Resolved-sideband laser cooling in a penning trap

We report the laser cooling of a single $^{40}\text{Ca}^+$ ion in a Penning trap to the motional ground state in one dimension. Cooling is performed in the strong binding limit on the 729-nm electric quadrupole $S_{1/2}\leftrightarrow D_{5/2}$ transition, broadened by a quench laser coupling the $D_{5/2}$ and $P_{3/2}$ levels. We find the final ground state occupation to be $98\pm1\%$. We measure the heating rate of the trap to be very low with $\dot{\bar{n}}\approx 0.3\pm0.2\textrm{s}^{-1}$ for trap frequencies from $150-400\textrm{kHz}$, consistent with the large ion-electrode distance.Comment: 4 pages, 6 figures. Accepted: Phys. Rev. Lett. (2016) http://journals.aps.org/prl/accepted/b6074YefH1115b5881f77975417a6ae0bc9f652a

Antibody-resistant mutants of Borrelia burgdorferi: in vitro selection and characterization.

We used polyclonal antisera and monoclonal antibodies (mAbs) to inhibit the growth of clonal populations of two strains of Borrelia burgdorferi, the Lyme disease agent, and thereby select for antibody-resistant mutants. mAbs were directed at the outer membrane proteins, OspA or OspB. Mutants resistant to the growth-inhibiting properties of the antibodies were present in the populations at frequencies ranging from 10(-5) to 10(-2). The several escape variants that were examined were of four classes. Class I mutants were resistant to all mAbs; they lacked OspA and OspB and the linear plasmid that encodes them. Two other proteins were expressed in larger amounts in class I mutants; mAbs to these proteins inhibited the mutant but not the wild-type cells. Class II mutants were resistant to some but not all mAbs; they had truncated OspA and/or OspB proteins. Class III mutants were resistant only to the selecting mAb; they had full-length Osp proteins that were not bound by the selecting antibody in Western blots. In two class III mutants resistant to different anti-OspA mAbs, missense mutations were demonstrated in the ospA genes. Class IV mutants were likewise resistant only to selecting antibody, but in this case the selecting antibody still bound in Western blots

Digital preservation at Big Data scales: proposing a step-change in preservation system architectures

Purpose The purpose of this paper is to consider how digital preservation system architectures will support business analysis of large-scale collections of preserved resources, and the use of Big Data analyses by future researchers. Design/methodology/approach This paper reviews the architecture of existing systems, then discusses experimental surveys of large digital collections using existing digital preservation tools at Big Data scales. Finally, it introduces the design of a proposed new architecture to work with Big Data volumes of preserved digital resources – also based upon experience of managing a collection of 30 million digital images. Findings Modern visualisation tools enable business analyses based on file-related metadata, but most currently available systems need more of this functionality “out-of-the-box”. Scalability of preservation architecture to Big Data volumes depends upon the ability to run preservation processes in parallel, so indexes that enable effective sub-division of collections are vital. Not all processes scale easily: those that do not require complex management. Practical implications The complexities caused by scaling up to Big Data volumes can be seen as being at odds with preservation, where simplicity matters. However, the sustainability of preservation systems relates directly to their usefulness, and maintaining usefulness will increasingly depend upon being able to process digital resources at Big Data volumes. An effective balance between these conflicting situations must be struck. Originality/value Preservation systems are at a step-change as they move to Big Data scale architectures and respond to more technical research processes. This paper is a timely illustration of the state of play at this pivotal moment. The Polonsky Foundatio

Pattern Onset ERGs and VEPs Produced by Patterns Arising From Light Increment and Decrement

PURPOSE: Our aim was to elaborate how on and off signals contribute to pattern ERGs and pattern visual evoked potentials (VEPs) by using pedestal patterns arising from incremental and decremental onset stimulation. METHODS: Pattern onset/offset ERGs and VEPs were produced by black and white checks of 60' side length and 88% spatial contrast appearing in a 16° field for 200 ms from white (110 cd/m2), black (7 cd/m2), and gray (48 cd/m2) backgrounds and disappeared for 1000 ms. Twenty healthy subjects participated in the study (median age 19.5, range, 5-31 years), 10 of whom also underwent pattern onset/offset ERG recordings to the same stimuli (median age 25.7, range, 22-31 years). VEPs were recorded from an occipital array referred to Fz. Pattern electroretinograms (PERGs) were recorded from "Dawson-Trick-Litzkow" (DTL) plus corneal electrodes referred to ipsilateral outer canthi. RESULTS: There was high correlation within subjects of the VEP waveform produced by patterns arising from light increment and decrement (group mean correlation coefficient of PVEPs to check appearance from black versus white: 87%). An average of increment and decrement PERGs simulated the onset PERG from a gray background. This waveform is akin to standard International Society for Clinical Electrophysiology of Vision (ISCEV) clinical PERGs to reversing checks. CONCLUSIONS: In healthy individuals, the early components of the pattern onset/offset VEP waveforms are comparable to light increment and decrement pedestal stimulation. Pattern onset/offset ERGs to pedestal stimulation may be used to probe simultaneous recording of ERGs with VEPs in order to obtain an assessment of retinal ganglion cell and optic pathway function in patients with less stable fixation

