Linking Ultracold Polar Molecules

We predict that pairs of polar molecules can be weakly bound together in an ultracold environment, provided that a dc electric field is present. The field that links the molecules together also strongly influences the basic properties of the resulting dimer, such as its binding energy and predissociation lifetime. Because of their long-range character these dimers will be useful in disentangling cold collision dynamics of polar molecules. As an example, we estimate the microwave photoassociation yield for OH-OH cold collisions.Comment: 4 pages 2 figure

Ouantitative anatomy in 3 cultivare of Dichanthium aristatum (Poiret) C. E. Hubbard (Poaceae) to infer its forage valué

Ha sido bien demostrada la influencia de los componentes anatómicos sobre la digestibílidad de las gramíneas forrajeras. Por ello, se estudia la anatomía cuantitativa foliar y caulinar de tres cultivares de Dichanthium aristatum, rastrero, el formoseño y col. 821. Las plantas fueron cultivadas en el campo experimental de la Estación Experimental Agropecuaria INTA Reconquista, Provincia de Santa Fe, Argentina. Para determinar las diferencias anatómicas se realizaron cortes transversales de hoja y tallo, calculándose el área de cada tejido con un planímetro digital electrónico, expresándose los resultados como porcentaje del total de la sección transversal. Los parámetros analizados fueron los distintos tejidos foliares y caulinares, el número de haces vasculares y el peso específico foliar. Además, se calculó el porcentaje de TLND (tejidos lentamente y no digestibles). En los cultivares bajo estudio se encontraron diferencias significativas en el porcentaje de esclerénquima y parénquima. El peso específico foliar y el número de haces vasculares fue mayor en el cv et formoseño. Se halló una relación positiva entre TLND y los tejidos de paredes engrosadas, y negativa entre el TLND y los tejidos parénquima incoloro y clorénquima.The influence of anatomic components on digestibility has been already demostrated in forage grasses. For this purpose the quantftative anatomy of leaf and stem of three cv of Dichanthium aristatum, rastrero, e¡ formoseño and col. 821) ha ve been studied. Plants were cultívated in the expefimentahfiefd of EEA ANTA Reconquista, Santa FeProvince, Argentino. To determine anatomic diferences standard transverse sections of leaves and stems were made and the area of each tissue was obtained by means of an electronic digital planimeter, expressing the resutts as percentage of the whole cross section. The parameters studied were the difFerents leaf and stem tissues, the number of vascular bundles and the speciftc leaf weight. The percentage occupied by SNDT (slowly and no digestibles tissues) was calculated. The resulte were evaluated with the variance methods, and the means compared by the Scheffe Test. In the cultivare under study significant differences in the sclerenchyma and parenchyma percentage were observad. The specific leaf weight and the number of vascular bundles were greater in cv el formoseño. A {positivo relation between SNDT and thick-walled tissues, and an inverse irelation between SNDT and colorless iparenchyma and chlorenchyma were observed.Universidad Nacional de La Plata (UNLP) - Facultad de Ciencias Agrarias y Forestale

Ouantitative anatomy in 3 cultivare of Dichanthium aristatum (Poiret) C. E. Hubbard (Poaceae) to infer its forage valué

Ha sido bien demostrada la influencia de los componentes anatómicos sobre la digestibílidad de las gramíneas forrajeras. Por ello, se estudia la anatomía cuantitativa foliar y caulinar de tres cultivares de Dichanthium aristatum, rastrero, el formoseño y col. 821. Las plantas fueron cultivadas en el campo experimental de la Estación Experimental Agropecuaria INTA Reconquista, Provincia de Santa Fe, Argentina. Para determinar las diferencias anatómicas se realizaron cortes transversales de hoja y tallo, calculándose el área de cada tejido con un planímetro digital electrónico, expresándose los resultados como porcentaje del total de la sección transversal. Los parámetros analizados fueron los distintos tejidos foliares y caulinares, el número de haces vasculares y el peso específico foliar. Además, se calculó el porcentaje de TLND (tejidos lentamente y no digestibles). En los cultivares bajo estudio se encontraron diferencias significativas en el porcentaje de esclerénquima y parénquima. El peso específico foliar y el número de haces vasculares fue mayor en el cv et formoseño. Se halló una relación positiva entre TLND y los tejidos de paredes engrosadas, y negativa entre el TLND y los tejidos parénquima incoloro y clorénquima.The influence of anatomic components on digestibility has been already demostrated in forage grasses. For this purpose the quantftative anatomy of leaf and stem of three cv of Dichanthium aristatum, rastrero, e¡ formoseño and col. 821) ha ve been studied. Plants were cultívated in the expefimentahfiefd of EEA ANTA Reconquista, Santa FeProvince, Argentino. To determine anatomic diferences standard transverse sections of leaves and stems were made and the area of each tissue was obtained by means of an electronic digital planimeter, expressing the resutts as percentage of the whole cross section. The parameters studied were the difFerents leaf and stem tissues, the number of vascular bundles and the speciftc leaf weight. The percentage occupied by SNDT (slowly and no digestibles tissues) was calculated. The resulte were evaluated with the variance methods, and the means compared by the Scheffe Test. In the cultivare under study significant differences in the sclerenchyma and parenchyma percentage were observad. The specific leaf weight and the number of vascular bundles were greater in cv el formoseño. A {positivo relation between SNDT and thick-walled tissues, and an inverse irelation between SNDT and colorless iparenchyma and chlorenchyma were observed.Universidad Nacional de La Plata (UNLP) - Facultad de Ciencias Agrarias y Forestale

