5,020 research outputs found
Strongly aligned and oriented molecular samples at a kHz repetition rate
We demonstrate strong adiabatic laser alignment and mixed-field orientation
at kHz repetition rates. We observe degrees of alignment as large as
cos\Theta=0.94 at 1 kHz operation for iodobenzene. The experimental setup
consist of a kHz laser system simultaneously producing pulses of 30 fs (1.3 mJ)
and 450 ps (9 mJ). A cold 1 K state-selected molecular beam is produced at the
same rate by appropriate operation of an Even-Lavie valve. Quantum state
selection has been obtained using an electrostatic deflector. A camera and data
acquisition system records and analyzes the images on a single-shot basis. The
system is capable of producing, controlling (translation and rotation) and
analyzing cold molecular beams at kHz repetition rates and is, therefore,
ideally suited for the recording of ultrafast dynamics in so-called "molecular
movies".Comment: 6 pages, 4 figures, in press in Mol. Phys., accepted in February
2013, in final production (galley proofs done) since March 8, 2013, v3 only
adds publication dat
Two-state wave packet for strong field-free molecular orientation
We demonstrate strong laser-field-free orientation of absolute-ground-state
carbonyl sulfide molecules. The molecules are oriented by the combination of a
485-ps-long non-resonant laser pulse and a weak static electric field. The
edges of the laser pulse create a coherent superposition of two rotational
states resulting in revivals of strong transient molecular orientation after
the laser pulse. The experimentally attained degree of orientation of 0.6
corresponds to the theoretical maximum for mixing of the two states. Switching
off the dc field would provide the same orientation completely field-free
Determination of mean atmospheric densities from the explorer ix satellite
Mean atmospheric densities from changes in orbital elements of Explorer IX satellit
Profile scaling in decay of nanostructures
The flattening of a crystal cone below its roughening transition is studied
by means of a step flow model. Numerical and analytical analyses show that the
height profile, h(r,t), obeys the scaling scenario dh/dr = F(r t^{-1/4}). The
scaling function is flat at radii r<R(t) \sim t^{1/4}. We find a one parameter
family of solutions for the scaling function, and propose a selection criterion
for the unique solution the system reaches.Comment: 4 pages, RevTex, 3 eps figure
Strongly driven quantum pendulum of the OCS molecule
We demonstrate and analyze a strongly driven quantum pendulum in the angular
motion of stateselected and laser aligned OCS molecules. Raman-couplings during
the rising edge of a 50-picosecond laser pulse create a wave packet of pendular
states, which propagates in the confining potential formed by the
polarizability interaction between the molecule and the laser field. This
wave-packet dynamics manifests itself as pronounced oscillations in the degree
of alignment with a laser-intensity dependent period.Comment: 6 pages, 4 figure
Atlantic Herring and Horse Mackerel in 6aS/7b; Industry Acoustic Survey Cruise Report
An acoustic survey of Atlantic herring Clupea harengus and horse mackerel Trachurus trachurus was conducted in ICES areas 6aS/7b in Nov 2018 using the pair trawl vessels MFV Eilean Croine S238 and MFV Sparkling Star D437. This survey is the third in a time series that is hoped will be developed into a long-term index of spawning/pre-spawning herring and horse mackerel in 6aS/7b, for use in stock assessments in the future. The survey design was based on the predicted distribution of herring and horse mackerel in this area during this time. In total 1,400nmi of cruise track was completed using 37 transects and related to a total area coverage of approximately 5,600 nmiÂČ. Parallel transect spacing was set at 7.5nmi for the wider area strata, and 3.5nmi for Donegal Bay and Achill strata. Coverage extended from inshore coastal areas to the 200 m contour in the west and north where possible. A survey was carried out in Lough Swilly using a zig-zag design. A Simrad ES-38B (38 kHz) split-beam transducer mounted on a towed body was used to collect acoustic raw data. Very strong herring marks were evident in Lough Swilly, an area where boats in the monitoring fishery were concentrating effort. There were a few herring marks in discreet areas around Glen Head, Bruckless Bay, Inishmurray and Inishbofin. A total of four commercial fishing hauls on horse mackerel were completed during the survey. Biological samples from the monitoring fishery of herring were used to augment the samples from the survey. Herring samples were taken from boats fishing in Lough Swilly and Bruckless Bay as close spatially and temporally as possible to the survey in these areas. Herring were dominated overall by 4-wr fish, 29% of the overall numbers. Horse mackerel were distributed throughout the survey area, but particularly throughout the area to the north and west of the Stags of Broadhaven. Horse mackerel length distribution was dominated by a mode at 25-26cm. This corresponded to a dominance of 4-wr fish (~89%) in all of the samples. The total stock biomass (TSB) estimate of herring for the combined 6aS/7b area was 50,145 tonnes (Lough Swilly = 32,372 tonnes, Donegal Bay = 9,517 tonnes, NW area = 7,710 tonnes and the remaining Achill strata = 545 tonnes). This is considered to be a minimum estimate of herring in the 6aS/7b survey area at the time of the survey. The TSB estimate of horse mackerel for the total surveyed area in 6aS/7b area was 57,162 tonnes, considered to be a minimum estimate of horse mackerel in the 6aS/7b survey area at the time of the survey. The CV estimates on biomass and abundance are high (~0.51 for herring and ~ 0.36 for horse mackerel) for the survey in 2018. For herring, this is mostly caused by the over-reliance on a few acoustic marks of herring in Lough Swilly and Bruckless Bay in particular. Horse mackerel are a widely distributed stock, therefore the stock was not contained by this survey
