Bragg spectroscopy of a superfluid Bose-Hubbard gas

Bragg spectroscopy is used to measure excitations of a trapped, quantum-degenerate gas of 87Rb atoms in a 3-dimensional optical lattice. The measurements are carried out over a range of optical lattice depths in the superfluid phase of the Bose-Hubbard model. For fixed wavevector, the resonant frequency of the excitation is found to decrease with increasing lattice depth. A numerical calculation of the resonant frequencies based on Bogoliubov theory shows a less steep rate of decrease than the measurements.Comment: 11 pages, 4 figure

Multi-channel scattering and Feshbach resonances: Effective theory, phenomenology, and many-body effects

A low energy effective theory based on a microscopic multi-channel description of the atom-atom interaction is derived for the scattering of alkali atoms in different hyperfine states. This theory describes all scattering properties, including medium effects, in terms of the singlet and triplet scattering lengths and the range of the atom-atom potential and provides a link between a microscopic description of Feshbach scattering and more phenomenological approaches. It permits the calculation of medium effects on the resonance coming from the occupation of closed channel states. The examination of such effects are demonstrated to be of particular relevance to an experimentally important Feshbach resonance for $^{40}$K atoms. We analyze a recent rethermalization rate experiment on $^{40}$K and demonstrate that a measurement of the temperature dependence of this rate can determine the magnetic moment of the Feshbach molecule. Finally, the energy dependence of the Feshbach interaction is shown to introduce a negative effective range inversely proportional to the width of the resonance. Since our theory is based on a microscopic multi-channel picture, it allows the explicit calculation of corrections to commonly used approximations such as the neglect of the effective range and the treatment of the Feshbach molecule as a point boson.Comment: 10 pages, 5 figures. Typos corrected. Accepted for PR

Determination of the s-wave Scattering Length of Chromium

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes $^{52}$Cr and $^{50}$Cr. From the time constants for cross-dimensional thermalization in atomic samples we have determined the magnitudes $|a(^{52}Cr)|=(170 \pm 39)a_0$ and $|a(^{50}Cr)|=(40 \pm 15)a_0$, where $a_0=0.053nm$. By measuring the rethermalization rate of $^{52}$Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and single-channel calculations, we have obtained strong evidence that the sign of $a(^{52}Cr)$ is positive. Rescaling our $^{52}$Cr model potential to $^{50}$Cr strongly suggests that $a(^{50}Cr)$ is positive, too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and

Cavity induced modifications to the resonance fluorescence and probe absorption of a laser-dressed V atom

A cavity-modified master equation is derived for a coherently driven, V-type three-level atom coupled to a single-mode cavity in the bad cavity limit. We show that population inversion in both the bare and dressed-state bases may be achieved, originating from the enhancement of the atom-cavity interaction when the cavity is resonant with an atomic dressed-state transition. The atomic populations in the dressed state representation are analysed in terms of the cavity-modified transition rates. The atomic fluorescence spectrum and probe absorption spectrum also investigated, and it is found that the spectral profiles may be controlled by adjusting the cavity frequency. Peak suppression and line narrowing occur under appropriate conditions.Comment: 12 pages, 10 postscript figures, to be appeared in Phys. Rev.

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

Antibody-mediated immunity to the obligate intracellular bacterial pathogen Coxiella burnetii is Fc receptor- and complement-independent

<p>Abstract</p> <p>Background</p> <p>The obligate intracellular bacterial pathogen <it>Coxiella burnetii </it>causes the zoonosis Q fever. The intracellular niche of <it>C. burnetii </it>has led to the assumption that cell-mediated immunity is the most important immune component for protection against this pathogen. However, passive immunization with immune serum can protect naïve animals from challenge with virulent <it>C. burnetii</it>, indicating a role for antibody (Ab) in protection. The mechanism of this Ab-mediated protection is unknown. Therefore, we conducted a study to determine whether Fc receptors (FcR) or complement contribute to Ab-mediated immunity (AMI) to <it>C. burnetii</it>.</p> <p>Results</p> <p>Virulent <it>C. burnetii </it>infects and replicates within human dendritic cells (DC) without inducing their maturation or activation. We investigated the effects of Ab opsonized <it>C. burnetii </it>on human monocyte-derived and murine bone marrow-derived DC. Infection of DC with Ab-opsonized <it>C. burnetii </it>resulted in increased expression of maturation markers and inflammatory cytokine production. Bacteria that had been incubated with naïve serum had minimal effect on DC, similar to virulent <it>C. burnetii </it>alone. The effect of Ab opsonized <it>C. burnetii </it>on DC was FcR dependent as evidenced by a reduced response of DC from FcR knockout (FcR k/o) compared to C57Bl/6 (B6) mice. To address the potential role of FcR in Ab-mediated protection in vivo, we compared the response of passively immunized FcR k/o mice to the B6 controls. Interestingly, we found that FcR are not essential for AMI to <it>C. burnetii </it>in vivo. We subsequently examined the role of complement in AMI by passively immunizing and challenging several different strains of complement-deficient mice and found that AMI to <it>C. burnetii </it>is also complement-independent.</p> <p>Conclusion</p> <p>Despite our data showing FcR-dependent stimulation of DC in vitro, Ab-mediated immunity to <it>C. burnetii </it>in vivo is FcR-independent. We also found that passive immunity to this pathogen is independent of complement.</p

Suppression of power-broadening in strong-coupling photoassociation in the presence of a Feshbach resonance

Photoassociation (PA) spectrum in the presence of a magnetic Feshbach resonance is analyzed. Nonperturbative solution of the problem yields analytical expressions for PA linewidth and shift which are applicable for arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance. We show that by tuning magnetic field close to Fano minimum, it is possible to suppress power broadening at increased laser intensities. This occurs due to quantum interference of PA transitions from unperturbed and perturbed continuum. Line narrowing at high laser intensities is accompanied by large spectral shifts. We briefly discuss important consequences of line narrowing in cold collisions.Comment: 12 pages, 5 figure

Autler-Townes splitting in two-color photoassociation of 6Li

We report on high-resolution two-color photoassociation spectroscopy in the triplet system of magneto-optically trapped 6Li. The absolute transition frequencies have been measured. Strong optical coupling of the bound molecular states has been observed as Autler-Townes splitting in the photoassociation signal. The spontaneous bound-bound transition rate is determined and the molecule formation rate is estimated. The observed lineshapes are in good agreement with the theoretical model.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A (Rapid Communication