727 research outputs found
Observation of Spin Flips with a Single Trapped Proton
Radio-frequency induced spin transitions of one individual proton are
observed for the first time. The spin quantum jumps are detected via the
continuous Stern-Gerlach effect, which is used in an experiment with a single
proton stored in a cryogenic Penning trap. This is an important milestone
towards a direct high-precision measurement of the magnetic moment of the
proton and a new test of the matter-antimatter symmetry in the baryon sector
Resolution of Single Spin-Flips of a Single Proton
The spin magnetic moment of a single proton in a cryogenic Penning trap was
coupled to the particle's axial motion with a superimposed magnetic bottle.
Jumps in the oscillation frequency indicate spin-flips and were identified
using a Bayesian analysis.Comment: accepted for publication by Phys. Rev. Lett., submitted 6.June.201
Investigation of acceptor levels and hole scattering mechanisms in p-gallium selenide by means of transport measurements under pressure
The effect of pressure on acceptor levels and hole scattering mechanisms in
p-GaSe is investigated through Hall effect and resistivity measurements under
quasi-hydrostatic conditions up to 4 GPa. The pressure dependence of the hole
concentration is interpreted through a carrier statistics equation with a
single (nitrogen) or double (tin) acceptor whose ionization energies decrease
under pressure due to the dielectric constant increase. The pressure effect on
the hole mobility is also accounted for by considering the pressure
dependencies of both the phonon frequencies and the hole-phonon coupling
constants involved in the scattering rates.Comment: 13 pages, Latex, 4 ps figures. to appear in High Pressure Research 69
(1997
Direct high-precision measurement of the magnetic moment of the proton
The spin-magnetic moment of the proton is a fundamental property of
this particle. So far has only been measured indirectly, analysing the
spectrum of an atomic hydrogen maser in a magnetic field. Here, we report the
direct high-precision measurement of the magnetic moment of a single proton
using the double Penning-trap technique. We drive proton-spin quantum jumps by
a magnetic radio-frequency field in a Penning trap with a homogeneous magnetic
field. The induced spin-transitions are detected in a second trap with a strong
superimposed magnetic inhomogeneity. This enables the measurement of the
spin-flip probability as a function of the drive frequency. In each measurement
the proton's cyclotron frequency is used to determine the magnetic field of the
trap. From the normalized resonance curve, we extract the particle's magnetic
moment in units of the nuclear magneton . This
measurement outperforms previous Penning trap measurements in terms of
precision by a factor of about 760. It improves the precision of the forty year
old indirect measurement, in which significant theoretical bound state
corrections were required to obtain , by a factor of 3. By application
of this method to the antiproton magnetic moment the fractional
precision of the recently reported value can be improved by a factor of at
least 1000. Combined with the present result, this will provide a stringent
test of matter/antimatter symmetry with baryons.Comment: published in Natur
Towards a high-precision measurement of the antiproton magnetic moment
The recent observation of single spins flips with a single proton in a
Penning trap opens the way to measure the proton magnetic moment with high
precision. Based on this success, which has been achieved with our apparatus at
the University of Mainz, we demonstrated recently the first application of the
so called double Penning-trap method with a single proton. This is a major step
towards a measurement of the proton magnetic moment with ppb precision. To
apply this method to a single trapped antiproton our collaboration is currently
setting up a companion experiment at the antiproton decelerator of CERN. This
effort is recognized as the Baryon Antibaryon Symmetry Experiment (BASE). A
comparison of both magnetic moment values will provide a stringent test of CPT
invariance with baryons.Comment: Submitted to LEAP 2013 conference proceeding
Coastal scenic beauty and sensitivity at the balearic islands, spain: Implication of natural and human factors
Coastal areas globally are facing a significant range of environmental stresses, enhanced by climate change-related processes and a continuous increase of human activities. The economic benefits of tourism are well-known for coastal regions, but, very often, conflicts arise between short-term benefits and long-term conservation goals. Among beach user preferences, five parameters of greater importance stand out from the rest, i.e., safety, facilities, water quality, litter and scenery; the latter is the main concern of this study. A coastal scenic evaluation was carried out in the Balearic Islands and focused on two major issues: coastal scenic beauty together with sensitivity to natural processes and human pressure. The archipelago is renowned as a top international coastal tourist destination that receives more than 13.5 million visitors (2019). Impressive landscape diversity makes the Balearics Islands an ideal field for this research. In total, 52 sites, respectively located in Ibiza (11), Formentera (5), Mallorca (18) and Menorca (18), were field-tested. In a first step, coastal scenic beauty