Creating long-lived neutral-atom traps in a cryogenic environment

We describe techniques for creating long-lived magneto-optical and magnetostatic traps for neutral atoms. These traps exist in a sealed cryogenic environment with a temperature near 4 K, where the background gas pressure can be extremely low. To date we have observed cesium magneto-optical traps with background-limited lifetimes in excess of 1 h, and magnetostatic traps with lifetimes of nearly 10 min. From these observations we use the known He-Cs van der Waals collision cross section to infer typical background gas pressures in our apparatus below 4×10^(-12) Torr. With hardware improvements we expect this pressure can be made much lower, extending the magnetostatic-trap lifetimes one to two orders of magnitude. Furthermore, with a cryogenic system one can use superconducting magnets and SQUID detectors to trap and to nondestructively sense spin-polarized atoms. With superconducting microstructures one can achieve very large magnetic-field gradients and curvatures, as high as ∼10^6 G/cm and ∼10^9 G/cm^2, respectively, for use in magnetic and magneto-optical traps

Stability of Magneto-optical Traps with Large Field Gradients: Limits on the Tight Confinement of Single Atoms

We report measurements of the stability of magneto-optical traps (MOTs) for neutral atoms in the limit of tight confinement of a single atom. For quadrupole magnetic field gradients at the trap center greater than ∼1 kG/cm, we find that stochastic diffusion of atoms out of the trapping volume becomes the dominant particle loss mechanism, ultimately limiting the MOT size to greater than ∼5 μm. We measured and modeled the diffusive loss rate as a function of laser power, detuning, and field gradient for trapped cesium atoms. In addition, for as few as two atoms, the collisional loss rates become very high for tightly confined traps, allowing the direct observation of isolated two-body atomic collisions in a MOT

<i>Laophontopsis</i> Sars and the taxonomic concept of the Normanellinae (Copepoda: Harpacticoida): a revision

The taxonomic concept of the subfamily Normanellinae Lang (Harpacticoida, Laophontidae) is revised. As a result a new family Laophontopsidae is proposed to accommodate Laophontopsis Sars and two new genera Aculeopsis and Telodocus. It is concluded that the presumed boreo-mediterranean distribution pattern displayed by the type species L. lamellifera (Claus) is merely the result of erroneous identifications. The population of northwest Europe is assigned to a new species L. borealis and another new species L. monardi is proposed for Monard's (1928) material from Banyuls-sur-Mer. L. secundus Sewell is placed in the new genus Telodocus. Aculeopsis gen. nov. embraces only A. longisetosa spec. nov. and constitutes the most primitive genus of the family. The Laophontopsidae are placed within the superfamily Laophontoidea. The Normanellinae are provisionally upgraded to family level despite their diphyletic status because this narrows the diagnosis of the Laophontidae considerably. The genera are attributed to two clearly defined but non-related subfamilies, Normanellinae Lang (Normanella Brady) and Cletopsyllinae subfam. nov. (Cletopsyllus Willey, Pseudocletopsyllus Vervoort). The genus Pseudocleta Lang is relegated to incertae sedis within the Laophontoidae

Ultrasonic Attenuation Measurement Using Backscattering Technique

Ultrasonic backscattering measurements by means of spatial averaging technique were carried out in steel to determine the ultrasonic attenuation coefficient. The attenuation coefficients were evaluated from the exponential decay of the backscattering signal. The results were compared with those obtained by evaluating the amplitude decay of the main pulse. Good agreement is observed provided the condition α s · λ \u3c\u3c 1 is valid, i.e. Rayleigh scattering with d/λ ≤ 0.2 and/or weak elastic anisotropy of the single crystal. Otherwise multiple scattering becomes dominant and the amplitude decay of the backscattering curve is no longer related to the attenuation coefficient

Stability-normalised walking speed: A new approach for human gait perturbation research

© 2019 In gait stability research, neither self-selected walking speeds, nor the same prescribed walking speed for all participants, guarantee equivalent gait stability among participants. Furthermore, these options may differentially affect the response to different gait perturbations, which is problematic when comparing groups with different capacities. We present a method for decreasing inter-individual differences in gait stability by adjusting walking speed to equivalent margins of stability (MoS). Eighteen healthy adults walked on a split-belt treadmill for two-minute bouts at 0.4 m/s up to 1.8 m/s in 0.2 m/s intervals. The stability-normalised walking speed (MoS = 0.05 m) was calculated using the mean MoS at touchdown of the final 10 steps of each speed. Participants then walked for three minutes at this speed and were subsequently exposed to a treadmill belt acceleration perturbation. A further 12 healthy adults were exposed to the same perturbation while walking at 1.3 m/s: the average of the previous group. Large ranges in MoS were observed during the prescribed speeds (6–10 cm across speeds) and walking speed significantly (P < 0.001) affected MoS. The stability-normalised walking speeds resulted in MoS equal or very close to the desired 0.05 m and reduced between-participant variability in MoS. The second group of participants walking at 1.3 m/s had greater inter-individual variation in MoS during both unperturbed and perturbed walking compared to 12 sex, height and leg length-matched participants from the stability-normalised walking speed group. The current method decreases inter-individual differences in gait stability which may benefit gait perturbation and stability research, in particular studies on populations with different locomotor capacities. [Preprint: https://doi.org/10.1101/314757

Regional geothermal aquifer architecture of the fluvial Lower Cretaceous Nieuwerkerk Formation – a palynological analysis

The primary challenge for efficient geothermal doublet design and deployment is the adequate prediction of the size, shape, lateral extent and thickness (or aquifer architecture) of aquifers. In the West Netherlands Basin, fluvial Lower Cretaceous sandstone-rich successions form the main aquifers for geothermal heat exploitation. Large variations in the thickness of these successions are recognised in currently active doublet systems that cannot be explained. This creates an uncertainty in aquifer thickness prediction, which increases the uncertainty in doublet lifetime prediction as it has an impact on net aquifer volume. The goal of this study was to improve our understanding of the thickness variations and regional aquifer architecture of the Nieuwerkerk Formation geothermal aquifers. For this purpose, new palynological data were evaluated to correlate aquifers in currently active doublet systems based on their chronostratigraphic position and regional Maximum Flooding Surfaces. Based on the palynological cuttings analysis, the fluvial interval of the Nieuwerkerk Formation was subdivided into two successions: a Late Ryazanian to Early Valanginian succession and a Valanginian succession. Within these successions trends were identified in sandstone content. In combination with seismic interpretation, maps were constructed that predict aquifer thickness and their lateral extent in the basin. The study emphasises the value of palynological analyses to reduce the uncertainty of fluvial hot sedimentary aquifer exploitation