Model for the overall phase-space acceptance in a Zeeman decelerator

We present a new formalism to calculate phase-space acceptance in a Zeeman decelerator. Using parameters closely mimicking previous Zeeman deceleration experiments, this approach reveals a hitherto unconsidered velocity dependence of the phase stability which we ascribe to the finite rise and fall times of the current pulses that generate the magnetic fields inside the deceleration coils. It is shown that changing the current switch-off times as the sequence progresses, so as to maintain a constant mean acceleration per pulse, can lead to a constant phase stability and hence a beam with well-defined characteristics. We also find that the time overlap between fields of adjacent coils has an influence on the phase-space acceptance. Previous theoretical and experimental results suggested unfilled regions in phase space that influence particle transmission through the decelerator. Our model provides, for the first time, a means to directly identify the origin of these effects due to coupling between longitudinal and transverse dynamics. Since optimum phase stability is restricted to a rather small parameter range in terms of the reduced position of the synchronous particle, only a limited range of final velocities can be attained using a given number of coils. We evaluate phase stability for different Zeeman deceleration sequences, and, by comparison with numerical three-dimensional particle trajectory simulations, we demonstrate that our model provides a valuable tool to find optimum parameter sets for improved Zeeman deceleration schemes. An acceleration-deceleration scheme is shown to be a useful approach to generating beams with well-defined properties for variable-energy collision experiments. More generally, the model provides significant physical insights applicable to other types of particle decelerators with finite rise and fall time fields

International study on <i>Artemia</i>: 14. Growth and survival of <i>Artemia</i> larvae of different geographical origin in a standard culture test

For characterization of strains of the brine shrimp Artemia of different geographical origin, a standard culture test has been developed in order to compare statistically growth and survival of larvae of different strains. 25 geographical strains have been studied so far -including, for 3 strains, analyses of cysts harvested at different times. Important differences in rates of growth and survival were observed between strains but not among batches of the same strain. Best performances were noted for strains from Bahia Salinas (Puerto Rico), Buenos Aires (Argentina), Chaplin Lake (Canada), Great Salt Lake (Utah, USA), Galera Zamba and Manaure (Colombia)

International study on <i>Artemia</i> : 24. Cold storage of live <i>Artemia</i> nauplii from various geographical sources: potentials and limits in aquaculture

Freshly-hatched Artemia nauplii from various geographical sources survived storage in a refrigerator (2-4°C) at densities of 2000 per ml and above. Except for Artemia from Chaplin Lake and Buenos Aires, naupliar viability was very high even after 48 h storage, and did not decrease significantly after a 24 h post-storage transfer to 25°C. Neither the naupliar dry weight nor biochemical composition changed significantly during refrigeration for most strains tested. Comparative culture-tests with stored and freshly-hatched nauplii as food for juvenile marine mysids Mysidopsis bahia M. and larval carp Cyprinus carpio L. revealed similar production performances

International study on <i>Artemia</i> (1). XVII. Energy consumption in cysts and early larval stages of various geographical strains of <i>Artemia</i>

Variations in dry weight, caloric content and ash content during cyst hatching and early larval development have been studied for various geographical strains of Artemia. In general, decapsulated cysts contain 30 to 40 % more energy than freshly hatched nauplii; for Chaplin Lake and Buenos Aires Artemia this difference amounts to 57 %. Ash contents increase as decapsulated cysts hatch into instar I and molt into instar II-III nauplii. Over a 24 h larval developmental period individual dry weights and energy contents of the nauplii decrease with 16-34 % and 22-37 % respectively.A small but significant correlation exists between the survival rate of starved nauplii and either the energy content of instar I and instar II-III nauplii or the proportional energy consumption during metabolism from decapsulated cysts to instar II-III nauplii. The potential impact of these results on the use of Artemia in aquaculture hatcheries is discussed

International study on <i>Artemia</i> : 32. Combined effects of temperature and salinity on the survival of <i>Artemia</i> of various geographical origin

The brine shrimp inhabits geographically isolated biotopes with specific biotic and abiotic conditions. This has resulted in various geographical strains between which marked genetica, biological and chemical differentiation exists. The response of 13 different Artemia strains to the combined effect of temperature and salinity has been studied. Experimental temperatures tested ranged from 18 to 34°C and salinities from 5 to 120 promille. Except for Chaplin Lake (Canada) Artemia , all strains showed high survival over a wide range of salinities (35-110 promille). For all strains the common temperature optimum was between 20 and 25°C. Interaction between temperature and salinity was negligible or very limited. Substantial differences in tolerance were recorded in particular at the lower end of the range of experimental salinities and at the upper end of the range temperatures. Resistance to high temperature seems to be related to the genetic classification of the Artemia strains in different sibling species. Differences, however, also exist among strains from the same sibling species. Genetic adaptation to high temperature seems to take place in Artemia . The data obtained provide a first guideline for strain selection for specific aquacultural purposes

Getting a Grip on the Transverse Motion in a Zeeman Decelerator

Zeeman deceleration is an experimental technique in which inhomogeneous, time-dependent magnetic fields generated inside an array of solenoid coils are used to manipulate the velocity of a supersonic beam. A 12-stage Zeeman decelerator has been built and characterized using hydrogen atoms as a test system. The instrument has several original features including the possibility to replace each deceleration coil individually. In this article, we give a detailed description of the experimental setup, and illustrate its performance. We demonstrate that the overall acceptance in a Zeeman decelerator can be significantly increased with only minor changes to the setup itself. This is achieved by applying a rather low, anti-parallel magnetic field in one of the solenoid coils that forms a temporally varying quadrupole field, and improves particle confinement in the transverse direction. The results are reproduced by three-dimensional numerical particle trajectory simulations thus allowing for a rigorous analysis of the experimental data. The findings suggest the use of a modified coil configuration to improve transverse focusing during the deceleration process.Comment: accepted by J. Chem. Phy