Intense slow beams of bosonic potassium isotopes

We report on an experimental realization of a two-dimensional magneto-optical trap (2D-MOT) that allows the generation of cold atomic beams of 39K and 41K bosonic potassium isotopes. The high measured fluxes up to 1.0x10^11 atoms/s and low atomic velocities around 33 m/s are well suited for a fast and reliable 3D-MOT loading, a basilar feature for new generation experiments on Bose-Einstein condensation of dilute atomic samples. We also present a simple multilevel theoretical model for the calculation of the light-induced force acting on an atom moving in a MOT. The model gives a good agreement between predicted and measured flux and velocity values for our 2D-MOT.Comment: Updated references, 1 figure added, 10 pages, 9 figure

Collisional properties of sympathetically cooled 39^{39}K

We report the experimental evidence of the sympathetic cooling of $^{39}$K with $^{87}$Rb down to 1 $\mu$K, obtained in a novel tight confining magnetic trap. This allowed us to perform the first direct measurement of the elastic cross section of $^{39}$K below 50 $\mu$K. The result obtained for the triplet scattering length, $a_T = -51(7)$ Bohr radii, agrees with previous results derived from photoassociation spectra and from Feshbach spectroscopy of $^{40}$K.Comment: 7 pages, 4 figures, submitted to Phys. Rev.

Uso da RMN no Estudo da Despolimerização de Poliuretanos Rígidos

Os poliuretanos (PUs) vem sendo utilizados cada vez mais em diversos setores do comércio. Com isso, grande quantidade de resíduos são gerados e precisam ser descartados de forma correta. As pesquisas neste campo vêm auxiliando indústrias a aplicarem processos de reciclagem que sejam baratos e com bons rendimentos. Neste trabalho, realizou-se a glicólise de um PU rígido empregando-se diferentes catalisadores. Os catalisadores utilizados foram: um tensoativo (CTAB), o NaOH, dois líquidos iônicos (tricloromanganato de 1-butil-3-metilimidazol e triclorozincato de 1-butil-3-metilimidazol), e quatro sais de Nióbios (óxido de nióbio, óxido de nióbio hidratado, cloreto de nióbio e oxalato amoniacal de nióbio). A técnica de RMN de 1H foi utilizada para a determinação da taxa de despolimerização do PU. Também foi utilizada a técnica RMN de 1H ordenada pela difusão (DOSY), que auxiliou na identificação da composição da mistura do produto. Na glicólise, foram testados glicerol (GCL) e dietileno glicol (DEG) como agente de glicólise. O PU foi sintetizado com a finalidade de se apresentar livre de aditivos no processo de despolimerização. A caracterização do PU foi feita por espectroscopia de infravermelho (FTIR) e de RMN de 1H. A taxa de conversão proporcionou sabermos qual catalisador tem melhor atividade catalítica. O NaOH como catalisador apresentou taxa de conversão de 100 % em 30 min de reação, como já é conhecido na literatura, e os espectros DOSY proporcionou observar produtos que não foram perceptíveis apenas pelo espectro de RMN de 1H. Os Líquidos Iônicos utilizados como catalisadores, apresentaram conversão de quase 80 % em 1h de reação, que podem ser melhorados modificando condições de reações. Os sais de Nióbio tiveram comportamento não catalítico, pois apresentaram taxa de conversão menor que a reação não catalisada. A RMN-DOSY indicou uma mistura complexa de subprodutos da reação, diferentemente do que os dados de RMN de 1H indicaram como sendo a formação de um subproduto simples com terminação de diamina

Effect of rhTSH on Lipids

Background: Subclinical hypothyroidism is associated with increased blood lipid levels. However, the exact role of thyrotropin (TSH) alone is not clear. In order to clarify this point, we analysed the acute effect of recombinant human TSH (rhTSH) administration on lipid levels. Methods: Sera of 27 premenopausal women with well-differentiated thyroid cancer were analysed. Patients that underwent a total thyroidectomy, ablation with I-131 (Iodine 131) and rhTSH administration as a part of routine follow-up American Thyroid Association guidelines were included. The protocol consists of 2 intramuscular injections of 0.9 mg of rhTSH, performed on day 1 day and day 2, with blood collection on day 1 (before rhTSH administration), and day 5. TSH, free thyroxine, total cholesterol, low-density lipoprotein cholesterol (LDLc), high density lipoprotein cholesterol (HDLc), and triglycerides were assessed in all the samples, before and four days after the first administration of rhTSH. Results: Total cholesterol and triglycerides significantly increased after stimulation of rhTSH (respectively, 192 +/- 33 vs. 207 +/- 26, p = 0.036 and 72 +/- 23 vs. 85 +/- 23, p = 0.016). LDLc and HDLc showed comparable concentrations before and after the test (respectively, 115 +/- 27 vs. 126 +/- 22, p = 0.066, and 62 +/- 15 vs. 64 +/- 15, p = 0.339), while non-HDLc increased after stimulation (130 +/- 30 vs. 143 +/- 25, p = 0.045). Conclusion: TSH has a direct effect on total cholesterol, triglycerides, and nonHDLc. Explanation of these phenomena will require additional studies

Band spectra of rectangular graph superlattices

We consider rectangular graph superlattices of sides l1, l2 with the wavefunction coupling at the junctions either of the delta type, when they are continuous and the sum of their derivatives is proportional to the common value at the junction with a coupling constant alpha, or the "delta-prime-S" type with the roles of functions and derivatives reversed; the latter corresponds to the situations where the junctions are realized by complicated geometric scatterers. We show that the band spectra have a hidden fractal structure with respect to the ratio theta := l1/l2. If the latter is an irrational badly approximable by rationals, delta lattices have no gaps in the weak-coupling case. We show that there is a quantization for the asymptotic critical values of alpha at which new gap series open, and explain it in terms of number-theoretic properties of theta. We also show how the irregularity is manifested in terms of Fermi-surface dependence on energy, and possible localization properties under influence of an external electric field. KEYWORDS: Schroedinger operators, graphs, band spectra, fractals, quasiperiodic systems, number-theoretic properties, contact interactions, delta coupling, delta-prime coupling.Comment: 16 pages, LaTe