Formation of Pairing Fields in Resonantly Coupled Atomic and Molecular Bose-Einstein Condensates

In this paper, we show that pair-correlations may play an important role in the quantum statistical properties of a Bose-Einstein condensed gas composed of an atomic field resonantly coupled with a corresponding field of molecular dimers. Specifically, pair-correlations in this system can dramatically modify the coherent and incoherent transfer between the atomic and molecular fields.Comment: 4 pages, 4 figure

Bright filter-free source of indistinguishable photon pairs

We demonstrate a high-brightness source of pairs of indistinguishable photons based on a type-II phase-matched doubly-resonant optical parametric oscillator operated far below threshold. The cavity-enhanced down-conversion output of a PPKTP crystal is coupled into two single-mode fibers with a mode coupling efficiency of 58%. The high degree of indistinguishability between the photons of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher than 90% without any filtering at an instantaneous coincidence rate of 450 000 pairs/s per mW of pump power per nm of down-conversion bandwidth. For the degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70 pairs/(s mW MHz) is estimated, increasing the spectral brightness for indistinguishable photons by two orders of magnitude compared to similar previous sources.Comment: 7 pages, 3 figure

Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate

The process of stimulated Raman adiabatic passage (STIRAP) provides a possible route for the generation of a coherent molecular Bose-Einstein condensate (BEC) from an atomic BEC. We analyze this process in a three-dimensional mean-field theory, including atom-atom interactions and non-resonant intermediate levels. We find that the process is feasible, but at larger Rabi frequencies than anticipated from a crude single-mode lossless analysis, due to two-photon dephasing caused by the atomic interactions. We then identify optimal strategies in STIRAP allowing one to maintain high conversion efficiencies with smaller Rabi frequencies and under experimentally less demanding conditions.Comment: Final published versio

Theoretical model for ultracold molecule formation via adaptive feedback control

We investigate pump-dump photoassociation of ultracold molecules with amplitude- and phase-modulated femtosecond laser pulses. For this purpose a perturbative model for the light-matter interaction is developed and combined with a genetic algorithm for adaptive feedback control of the laser pulse shapes. The model is applied to the formation of 85Rb2 molecules in a magneto-optical trap. We find for optimized pulse shapes an improvement for the formation of ground state molecules by more than a factor of 10 compared to unshaped pulses at the same pump-dump delay time, and by 40% compared to unshaped pulses at the respective optimal pump-dump delay time. Since our model yields directly the spectral amplitudes and phases of the optimized pulses, the results are directly applicable in pulse shaping experiments

Curved Tails in Polymerization-Based Bacterial Motility

The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a visually striking signature of actin polymerization-based motility. Similar actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae, the Vaccinia virus, and vesicles and microspheres in related in vitro systems. We show that the torque required to produce the curvature in the tail can arise from randomly placed actin filaments pushing the bacterium or particle. We find that the curvature magnitude determines the number of actively pushing filaments, independent of viscosity and of the molecular details of force generation. The variation of the curvature with time can be used to infer the dynamics of actin filaments at the bacterial surface.Comment: 8 pages, 2 figures, Latex2

Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates

We study the photodissociation chemistry of a quantum degenerate gas of bosonic triatomic $ABC$ molecules, assuming two open rearrangement channels ($AB+C$ or $A+BC$). The equations of motion are equivalent to those of a parametric multimode laser, resulting in an exponential buildup of macroscopic mode populations. By exponentially amplifying a small differential in the single-particle rate-coefficients, Bose stimulation leads to a nearly complete selectivity of the collective $N$-body process, indicating a novel type of ultra-selective quantum degenerate chemistry.Comment: 5 pages, 3 figure