Radiative kinks and fermionic zero modes in a (λφ6)1+1 model

We consider bidimensional scalar models including kink solutions _k (x). Using the hidden supersymmetric properties of the Dirac equation, we describe a general method to find normalizable fermionic zero modes. In particular, we apply the technique to a ( ⁶)₁₊₁ model. Going to the one-loop order of the effective potential, the emergence of a radiative kink provides an interesting scalar background in order to discuss the Dirac equation.     

Hydrogenated amorphous silicon films obtained by a low pressure dc glow discharge

Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH₄ with electrostatic confinement at a pressure as low as 0.4 Pa. The plasma used is quite quiescent as has been observed by means of reproducible Langmuir probe measurements. Substrates have been placed at different locations in between the electrodes, some of them facing the anode and the others facing the cathode.Films deposited on substrates facing the cathode present a granular, non-columnar, structure, an IR spectrum with only SiH absorption peaks, and a very low photoresponse. Films deposited on substrates facing the anode have a similar IR spectrum but are homogeneous, have lower hydrogen content, and present a high photoresponse. The optical absorption coefficient shows in all samples thenE=C(E–E₀) ^x behaviour, but with exponentx=3 and notx=2 as is usually considered in a-SiH.     

Lanthanide modulation of the orientation of macromolecules induced by purple membrane.

Addition of Tb3+ to purple membrane (PM) suspensions changes the orientation of the menbrane normal from parallel to perpendicular with respect to the magnetic field. Residual dipolar couplings measured in protein L in the presence of PM are scaled by a factor of -1/2. NMR line broadening and cross-correlation effects induced by the addition of PM are partially reversed by Tb3+ but not by Tm3+ that has no effect on the orientation of PM. This is interpreted as the result of anisotropically restricted motion of protein L in the transiently PM-bound form.     

First synthesis of pyrrolothiadiazinones. An alternative core ring for xanthine based structures

The first synthesis of pyrrolothiadiazine core ring bearing substituents at positions 1, 3 and 6 is described, using a straightforward synthesis from diversely substituted 5-methylthiadiazines. These structures are of interest not only because they can be considered as useful building blocks but also because they can potentially be used as alternative core rings for biologically important molecules bearing xanthine as a central core.     

Determination of liposoluble vitamins in cooked meals, milk and milk products by liquid chromatography

A method for the simultaneous determination of liposoluble vitamins in cooked meals was established. Saponification was performed with 50% (w/v) KOH at 80 degrees C, and ascorbic acid was added as antioxidant. The subsequent extraction was carried out with diethyl ether. This was followed by a liquid chromatographic separation on a reversed-phase C18 column with methanol-water (94:6, v/v as the mobile phase. Retinyl acetate was used as the internal standard. The analytical parameters linearity, detection limit (0.19 and 8.33 microg/100 g for retinol and alpha-tocopherol, respectively), precision of the method (RSD=5.24 and 6.99% for retinol and alpha-tocopherol, respectively) and recovery assays (95.6 and 96.5% for retinol and alpha-tocopherol, respectively) show that the method studied is useful for measuring these compounds in foods and cooked meals.     

Curve-fitting overlapped bands: quantification and improvement of curve-fitting robustness in the presence of errors in the model and in the data

Estimation of the band parameters of overlapped bands often relies on curve-fitting. It has been demonstrated that curve-fitting provides the maximum likelihood estimation of band parameters under a series of assumptions. One of these assumptions is that the curve-fitting model is correct and any error in the data is random. Under real conditions, we have to acknowledge the unavoidable presence of errors in the model and systematic errors in the data. Here, we derive an expression for the estimation of how these errors affect the quality of the parameters obtained from curve-fitting. In addition, we derive theoretical expressions to quantify the extent to which different methods can improve the curve-fitting robustness to these errors. The methods considered are: (i) deterministic and (ii) probabilistic constraints in the band parameters, (iii) curve-fitting band-narrowed data, and (iv) building a more accurate model. The theoretical expressions obtained are tested in the curve-fitting of a synthetic noisy spectrum with either baseline or band shape errors, and in the curve-fitting of the experimental infrared amide I band of the membrane protein bacteriorhodopsin.     

Evaluation of the complexity of charge recombination kinetics in photosynthetic bacteria

Abstract Improvements in instrumentation and methodology have allowed us to collect data of high signal to noise and reliability on the kinetics of recovery of both light-induced absorbance changes and ESR signals at 95 K. The results obtained by the two methods are identical and can not be fit with a single exponential curve. The decay kinetics can be fit well with three exponential components which represent 85, 9 and 6% of the total change with rate constants of 29 s⁻¹, 69 s⁻¹ and 2.3 s⁻¹, respectively. An interesting effect by molecular oxygen on the relaxation time of the donor cation radical was found by ESR measurements at low temperatures and higher microwave power. This interaction with oxygen could be blocked by addition of small amounts (e.g. 0.05%) of organic solvents such as ethanol. A variety of systems were examined including R. rubrum whole cells and chromatophores prepared from R. rubrum and Rps. sphaeroides. R. rubrum chromatophore samples were examined at high and low light intensities, at pH values from 6 to 10, in the presence and absence of air and after equilibration in D₂O media. In all cases, the same decay kinetics were observed. It seems possible that the observed complex decay may be a characteristic of phototraps of all photosynthetic material and reflect fundamental structural and functional features yet to be uncovered.