Step Bunching with Alternation of Structural Parameters
By taking account of the alternation of structural parameters, we study
bunching of impermeable steps induced by drift of adatoms on a vicinal face of
Si(001). With the alternation of diffusion coefficient, the step bunching
occurs irrespective of the direction of the drift if the step distance is
large. Like the bunching of permeable steps, the type of large terraces is
determined by the drift direction. With step-down drift, step bunches grows
faster than those with step-up drift. The ratio of the growth rates is larger
than the ratio of the diffusion coefficients. Evaporation of adatoms, which
does not cause the step bunching, decreases the difference. If only the
alternation of kinetic coefficient is taken into account, the step bunching
occurs with step-down drift. In an early stage, the initial fluctuation of the
step distance determines the type of large terraces, but in a late stage, the
type of large terraces is opposite to the case of alternating diffusion
coefficient.Comment: 8pages, 16 figure
Crossover Scaling of Wavelength Selection in Directional Solidification of Binary Alloys
We simulate dendritic growth in directional solidification in dilute binary
alloys using a phase-field model solved with an adaptive-mesh refinement. The
spacing of primary branches is examined for a range of thermal gradients and
alloy compositions and is found to undergo a maximum as a function of pulling
velocity, in agreement with experimental observations. We demonstrate that
wavelength selection is unambiguously described by a non-trivial crossover
scaling function from the emergence of cellular growth to the onset of
dendritic fingers, a result validated using published experimental data.Comment: 4 pages, four figures, submitted to Physical Review Letter
Petrogenesis of diachronous mixed siliciclastic-carbonate megafacies in the cool-water Oligocene Tikorangi Formation, Taranaki Basin, New Zealand
The Oligocene (Whaingaroan-Waitakian) Tikorangi Formation is a totally subsurface, lithostratigraphically complex, mixed siliciclastic-limestone-rich sequence forming an important fracture reservoir within Taranaki Basin, New Zealand. Petrographically the formation comprises a spectrum of interbedded rock types ranging from calcareous mudstone to wackestone to packstone to clean sparry grainstone. Skeletal and textural varieties within these rock types have aided in the identification of three environmentally distinctive megafacies for the Tikorangi Formation rocks-shelfal, foredeep, and basinal. Data from these megafacies have been used to detail previous conclusions on the petrogenesis and to further refine depositional paleoenvironmental models for the Tikorangi Formation in the central eastern Taranaki Basin margin.Shelfal Megafacies 1 rocks (reference well Hu Road-1A) are latest Oligocene (early Waitakian) in age and formed on or proximal to the Patea-Tongaporutu-Herangi basement high. They are characterised by coarse, skeletal-rich, pure sparry grainstone comprising shallow water, high energy taxa (bryozoans, barnacles, red algae) and admixtures of coarse well-rounded lithic sand derived from Mesozoic basement greywacke. This facies type has previously gone unrecorded in the Tikorangi Formation. Megafacies 2 is a latest Oligocene (early Waitakian) foredeep megafacies (formerly named shelfal facies) formed immediately basinward and west of the shelfal basement platform. It accumulated relatively rapidly (>20 cm/ka) from redeposition of shelfal megafacies biota that became intermixed with bathyal taxa to produce a spectrum of typically mudstone through to sparry grainstone. The resulting skeletal mix (bivalve, echinoderm, planktic and benthic foraminiferal, red algal, bryozoan, nannofossil) is unlike that in any of the age-equivalent limestone units in neighbouring onland King Country Basin. Megafacies 3 is an Oligocene (Whaingaroan-Waitakian) offshore basinal megafacies (formerly termed bathyal facies) of planktic foraminiferal-nannofossil-siliciclastic wackestone and mudstone formed away from redepositional influences. The siliciclastic input in this distal basinal setting (sedimentation rates <7 mm/ka) was probably sourced mainly from oceanic currents carrying suspended sediment from South Island provenances exposed at this time.Tikorangi Formation rocks record the Taranaki Basinâs only period of carbonate-dominated sedimentation across a full range of shelfal, foredeep, and basinal settings. Depositional controls on the three contrasting megafacies were fundamentally the interplay of an evolving and complex plate tectonic setting, including development of a carbonate foredeep, changes in relative sea level within an overall transgressive regime, and changing availability, sources, and modes of deposition of both bioclastic and siliciclastic sediments. The mixed siliciclastic-carbonate nature of the formation, and its skeletal assemblages, low-Mg calcite mineralogy, and delayed deep burial diagenetic history, are features consistent with formation in temperate-latitude cool waters
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