was quantified using the coastal scenic evaluation system (CSES) method, based on the evaluation of 26 physical and human parameters, and using weighting matrices parameters and fuzzy logic mathematics. An evaluation index (“D”) was obtained for each site, allowing one to classify them in one of the five scenic classes established by the method. Twenty-nine sites were included in class I, corresponding to extremely attractive sites (CSES), which were mainly observed in Menorca. Several sound measures were proposed to maintain and/or enhance sites’ scenic value. In a second step, scenic sensitivity was evaluated using a novel methodological approach that makes possible the assessment of three different coastal scenic sensitivity indexes (CSSI), i.e., the natural sensitivity index NSI, the human sensitivity index HSI and the total sensitivity index TSI. Future climate change trends and projection of tourism development, studied at municipality scale, were considered as correction factors. All the islands showed places highly sensitive to environmental processes, while sensitivity to human pressure was essentially observed at Ibiza and Mallorca. Thereafter, sites were categorized into one of three sensitive groups established by the methodology. Results obtained are useful in pointing out very sensitive sceneries as well as limiting, preventing and/or anticipating future scenic degradation linked to natural and human issues
Demonstration of the Double Penning Trap Technique with a Single Proton
Spin flips of a single proton were driven in a Penning trap with a
homogeneous magnetic field. For the spin-state analysis the proton was
transported into a second Penning trap with a superimposed magnetic bottle, and
the continuous Stern-Gerlach effect was applied. This first demonstration of
the double Penning trap technique with a single proton suggests that the
antiproton magnetic moment measurement can potentially be improved by three
orders of magnitude or more
Tin-related double acceptors in gallium selenide single crystals
Gallium selenide single crystals doped with different amounts of tin are studied through resistivity and Hall effect measurements in the temperature range from 30 to 700 K. At low doping concentration tin is shown to behave as a double acceptor impurity in gallium selenide with ionization energies of 155 and 310 meV. At higher doping concentration tin also introduces deep donor levels, but the material remains p-type in the whole studied range of tin doping concentrations. The deep character of donors in gallium selenide is discussed by comparison of its conduction band structure to that of indium selenide under pressure. The double acceptor center is proposed to be a tin atom in interlayer position, with a local configuration that is similar to that of tin diselenide. The hole mobility exhibits an anomalous dependence on the tin content, attaining its maximum value in the ingot with 0.2% nominal tin content. This is proposed to be related to impurity pairing effects giving rise to thermal shallow acceptors with low ionization energy and low carrier scattering cross section, making the hole mobility to be controlled by phonon scattering mechanisms even for relatively high impurity [email protected] ; [email protected]
Identification and validation of copy number variants using SNP genotyping arrays from a large clinical cohort.
BACKGROUND: Genotypes obtained with commercial SNP arrays have been extensively used in many large case-control or population-based cohorts for SNP-based genome-wide association studies for a multitude of traits. Yet, these genotypes capture only a small fraction of the variance of the studied traits. Genomic structural variants (GSV) such as Copy Number Variation (CNV) may account for part of the missing heritability, but their comprehensive detection requires either next-generation arrays or sequencing. Sophisticated algorithms that infer CNVs by combining the intensities from SNP-probes for the two alleles can already be used to extract a partial view of such GSV from existing data sets.
RESULTS: Here we present several advances to facilitate the latter approach. First, we introduce a novel CNV detection method based on a Gaussian Mixture Model. Second, we propose a new algorithm, PCA merge, for combining copy-number profiles from many individuals into consensus regions. We applied both our new methods as well as existing ones to data from 5612 individuals from the CoLaus study who were genotyped on Affymetrix 500K arrays. We developed a number of procedures in order to evaluate the performance of the different methods. This includes comparison with previously published CNVs as well as using a replication sample of 239 individuals, genotyped with Illumina 550K arrays. We also established a new evaluation procedure that employs the fact that related individuals are expected to share their CNVs more frequently than randomly selected individuals. The ability to detect both rare and common CNVs provides a valuable resource that will facilitate association studies exploring potential phenotypic associations with CNVs.
CONCLUSION: Our new methodologies for CNV detection and their evaluation will help in extracting additional information from the large amount of SNP-genotyping data on various cohorts and use this to explore structural variants and their impact on complex traits
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