14 research outputs found
Rb-85 tunable-interaction Bose-Einstein condensate machine
We describe our experimental setup for creating stable Bose-Einstein
condensates of Rb-85 with tunable interparticle interactions. We use
sympathetic cooling with Rb-87 in two stages, initially in a tight
Ioffe-Pritchard magnetic trap and subsequently in a weak, large-volume crossed
optical dipole trap, using the 155 G Feshbach resonance to manipulate the
elastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85
condensates contain 4 x 10^4 atoms with a scattering length of a=+200a_0. Our
minimalist apparatus is well-suited to experiments on dual-species and spinor
Rb condensates, and has several simplifications over the Rb-85 BEC machine at
JILA (Papp, 2007; Papp and Wieman, 2006), which we discuss at the end of this
article.Comment: 10 pages, 8 figure
Single Atom Detection With Optical Cavities
We present a thorough analysis of single atom detection using optical
cavities. The large set of parameters that influence the signal-to-noise ratio
for cavity detection is considered, with an emphasis on detunings, probe power,
cavity finesse and photon detection schemes. Real device operating restrictions
for single photon counting modules and standard photodiodes are included in our
discussion, with heterodyne detection emerging as the clearly favourable
technique, particularly for detuned detection at high power.Comment: 11 pages, 8 figures, submitted to PRA, minor changes in Secs. I and
IVD.2, and revised Fig.
Measurement of inelastic losses in a sample of ultracold Rb-85
We report on the observation and characterisation of an inelastic loss
feature in collisions between ultracold Rb-85 |F=2, m_F=-2> atoms at a magnetic
field of 220 G. Our apparatus creates ultracold Rb-85 clouds by sympathetic
cooling with a Rb-87 reservoir, and can produce pure Rb-87 condensates of 10^6
atoms by a combination of evaporative cooling in a quadrupole-Ioffe magnetic
trap and further evaporation in a weak, large-volume optical dipole trap. By
combining Rb-85 and Rb-87 atoms collected in a dual-species magneto-optical
trap and selectively evaporating the heavier isotope, we demonstrate strong
sympathetic cooling of the Rb-85 cloud, increasing its phase space density by
three orders of magnitude with no detectable loss in number. We have used
ultracold samples created in this way to observe the variation of inelastic
loss in ultracold Rb-85 as a function of magnetic field near the 155 G Feshbach
resonance. We have also measured a previously unobserved loss feature at
219.9(1) G with a width of 0.28(6) G, which we associate with a narrow Feshbach
resonance predicted by theory.Comment: 4 pages, 3 figures, content change
The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products
Orchids employing sexual deceit attract males of their pollinator species through specific volatile signals that mimic female-released sex pheromones. One of these signals proved to be 2-ethyl-5-propylcyclohexan-1,3-dione (chiloglottone1), a new natural product that was shown to be most important in the relations between orchids of the genus Chiloglottis, native to Australia, and corresponding pollinator species. Systematic investigations on the mass spectrometric fragmentation pattern of 2,5-dialkylcyclohexan-1,3-diones identified key ions providing information about the structures of the substituents at positions 2 and 5. Results enabled us to identify 2-ethyl-5-pentylcyclohexan-1,3-dione (chiloglottone2) and 2-butyl-5-methylcyclohexan-1,3-dione (chiloglottone3) as new natural products that play a decisive role in the pollination syndrome of some Chiloglottis species. During field bioassays, pure synthetic samples of chiloglottone1â3 or mixtures thereof proved to be attractive to the corresponding orchid pollinators. Because of their likely biogenesis from ubiquitous fatty acid precursors, 2,5-dialkylcyclohexan-1,3-diones may represent a hitherto overlooked, widespread class of natural products
The Energy Return on Investment for Algal Biocrude: Results for a Research Production Facility
This study is an experimental determination of the energy return on investment (EROI) for algal biocrude production at a research facility at the University of Texas at Austin (UT). During the period of this assessment, algae were grown at several cultivation scales and processed using centrifugation for harvesting, electromechanical cell lysing, and a microporous hollow fiber membrane contactor for lipid separation. The separated algal lipids represent a biocrude product that could be refined into fuel and the post-extraction biomass could be converted to methane. To determine the EROI, a second-order analysis was conducted, which includes direct and indirect energy flows, but does not include energy expenses associated with capital investments. The EROI for the production process evaluated here was significantly less than 1, however, the majority of the energy consumption resulted from non-optimized growth conditions. While the experimental results do not represent an expected typical case EROI for algal fuels, the approach and end-to-end experimental determination of the different inputs and outputs provides a useful outline of the important parameters to consider in such an analysis. The Experimental Case results are the first known experimental energy balance for an integrated algal biocrude production facility, and as such, are expected to be helpful for setting research and development priorities. In addition to the Experimental Case (based on direct measurements), three analytical cases were considered in this work: (1) a Reduced (Inputs) Case, (2) a Highly Productive Case, and (3) a Literature Model. The Reduced (Inputs) Case and the Highly Productive Case speculate the energy use for a similar system in an improved, commercial-scale production setting. The Literature Model is populated with relevant data that have previously been reported in the literature. For the Experimental Case, Reduced Case, Highly Productive Case, and Literature Model, the estimated second-order EROI was 9.2 x 10(-4), 0.074, 0.22, and 0.35, respectively. These results were dominated by growth inputs (96%, 89%, 87%, and 61% of the total energy requirement, respectively). Furthermore, the EROI was adjusted using quality factors that were calculated according to the price of each input, yielding a quality-adjusted EROI that parallels a partial financial return on investment analysis. For the Experimental Case, the Reduced Case, and the Highly Productive Case, the quality-adjusted EROI was 9.2 x 10(-5), 0.013, and 0.36, respectively