Thermal conductivity of isotopically enriched Si: revisited

The thermal conductivity of isotopically enriched ²⁸Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of four samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched ²⁸Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10±2%. This finding is in disagreement with an earlier report by Ruf et al. At ∼26 K the thermal conductivity of ²⁸Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of ∼8 for a 99.982% ²⁸Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be ∼3% lower than the values recommended in the literature.     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

A review of aspects relating to the improvement of holographic memory technology

Results of studying a holographic memory to write/read digital data pages are presented. The research has been carried out in Novosibirsk, Russia. Great attention was paid to methods of improving recording density and the reliability of data reading, the development of ‘dry’ photopolymers that provide recording of superimposed three-dimensional phase holograms, and the designing of parallel optic input large-scale integration (LSI) for reading and logical processing of data arriving from the holographic memory.     

Structural characterization of nano-crystalline Co3O4 ultra-fine fibers obtained by sol–gel electrospinning

In this paper, we report the obtention of ultrafine fibers of cobalt oxide (Co₃O₄) by combining electrospinning method with high-temperature calcinations from the precursor sol of poly(2-ethyl-2-oxazoline) (PEtOx)/cobalt acetate tetrahydrate [Co(CH₃COO)₂·4H₂O] in water. The optimum electrospinning conditions for obtaining precursor composite nanofibers from PEtOx/Co(CH₃COO)₂·4H₂O solution in water, to produce ceramic nanofibers, were studied. The average fiber diameter of the precursor composite fibers measured by scanning electron microscopy (SEM) was approximately 200 nm. Thermogravimetric analysis of PEtOx was performed to estimate the suitable calcination temperature of the precursor fibers. SEM images of the ceramic fibers obtained after calcination revealed the shrinkage in diameter due to complete degradation of the polymer and Co(CH₃COO)₂·4H₂O. Fourier transform infrared spectroscopy was used to ensure the complete pyrolysis of polymer during calcinations of the composite fibers. Crystalline properties of the ceramic fibers were studied by X-ray diffraction and high resolution transmission electron microscopy. The ceramic fibers are polycrystalline with an average grain size of ≈40 nm obtained at a calcination temperature of 773 K. It was observed that the grain sizes increased as the calcination temperature was increased, due to self assembly mechanism.     

The [Ru(CN)5(pyS)](4-) complex, an efficient self-assembled monolayer for the cytochrome c heterogeneous electron transfer studies

The organothiol 4-mercaptopyridine (pyS) has been used extensively as facilitator for the assessment of heterogeneous electron transfer reaction of cytochrome c (cyt c). Its efficiency, however, is strongly affected by the instability of the adlayer due to the C-S bond cleavage. The K(4)[Ru(CN)(5)(pyS)].3H(2)O complex was synthesized and characterized aiming its utilization as an inorganic self-assembled monolayer (SAM) that would enhance the gold adlayer stability. The SAM formed by this complex onto gold (RupySAu) was characterized by spectroscopic (FTIRRAS and SERS) and electrochemical (LSV) techniques. The ex situ vibrational SERS and FTIRRAS spectra data of this SAM formed onto gold suggest a sigma interaction between the gold and sulfur atoms of the complex, inducing a perpendicular arrangement in relation to the surface normal. Additionally, SERS and FTIRRAS spectra performed for freshly prepared RupySAu adlayer and for large immersion times in the precursor solution have not shown any significant change that would reflect the degradation of the adlayer. The LSV desorption curves of this SAM indicate an enhancement in the C-S bond strength of the pyS ligand when coordinated to the [Ru(CN)(5)](3-) moiety. Comparatively to the data obtained for the desorption process of the pyS monolayer, the reductive desorption potential, E(rd), of the RupySAu presents a shift of -17 mV. This bond strength intensification leads to an increase in the stability of the monolayer. The voltammetric curves of cyt c carried out with the RupySAu electrode showed electrochemical parameters consistent with those reported for the native protein, as well as the maintenance of the electrochemical kinetic data after repetitive cycles. The results all together suggest that the pi back-bonding effect from the [Ru(CN)(5)](3-) metal center plays an important role in the stability of the RupySAu adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction.     

Thermal conductivity of the single-crystal monoisotopic 29Si in the temperature range 2.4–410 K

Physics of the Solid State - The temperature dependence of the thermal conductivity κ(T) of single-crystal silicon highly enriched in 29Si (99.919%) isotope has been measured in the...     

Investigations into beam monitors at the AEg ̄ IS experiment

Detailed diagnostic of antiproton beams at low energies is required for essentially all experiments at the Antiproton Decelerator (AD), but will be particularly important for the future Extra Low ENergy Antiproton ring (ELENA) and its keV beam lines to the different experiments. Many monitors have been successfully developed and operated at the AD, but in particular beam profile monitoring remains a challenge. A dedicated beam instrumentation and detector test stand has recently been setup at the AE \(\bar {g}\) IS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Located behind the actual experiment, it allows for parasitic use of the antiproton beam at different energies for testing and calibration. With the aim to explore and validate different candidate technologies for future low energy beam lines, as well as the downstream antihydrogen detector in AE \(\bar {g}\) IS, measurements have been carried out using Silicon strip and pixel detectors, a purpose-built secondary emission monitor and emulsions. Here, results from measurements and characterization of the different detector types with regard to their future use at the AD complex are presented.     

Thermophysical properties and crystal structure of high-purity monoisotopic <Superscript>80</Superscript>Se

The thermophysical and structural characteristics of high-purity monoisotopic ⁸⁰Se containing 99.9 at % main isotope were studied. Differences were found in properties between monoisotopic selenium and selenium of the natural abundance of isotopes, which had comparable chemical purities and identical thermal histories.     

Heat capacity of isotopically enriched Si, Si and Si in the temperature range 4 K<T<100 K

The heat capacity of isotopically enriched ²⁸Si, ²⁹Si, ³⁰Si samples has been measured in the temperature range between 4 and 100 K. The heat capacity of Si increases with isotopic mass. The values of the initial Debye temperature Θ_D(0) for the three isotopic varieties of silicon have been determined. Good agreement with the theoretical dependence of the heat capacity on isotopic mass has been found.