1,562 research outputs found
Extending the applicability of an open-ring trap to perform experiments with a single laser-cooled ion
An open-ring ion trap, also referred to as transparent trap was initially
built up to perform - correlation experiments with radioactive
ions. This trap geometry is also well suited to perform experiments with
laser-cooled ions, serving for the development of a new type of Penning trap,
in the framework of the project TRAPSENSOR at the University of Granada. The
goal of this project is to use a single Ca ion as detector for
single-ion mass spectrometry. Within this project and without any modification
to the initial electrode configuration, it was possible to perform Doppler
cooling on Ca ions, starting from large clouds and reaching single
ion sensitivity. This new feature of the trap might be important also for other
experiments with ions produced at Radioactive Ion Beam (RIB) facilities. In
this publication, the trap and the laser system will be described, together
with their performance with respect to laser cooling applied to large ion
clouds down to a single ion.Comment: 9 pages, 13 figure
An ultra scale-down analysis of the recovery by dead-end centrifugation of human cells for therapy.
An ultra scale-down method is described to determine the response of cells to recovery by dead-end (batch) centrifugation under commercially defined manufacturing conditions. The key variables studied are the cell suspension hold time prior to centrifugation, the relative centrifugal force (RCF), time of centrifugation, cell pellet resuspension velocities, and number of resuspension passes. The cell critical quality attributes studied are the cell membrane integrity and the presence of selected surface markers. Greater hold times and higher RCF values for longer spin times all led to the increased loss of cell membrane integrity. However, this loss was found to occur during intense cell resuspension rather than the preceding centrifugation stage. Controlled resuspension at low stress conditions below a possible critical stress point led to essentially complete cell recovery even at conditions of extreme centrifugation (e.g., RCF of 10000 g for 30 mins) and long (~2 h) holding times before centrifugation. The susceptibility to cell loss during resuspension under conditions of high stress depended on cell type and the age of cells before centrifugation and the level of matrix crosslinking within the cell pellet as determined by the presence of detachment enzymes or possibly the nature of the resuspension medium. Changes in cell surface markers were significant in some cases but to a lower extent than loss of cell membrane integrity. Biotechnol. Bioeng. 2015;112: 997-1011. © 2014 Wiley Periodicals, Inc
Metallicity of the SrTiO3 surface induced by room temperature evaporation of alumina
It is shown that a metallic state can be induced on the surface of SrTiO3
crystals by the electron beam evaporation of oxygen deficient alumina or
insulating granular aluminium. No special preparation nor heating of the SrTiO3
surface is needed. Final metallic or insulating states can be obtained
depending on the oxygen pressure during the evaporation process.
Photoconductivity and electrical field effect are also demonstrated.Comment: 8 pages, 3 figure
Screening and conductance relaxations in insulating granular aluminium thin films
We have recently found in insulating granular Al thin film a new experimental
feature (Delahaye et al., Phys. Rev. Lett. 106, 186602, 2011), namely the
existence of a conductance relaxation that is not sensitive to gate voltage
changes. This conductance relaxation is related to the existence of a
metallic-like screening in the film and can be used to estimate its
characteristic length scale. In the present paper, we give some experimental
details on how this feature was measured and present our first results on the
screening length temperature dependence.Comment: 14th Transport in interacting disordered systems (TIDS14) conference,
September 5-8 2011, Acre (Israel
Ageing and relaxation times in disordered insulators
We focus on the slow relaxations observed in the conductance of disordered
insulators at low temperature (especially granular aluminum films). They
manifest themselves as a temporal logarithmic decrease of the conductance after
a quench from high temperatures and the concomitant appearance of a field
effect anomaly centered on the gate voltage maintained. We are first interested
in ageing effects, i.e. the age dependence of the dynamical properties of the
system. We stress that the formation of a second field effect anomaly at a
different gate voltage is not a "history free" logarithmic (lnt) process, but
departs from lnt in a way which encodes the system's age. The apparent
relaxation time distribution extracted from the observed relaxations is thus
not "constant" but evolves with time. We discuss what defines the age of the
system and what external perturbation out of equilibrium does or does not
rejuvenate it. We further discuss the problem of relaxation times and comment
on the commonly used "two dip" experimental protocol aimed at extracting
"characteristic times" for the glassy systems (granular aluminum, doped indium
oxide...). We show that it is inoperable for systems like granular Al and
probably highly doped InOx where it provides a trivial value only determined by
the experimental protocol. But in cases where different values are obtained
like in lightly doped InOx or some ultra thin metal films, potentially
interesting information can be obtained, possibly about the "short time"
dynamics of the different systems. Present ideas about the effect of doping on
the glassiness of disordered insulators may also have to be reconsidered.Comment: to appear in the proceedings of the 14th International Conference on
Transport and Interactions in Disordered Systems (TIDS14
Charging of highly resistive granular metal films
We have used the Scanning Kelvin probe microscopy technique to monitor the
charging process of highly resistive granular thin films. The sample is
connected to two leads and is separated by an insulator layer from a gate
electrode. When a gate voltage is applied, charges enter from the leads and
rearrange across the sample. We find very slow processes with characteristic
charging times exponentially distributed over a wide range of values, resulting
in a logarithmic relaxation to equilibrium. After the gate voltage has been
switched off, the system again relaxes logarithmically slowly to the new
equilibrium. The results cannot be explained with diffusion models, but most of
them can be understood with a hopping percolation model, in which the
localization length is shorter than the typical site separation. The technique
is very promising for the study of slow phenomena in highly resistive systems
and will be able to estimate the conductance of these systems when direct
macroscopic measurement techniques are not sensitive enough.Comment: 8 pages, 7 figure
Measurement of the sign of the spectroscopic quadrupole moment for the 2 state in Se: no evidence for oblate shape
Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation γ rays in the highly segmented MINIBALL γ-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes
- …