Towards absolute calibration of optical tweezers

Aiming at absolute force calibration of optical tweezers, following a critical review of proposed theoretical models, we present and test the results of MDSA (Mie-Debye-Spherical Aberration) theory, an extension of a previous (MD) model, taking account of spherical aberration at the glass/water interface. This first-principles theory is formulated entirely in terms of experimentally accessible parameters (none adjustable). Careful experimental tests of the MDSA theory, undertaken at two laboratories, with very different setups, are described. A detailed description is given of the procedures employed to measure laser beam waist, local beam power at the transparent microspheres trapped by the tweezers, microsphere radius and the trap transverse stiffness, as a function of radius and height in the (inverted microscope) sample chamber. We find generally very good agreement with MDSA theory predictions, for a wide size range, from the Rayleigh domain to large radii, including the values most often employed in practice, and at different chamber heights, both with objective overfilling and underfilling. The results asymptotically approach geometrical optics in the mean over size intervals, as they should, and this already happens for size parameters not much larger than unity. MDSA predictions for the trapping threshold, position of stiffness peak, stiffness variation with height, multiple equilibrium points and `hopping' effects among them are verified. Remaining discrepancies are ascribed to focus degradation, possibly arising from objective aberrations in the infrared, not yet included in MDSA theory.Comment: 15 pages, 20 figure

Exceptional structure of the dilute A3_3 model: E8_8 and E7_7 Rogers--Ramanujan identities

The dilute A$_3$ lattice model in regime 2 is in the universality class of the Ising model in a magnetic field. Here we establish directly the existence of an E$_8$ structure in the dilute A$_3$ model in this regime by expressing the 1-dimensional configuration sums in terms of fermionic sums which explicitly involve the E$_8$ root system. In the thermodynamic limit, these polynomial identities yield a proof of the E$_8$ Rogers--Ramanujan identity recently conjectured by Kedem {\em et al}. The polynomial identities also apply to regime 3, which is obtained by transforming the modular parameter by $q\to 1/q$. In this case we find an A_1\times\mbox{E}_7 structure and prove a Rogers--Ramanujan identity of A_1\times\mbox{E}_7 type. Finally, in the critical $q\to 1$ limit, we give some intriguing expressions for the number of $L$-step paths on the A$_3$ Dynkin diagram with tadpoles in terms of the E$_8$ Cartan matrix. All our findings confirm the E$_8$ and E$_7$ structure of the dilute A$_3$ model found recently by means of the thermodynamic Bethe Ansatz.Comment: 9 pages, 1 postscript figur

Avaliação do período de floração e frutificação do banco ativo de germoplasma do jaborandi.

O jaborandi (Pilocarpus microphyllus Stapf ex wardleworth) pertencente à família Rutaceae está entre as plantas com efeito medicinal comprovado, sendo considerada uma espécie prioritária em programas de conservação. O Banco Ativo de Germoplasma (BAG) do jaborandi foi estabelecido em 1992, no Horto de Plantas Medicinais da EMBRAPA Amazônia Oriental, ano em que o jaborandi entrou na lista do IBAMA de espécies ameaçadas de extinção. Através do acompanhamento diário dessa espécie, foi possível avaliar o seu período de floração e frutificação no período de 2009 a 2010, buscando conhecer o melhor momento para a coleta de material vegetal. O BAG jaborandi teve floração e frutificação durante todo o período avaliado. O mês de setembro de 2010 foi o mês com maior número de dias de floração e o menor o mês de novembro de 2009. Os meses de abril e julho de 2009 e maio, junho e julho de 2010 foram os meses que apresentaram o maior número de acessos floridos. Quanto à frutificação, setembro de 2010 foi o mês onde ocorreu o maior número de dias de frutificação e o mês de junho de 2009 foi o menor. O maior número de acessos que frutificaram ocorreu nos meses de maio e julho de 2009 e maio, junho e julho de 2010.PIBIC-2011

Avaliação da regeneração de ramos de jaborandi (Pilocarpus microphyllus Stapf ex wardleworth).

Entre as plantas que possuem efeito medicinal comprovado, o jaborandi (Pilocarpus microphyllus Stapf ex wardleworth) é considerado planta obrigatória em programas de conservação. Das folhas, são extraídas sais de pilocarpina, cuja principal ação ocorre no tratamento contra o glaucoma. Nesse sentido, estudos relacionados com a regeneração de ramos de jaborandi são fundamentais no manejo para a colheita de folhas dessa espécie. Os acessos avaliados na pesquisa foram: Maisa, Merck cultivado a pleno sol e Merck cultivado à sombra; foram utilizados dois tipos de corte nos ramos, respectivamente, a 10 e 20 cm das bifurcações dos ramos. O acesso Merck cultivado a pleno sol obteve maiores resultado em relação ao número de folíolos e comprimento da brotação na altura de corte de 10 cm. Na altura de corte de 20 cm, o maior número de folíolos foi obtido pelos acessos Merck cultivado a pleno sol e na sombra e em relação ao comprimento da brotação o acesso, que sobressaio sobre os demais foi o Merck cultivado a pleno sol.PIBIC-2011

Non-collinear coupling between magnetic adatoms in carbon nanotubes

The long range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a non-collinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR

Avaliação fenológica e screening fitoquímico de Mansoa alliacea (LAM.) A. Gentry - Bignoniaceae.

