A New Route to Dithiocarbamates from Tertiary N-Methyl and N-Benzylamines

The sequential treatment of various tertiary N-methyl and N-benzylamines with carbon disulfide, and then with an alkyl halide in tetrahydrofuran gave the corresponding dithiocarbamates in good to excellent yields.     

Green up-conversion of Er3+ in KGd(WO4)2 crystals. Effects of sample orientation and erbium concentration

Pumping with infrared light resonant to the energy position of ⁴ I _11/2 and ⁴ I _9/2 multiplets respectively has excited green up-conversion of Er³⁺ in KGd(WO₄)₂ single crystal. At room temperature the maximum green-emission intensity is achieved by pumping with light polarized parallel to the C₂ symmetry axis of the crystal (//p) at 981 and 801.5 nm, while pumping with light parallel to the principal m axis (//m) has maximum up-conversion at 978.2, 806 and 800 nm. The emission is weakly polarized. The maximum of the emission peaks at 547.8 nm if the light is analyzed parallel to the C₂ axis or at 552.4 nm for light perpendicular to it. The largest emission intensity was achieved with an erbium concentration about 3×10²⁰ cm^-3. A schematic model of the up-conversion process is suggested. Received: 4 July 2000 / Published online: 22 November 2000     

Crystal growth,optical spectroscopy,and continuous-wave laser operation of Ho:KLu(WO4)2 crystals

We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO₄)₂ crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO₄)₂ by in-band pumping using a Tm:KLu(WO₄)₂ pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO₄)₂ laser.     

Fluorescence study of the dynamic interaction between E1(145–162) sequence of hepatitis GB virus C and liposomes

The physicochemical characterization of the peptide sequence E1(145–162) corresponding to the structural protein E1 of the hepatitis G virus was done by studying its interaction with model membranes. Small unilamellar vesicles (SUVs) of dimyristoylphosphatidylglycerol or dimyristoylphosphatidylcholine were chosen as mimetic membranes. Peptide incorporation and location in the phospholipid bilayer was investigated by fluorescence anisotropy with SUVs labeled with diphenylhexatriene (DPH) or trimethylammonium–DPH. The addition of the peptide E1(145–162) showed significant changes in the anisotropy values of the probe located at the air/water interface. These results indicate that the peptide E1(145–162) preferably interacts with the lipid surface without penetrating inside the bilayer. A series of fluorescence experiments based on tryptophan peptide fluorescence were modeled by means of multivariate curve resolution-alternating least squares (MCR-ALS) algorithm to further study the peptide interaction with bilayers at different temperatures. The preliminary results obtained with MCR-ALS showed how the peptide concentration decay is directly linked to the appearance of a new specie, which corresponds to the lipid-peptide binding. These results provide useful information for the design of synthetic immunopeptides that can be incorporated into a liposomal system with potential to promote a direct delivery of the membrane-incorporated immunogen to the immunocompetent cells, thus increasing the immuno response from the host. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The linear combination of vectors implies the existence of the cross and dot products

Given two vectors u and v, their cross product u × v is a vector perpendicular to u and v. The motivation for this property, however, is never addressed. Here we show that the existence of the cross and dot products and the perpendicularity property follow from the concept of linear combination, which does not involve products of vectors. For our proof we consider the plane generated by a linear combination of uand v. When looking for the coefficients in the linear combination required to reach a desired point on the plane, the solution involves the existence of a normal vector n = u × v. Our results have a bearing on the history of vector analysis, as a product similar to the cross product but without the perpendicularity requirement existed at the same time. These competing products originate in the work of two major nineteen-century mathematicians, W. Hamilton, and H. Grassmann. These historical aspects are discussed in some detail here. We also address certain aspects of the teaching of u × v to undergraduate students, which is known to carry some difficulties. This includes the algebraic and geometric denitions of u × v, the rule for the direction of u × v, and the pseudovectorial nature of u × v.     

$${{{\mathbb Z}_2}{{\mathbb Z}_4}}$$ -linear codes: generator matrices and duality

A code C{{\mathcal C}} is \mathbb Z₂\mathbb Z₄{{{\mathbb Z}_2}{{\mathbb Z}_4}} -additive if the set of coordinates can be partitioned into two subsets X and Y such that the punctured code of C{{\mathcal C}} by deleting the coordinates outside X (respectively, Y) is a binary linear code (respectively, a quaternary linear code). In this paper \mathbb Z₂\mathbb Z₄{{{\mathbb Z}_2}{{\mathbb Z}_4}} -additive codes are studied. Their corresponding binary images, via the Gray map, are \mathbb Z₂\mathbb Z₄{{{\mathbb Z}_2}{{\mathbb Z}_4}} -linear codes, which seem to be a very distinguished class of binary group codes. As for binary and quaternary linear codes, for these codes the fundamental parameters are found and standard forms for generator and parity-check matrices are given. In order to do this, the appropriate concept of duality for \mathbb Z₂\mathbb Z₄{{{\mathbb Z}_2}{{\mathbb Z}_4}} -additive codes is defined and the parameters of their dual codes are computed.