675 research outputs found
2-(4-Ferrocenylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
In the title compound,, [Fe(C5H5)(C17H20BO2)], the two near parallel cyclopentadienyl rings of the ferrocene group are eclipsed. The benzene ring is tilted with respect to the attached cyclopentadiene ring by 17.0 (1)° and by 24.2 (1)° with respect to the dioxaborolane ring. The molecules assemble in the crystal via C—H⋯π interactions between the cyclopentadienyl H atoms and the benzene and cyclopentadienyl rings of neighbouring molecules
Ethyl 4-hydroxymethyl-2-methylpyridine-5-carboxylate
The title compound, C10H13NO3, was obtained as a by-product of the aldolization reaction of furo[3,4-c]pyridin-3(1H)-one with thiophene-2-carboxaldehyde. The substituents on the pyridine ring are nearly coplanar, with an 8.1 (2)° rotation of the hydroxmethyl group from this plane. The molecules assemble in the crystal structure as chains via O—H⋯N hydrogen bonding between the pyridine N atom and a neighbouring hydroxymethyl OH group
Transport of ultracold Bose gases beyond the Gross-Pitaevskii description
We explore atom-laser-like transport processes of ultracold Bose-condensed
atomic vapors in mesoscopic waveguide structures beyond the Gross-Pitaevskii
mean-field theory. Based on a microscopic description of the transport process
in the presence of a coherent source which models the outcoupling from a
reservoir of perfectly Bose-Einstein condensed atoms, we derive a system of
coupled quantum evolution equations that describe the dynamics of a dilute
condensed Bose gas in the framework of the Hartree-Fock-Bogoliubov
approximation. We apply this method to study the transport of dilute Bose gases
through an atomic quantum dot and through waveguides with disorder. Our
numerical simulations reveal that the onset of an explictly time-dependent flow
corresponds to the appearance of strong depletion of the condensate on the
microscopic level and leads to a loss of global phase coherence.Comment: 12 pages, 7 figure
Bis(N,N-diethyldithiocarbamato)(1,10-phenanthroline)cobalt(III) tetrafluoridoborate
The cationic complex in the structure of the title compound, [Co(Et2NCS2)2(C12H8N2)]BF4, has a CoIII atom with a distorted octahedral coordination formed by four S atoms of two diethyldithiocarbamate and two N atoms of 1,10-phenanthroline ligands. The crystal structure features head-to-tail stacking of the phenanthroline ligands. The tetrafluoridoborate anions are positioned in the channels between the cation stacks running along the a axis, and form weak C—H⋯F interactions
Tailoring optical nonlinearities via the Purcell effect
We predict that the effective nonlinear optical susceptibility can be
tailored using the Purcell effect. While this is a general physical principle
that applies to a wide variety of nonlinearities, we specifically investigate
the Kerr nonlinearity. We show theoretically that using the Purcell effect for
frequencies close to an atomic resonance can substantially influence the
resultant Kerr nonlinearity for light of all (even highly detuned) frequencies.
For example, in realistic physical systems, enhancement of the Kerr coefficient
by one to two orders of magnitude could be achieved
Control of Phytoplankton Growth by Iron and Silicic Acid Availability in the Subantarctic Ocean: Experimental Results From the SAZ Project
Subantarctic Southern Ocean surface waters in the austral summer and autumn are characterized by high concentrations of nitrate and phosphate but low concentrations of dissolved iron (Fe, similar to0.05 nM) and silicic acid (Si, \u3c1 muM). During the Subantarctic Zone AU9706 cruise in March 1998 we investigated the relative importance of Fe and Si in controlling phytoplankton growth and species composition at a station within the subantarctic water mass (46.8degreesS, 142degreesE) using shipboard bottle incubation experiments. Treatments included unamended controls; 1.9 nM added iron (+Fe); 9 muM added silicic acid (+Si); and 1.9 nM addediron plus 9 muM added silicic acid (+Fe+Si). We followed a detailed set of biological and biogeochemical parameters over 8 days. Fe added alone clearly increased community growth rates and nitrate drawdown and altered algal community composition relative to control treatments. Surprisingly, small, lightly silicified pennate diatoms grew when Fe was added either with or without Si, despite the extremely low ambient silicic acid concentrations. Pigment analyses suggest that lightly silicified chrysophytes (type 4 haptophytes) may have preferentially responded to Si added either with or without Fe. However, for many of the parameters measured the +Fe+Si treatments showed large increases relative to both the +Fe and +Si treatments. Our results suggest that iron is the proximate limiting nutrient for chlorophyll production, photosynthetic efficiency, nitrate drawdown, and diatom growth, but that Si also exerts considerable control over algal growth and species composition. Both nutrients together are needed to elicit a maximum growth response, suggesting that both Fe and Si play important roles in structuring the subantarctic phytoplankton community