O trabalho teve como objetivo determinar o período de floração e frutificação do cipó d?alho cultivado no horto de plantas medicinais da Embrapa Amazônia Oriental. O estudo foi realizado no período de agosto de 2010 a maio de 2011. O cipó d?alho apresentou um período de 3 a 20 dias de floração sem ocorrer frutificação, favorecendo a coleta de folhas. O screening fitoquímico identificou a presença de oito compostos químicos naturais do metabolismo secundário da Mansoa alliacea.PIBIC-2011

Avaliação fenológica e screening fitoquímico de Averrhoa carambola L.- Oxalidaceae.

O trabalho teve como objetivo determinar o período de floração e frutificação da carambola cultivada no horto de plantas medicinais da Embrapa Amazônia Oriental. O estudo foi realizado no período de agosto de 2010 a maio de 2011. A carambola apresentou um período de 15 a 21 dias de floração e frutificação, favorecendo a coleta de folhas por mês, sendo que o mês de janeiro apresentou o maior número de dias em que a espécie floresceu e frutificou. Enquanto, o mês de dezembro foi o que apresentou o menor número (15 dias). O screening fitoquímico identificou a presença de 14 compostos químicos naturais do metabolismo secundário da Averrhoa carambola.PIBIC-2011

Scaling functions from q-deformed Virasoro characters

We propose a renormalization group scaling function which is constructed from q-deformed fermionic versions of Virasoro characters. By comparison with alternative methods, which take their starting point in the massive theories, we demonstrate that these new functions contain qualitatively the same information. We show that these functions allow for RG-flows not only amongst members of a particular series of conformal field theories, but also between different series such as N=0,1,2 supersymmetric conformal field theories. We provide a detailed analysis of how Weyl characters may be utilized in order to solve various recurrence relations emerging at the fixed points of these flows. The q-deformed Virasoro characters allow furthermore for the construction of particle spectra, which involve unstable pseudo-particles.Comment: 31 pages of Latex, 5 figure

Planck intermediate results XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck

The nearby Chamaeleon clouds have been observed in rays by the Fermi Large Area Telescope (LAT) and in thermal dust emission by Planck and IRAS. Cosmic rays and large dust grains, if smoothly mixed with gas, can jointly serve with the Hi and ^(12)CO radio data to (i) map the hydrogen column densities, NH, in the different gas phases, in particular at the dark neutral medium (DNM) transition between the Hi-bright and CO-bright media; (ii) constrain the CO-to-H_2 conversion factor, XCO; and (iii) probe the dust properties per gas nucleon in each phase and map their spatial variations across the clouds. We have separated clouds at local, intermediate, and Galactic velocities in Hi and ^(12)CO line emission to model in parallel the -ray intensity recorded between 0.4 and 100 GeV; the dust optical depth at 353 GHz, τ_(353); the thermal radiance of the large grains; and an estimate of the dust extinction, A_(VQ), empirically corrected for the starlight intensity. The dust and -ray models have been coupled to account for the DNM gas. The consistent -ray emissivity spectra recorded in the different phases confirm that the GeV–TeV cosmic rays probed by the LAT uniformly permeate all gas phases up to the ^(12)CO cores. The dust and cosmic rays both reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the Hi-DNM-CO transitions for five separate clouds. CO-dark H_2 dominates the molecular columns up to A_V ≃ 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected A_(VQ) extinction largely provides the best fit to the total gas traced by the rays. Nevertheless, we find evidence for a marked rise in A_(VQ)=N_H with increasing N_H and molecular fraction, and with decreasing dust temperature. The rise in τ_(353)=N_H is even steeper. We observe variations of lesser amplitude and orderliness for the specific power of the grains, except for a coherent decline by half in the CO cores. This combined information suggests grain evolution. We provide average values for the dust properties per gas nucleon in the different phases. The rays and dust radiance yield consistent XCO estimates near 0.7 x 10^(20) cm^(-2) K^(-1) km^(-1) s. The AVQ and τ_(353) tracers yield biased values because of the large rise in grain opacity in the CO clouds. These results clarify a recurrent disparity in the -ray versus dust calibration of X_(CO), but they confirm the factor of 2 difference found between the X_(CO) estimates in nearby clouds and in the neighbouring spiral arms