% better sequence coverage than CID and ETD for both the 2+ and 3+ charge states and very different fragmentation products indicating that the mechanism of fragmentation in MAD is unique and complementary to CID and ETD.     

Estimation of free copper ion concentrations in blood serum using T(1) relaxation rates

The water proton relaxation rate constant R(1)=1/T(1) (at 60 MHz) of blood serum is substantially increased by the presence of free Cu2+ ions at concentrations above normal physiological levels. Addition of chelating agents to serum containing paramagnetic Cu2+ nulls this effect. This was demonstrated by looking at the effect of adding a chelating agent-D-penicillamine (D-PEN) to CuSO4 and CuCl2 aqueous solutions as well as to rabbit blood serum. We propose that the measurement of water proton spin-lattice relaxation rate constants before and after chelation may be used as an alternative approach for monitoring the presence of free copper ions in blood serum. This method may be used in the diagnosis of some diseases (leukaemia, liver diseases and particularly Wilson's disease) because, in contrast to conventional methods like spectrophotometry which records the total number of both bound and free ions, the proton relaxation technique is sensitive solely to free paramagnetic ions dissolved in blood serum. The change in R(1) upon chelation was found to be less than 0.06 s(-1) for serum from healthy subjects but greater than 0.06 s(-1) for serum from untreated Wilson's patients.