Control of Phytoplankton Growth by Iron Supply and Irradiance in the Subantarctic Southern Ocean: Experimental Results From the SAZ Project
The influence of irradiance and Fe supply on phytoplankton processes was studied, north (47°S, 142°E) and south (54°S, 142°E) of the Subantarctic Front in austral autumn (March 1998). At both sites, resident cells exhibited nutrient stress (Fv/Fm 0 at 47°S and 9% I0 at 54°S because of MLDs of 40 (47°S) and 90 m (54°S), when these stations were occupied. The greater MLD at 54°S is reflected by tenfold higher cellular chlorophyll a levels in the resident phytoplankton. In the 47°S experiment, chlorophyll a levels increased to \u3e1 μg/L-1 only in the high-Fe treatments, regardless of irradiance levels, suggesting Fe limitation. This trend was also noted for cell abundances, silica production, and carbon fixation rates. In contrast, in the 54°S experiment there were increases in chlorophyll a (to \u3e2 μg/L-1), cell abundances, silica production, and carbon fixation only in the high-light treatments to which Fe had been added, suggesting that Fe and irradiance limit algal growth rates. Irradiance by altering algal Fe quotas is a key determinant of algal growth rate at 54°S (when silicic acid levels are nonlimiting); however, because of the integral nature of Fe/light colimitation and the restricted nature of the current data set, it was not possible to ascertain the relative contributions of Fe and irradiance to the control of phytoplankton growth. On the basis of a climatology of summer mean MLD for subantarctic (SA) waters south of Australia the 47° and 54°S sites appear to represent minimum and maximum MLDs, where Fe and Fe/irradiance, respectively, may limit/colimit algal growth. The implications for changes in the factors limiting algal growth with season in SA waters are discussed
(±)-Cyclohexane-1,2-diyl bis(4-nitrobenzoate)
The crystal structure of the title compound, C20H18N2O8, has been investigated to establish the relative stereochemistry between the ester groups. The cyclohexane ring adopts a chair conformation, in which the two ester groups occupy the adjacent equatorial positions in a trans relationship with each other. The molecules assemble in the crystal as chains along the c axis via C—H⋯π interactions between the cyclohexane ring and a pair of nitrophenyl rings of the neighbouring molecule. Also observed are π–π stacking interactions between the nitrophenyl rings of neighbouring chains, with a perpendicular distance between these rings of 3.409 Å and a slippage of 0.969 Å
(1R,6R,13R,18R)-(Z,Z)-1,18-Bis[(4R)-2,2-dimethyl-1,3-dioxolan-4-yl]-3,16-dimethylene-8,20-diazadispiro[5.6.5.6]tetracosa-7,19-diene
The crystal structure of the title compound, C34H54N2O4, has been solved in order to prove the relative and absolute chirality of the newly-formed stereocentres which were established using an asymmetric Diels–Alder reaction at an earlier stage in the synthesis. This unprecedented stable dialdimine contains a 14-membered ring and was obtained as the minor diastereoisomer in the Diels–Alder reaction. The absolute stereochemistry of the stereocentres of the acetal functionality was known to be R based on the use of a chiral (R)-trisubstituted dienophile derived from enantiopure (S)-glyceraldehyde. The assignment of the configuration in the dienophile and the title di-aldimine differs from (S)-glyceraldehyde due to a change in the priority order of the substituents. The crystal structure establishes the presence of six stereocentres all attributed to be R. The 14-membered ring contains two aldimine bonds [C—N = 1.258 (2) and 1.259 (2) Å]. It adopts a similar conformation to that proposed for trans–trans-cyclotetradeca-1,8-dienes
(±)-2′-Phenylcyclohexanespiro-4′-(azepano[1,2-b]isoxazolidine)
In the crystal structure of the racemic title isoxazolidine, C19H27NO, the relative stereochemistry between the phenyl group and the bridgehead H atom is shown to be syn. There are two molecules in the asymmetric unit, one of which is the 7R*,13R* enantiomer, and one of which is the 7S*,13S* enantiomer. These enantiomers adopt different orientations of the phenyl ring with respect to the isoxazolidine ring, with C—C—C—C torsion angles of 63.6 (4) and 86.8 (4)°, respectively. In both enantiomers, the six-membered ring adopts a chair conformation, while the seven-membered ring adopts a twist-chair conformation
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