Experiences of graduating students from a medical programme five years after curricular transformation: A descriptive study

Background. The University of the Witwatersrand introduced a new curriculum in 2003 where students could gain admission to the medicalprogramme at two levels: directly as school leavers or following a degree as graduate entrants at the third year of study. From this point both groups of students continue in a combined class in a single curriculum.Objective. To determine the experiences of the fifth cohort of graduating students from a medical programme following curricular transformation.Method. A quantitative descriptive study was undertaken using a semi-structured questionnaire with both open- and closed-ended questions. There were 201 students in the graduating class, all of whom were invited to complete the questionnaire.Results. A 74% response rate was obtained, of which 66% were school leaver entrants and 34% were graduates. Among the best experiences there were 59 comments relating directly to the programme. The worst experiences included perceptions of the lack of standardisation in clinical exams and feelings of inadequacy in relation to pharmacology and microbiology. Just under three-quarters of the participants felt ‘adequately prepared’ for the clinical years; 82% of the participants stated that they would make changes to the programme.Conclusion. The placement of this evaluation at the conclusion of formal assessments may have contributed to the depth of responses and openness of respondents in the completion of the questionnaire. We highly recommend the value of obtaining data on students’ experiences and opinions of a programme at the point of exit from the programme

Uptake, distribution and elimination of palladium-doped polystyrene nanoplastics in rainbow trout (Oncorhynchus mykiss) following dietary exposure.

The ingestion of nanoplastics (NPs) by fish has led to concerns regarding fish health and food chain transfer, but analytical constraints have hindered quantitative data collection on their uptake and depuration. We used palladium-doped polystyrene nanoplastics (PS-Pd NPs, ~200 nm) to track particle fate in rainbow trout (Oncorhynchus mykiss) during a week-long dietary exposure and subsequent 7-day depuration period on a control diet (no added PS-Pd NPs). At Day 3 and 7 of the exposure, and after depuration, the mid intestine, hind intestine, liver, gallbladder, kidney, gill and carcass were sampled. All organs and the carcass were analysed for total Pd content by inductively couple plasma mass spectrometry. After 3 days of exposure, the mid (32.5 ± 8.3 ng g-1) and hind (42.3 ± 8.2 ng g-1) intestine had significantly higher total Pd concentrations compared to the liver and carcass (1.3 ± 0.4 and 3.4 ± 1.1 ng g-1, respectively). At Day 7, there was no time-related difference in any organ (or the carcass) total Pd concentrations compared to Day 3. When the total Pd content was expressed as a body distribution based on mass of tissue, the carcass contained the highest fraction with 72.5 ± 5.2 % at Day 7, which could raise concerns over transfer to higher trophic levels. The total number of particles that entered the fish over the 7 days was 94.5 ± 13.5 × 106 particles, representing 0.07 ± 0.01 % of the Pd the fish had been fed. Following depuration, there was no detectable Pd in any organ or the carcass, indicating clearance from the fish. These data indicate that these NPs are taken into the internal organs and carcass of fish, yet removal of the exposure results in substantial excretion to below the limit of detection

Novel designs for Penning ion traps

Project supported by the European Commission within the FP5 RTD programmes HITRAP and QGATES and the Integrated Project FET/QIPC “SCALA” FP6. We also acknowledge the support from the EPSRC. JRCP acknowledges the support by CONACyT, SEP and the ORS Awards

Plans for laser spectroscopy of trapped cold hydrogen-like HCI

Laser spectroscopy studies are being prepared to measure the 1s ground state hyperfine splitting in trapped cold highly charged ions. The purpose of such experiments is to test quantum electrodynamics in the strong electric field regime. These experiments form part of the HITRAP project at GSI. A brief review of the planned experiments is presented.Comment: 4 pages, 4 figures, accepted for publication (NIMB

Control of the conformations of ion Coulomb crystals in a Penning trap

Laser-cooled atomic ions form ordered structures in radiofrequency ion traps and in Penning traps. Here we demonstrate in a Penning trap the creation and manipulation of a wide variety of ion Coulomb crystals formed from small numbers of ions. The configuration can be changed from a linear string, through intermediate geometries, to a planar structure. The transition from a linear string to a zigzag geometry is observed for the first time in a Penning trap. The conformations of the crystals are set by the applied trap potential and the laser parameters, and agree with simulations. These simulations indicate that the rotation frequency of a small crystal is mainly determined by the laser parameters, independent of the number of ions and the axial confinement strength. This system has potential applications for quantum simulation, quantum information processing and tests of fundamental physics models from quantum field theory to cosmology