1,507 research outputs found
A nanofabricated, monolithic, path-separated electron interferometer
We report a self-aligned, monolithic electron interferometer, consisting of
two 45 nm thick silicon layers separated by 20 m. This interferometer was
fabricated from a single crystal silicon cantilever on a transmission electron
microscope grid by gallium focused ion-beam milling. Using this interferometer,
we demonstrate beam path-separation, and obtain interference fringes in a
Mach-Zehnder geometry, in an unmodified 200 kV transmission electron
microscope. The fringes have a period of 0.32 nm, which corresponds to the
lattice planes of silicon, and a maximum
contrast of 15 %. This design can potentially be scaled to millimeter-scale,
and used in electron holography. It can also be applied to perform fundamental
physics experiments, such as interaction-free measurement with electrons.Comment: 21 pages (including supplementary info), 8 figures; Corrected typos,
added references for introduction and conclusion, changed ordering of
paragraphs of Discussion, results unchange
Clinical surveillance of thrombotic microangiopathies in Scotland, 2003-2005
The prevalence, incidence and outcomes of haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are not well established in adults or children from prospective studies. We sought to identify both outcomes and current management strategies using prospective, national surveillance of HUS and TTP, from 2003 to 2005 inclusive. We also investigated the links between these disorders and factors implicated in the aetiology of HUS and TTP including infections, chemotherapy, and immunosuppression. Most cases of HUS were caused by verocytotoxin-producing Escherichia coli (VTEC), of which serotype O157 predominated, although other serotypes were identified. The list of predisposing factors for TTP was more varied although use of immunosuppressive agents and severe sepsis, were the most frequent precipitants. The study demonstrates that while differentiating between HUS and TTP is sometimes difficult, in most cases the two syndromes have quite different predisposing factors and clinical parameters, enabling clinical and epidemiological profiling for these disorders
Penning traps as a versatile tool for precise experiments in fundamental physics
This review article describes the trapping of charged particles. The main
principles of electromagnetic confinement of various species from elementary
particles to heavy atoms are briefly described. The preparation and
manipulation with trapped single particles, as well as methods of frequency
measurements, providing unprecedented precision, are discussed. Unique
applications of Penning traps in fundamental physics are presented.
Ultra-precise trap-measurements of masses and magnetic moments of elementary
particles (electrons, positrons, protons and antiprotons) confirm
CPT-conservation, and allow accurate determination of the fine-structure
constant alpha and other fundamental constants. This together with the
information on the unitarity of the quark-mixing matrix, derived from the
trap-measurements of atomic masses, serves for assessment of the Standard Model
of the physics world. Direct mass measurements of nuclides targeted to some
advanced problems of astrophysics and nuclear physics are also presented
Shell-model description of monopole shift in neutron-rich Cu
Variations in the nuclear mean-field, in neutron-rich nuclei, are
investigated within the framework of the nuclear shell model. The change is
identified to originate mainly from the monopole part of the effective two-body
proton-neutron interaction. Applications for the low-lying states in odd- Cu
nuclei are presented. We compare the results using both schematic and realistic
forces. We also compare the monopole shifts with the results obtained from
large-scale shell-model calculations, using the same realistic interaction, in
order to study two-body correlations beyond the proton mean-field variations.Comment: Phys. Rev. C (in press
Silicon in foods: content and bioavailability
The silicon content of various foodstuffs marketed in Belgium was measured by a validated graphite furnace absorption spectrometric method. Dietary intake has been identified as the major source of silicon. However, data on its bioavailability remain scarce and insufficient. In vitro methods can provide an indication of bioavailability in case of lacking in vivo data. Bioavailability of silicon from different foodstuffs was estimated using an in vitro continuous flow gastroduodenal simulation method. The major food sources of silicon were unrefined grains, cereal products and root vegetables. The availabilities of silicon from, meat, milk and beers were high, whereas low availability was observed for seafood and cereal products. Plotting the availability data versus the total elemental silicon content of the foods revealed an exponential inverse relationship. The inverse relationship between silicon content and silicon availability was found in all foods, with the exception of various silicon containing drinks. Nevertheless, food categories classified as major silicon sources in the diet still appear to provide the highest absolute amounts of available silicon per 100 g of food including breakfast cereals, bread and baking products, and beers
CPT and Lorentz Tests in Penning Traps
A theoretical analysis is performed of Penning-trap experiments testing CPT
and Lorentz symmetry through measurements of anomalous magnetic moments and
charge-to-mass ratios. Possible CPT and Lorentz violations arising from
spontaneous symmetry breaking at a fundamental level are treated in the context
of a general extension of the SU(3) x SU(2) x U(1) standard model and its
restriction to quantum electrodynamics. We describe signals that might appear
in principle, introduce suitable figures of merit, and estimate CPT and Lorentz
bounds attainable in present and future Penning-trap experiments. Experiments
measuring anomaly frequencies are found to provide the sharpest tests of CPT
symmetry. Bounds are attainable of approximately in the
electron-positron case and of for a suggested experiment with
protons and antiprotons. Searches for diurnal frequency variations in these
experiments could also limit certain types of Lorentz violation to the level of
in the electron-positron system and others at the level of
in the proton-antiproton system. In contrast, measurements comparing
cyclotron frequencies are sensitive within the present theoretical framework to
different kinds of Lorentz violation that preserve CPT. Constraints could be
obtained on one figure of merit in the electron-positron system at the level of
, on another in the proton-antiproton system at , and on a
third at using comparisons of ions with antiprotons.Comment: 31 pages, published in Physical Review
Silicon in foods: content and bioavailability
The silicon content of various foodstuffs marketed in Belgium was measured by a validated graphite furnace absorption spectrometric method. Dietary intake has been identified as the major source of silicon. However, data on its bioavailability remain scarce and insufficient. In vitro methods can provide an indication of bioavailability in case of lacking in vivo data. Bioavailability of silicon from different foodstuffs was estimated using an in vitro continuous flow gastroduodenal simulation method. The major food sources of silicon were unrefined grains, cereal products and root vegetables. The availabilities of silicon from, meat, milk and beers were high, whereas low availability was observed for seafood and cereal products. Plotting the availability data versus the total elemental silicon content of the foods revealed an exponential inverse relationship. The inverse relationship between silicon content and silicon availability was found in all foods, with the exception of various silicon containing drinks. Nevertheless, food categories classified as major silicon sources in the diet still appear to provide the highest absolute amounts of available silicon per 100 g of food including breakfast cereals, bread and baking products, and beers
Magnetic field stabilization for high-accuracy mass measurements on exotic nuclides
The magnetic-field stability of a mass spectrometer plays a crucial role in
precision mass measurements. In the case of mass determination of short-lived
nuclides with a Penning trap, major causes of instabilities are temperature
fluctuations in the vicinity of the trap and pressure fluctuations in the
liquid helium cryostat of the superconducting magnet. Thus systems for the
temperature and pressure stabilization of the Penning trap mass spectrometer
ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the
fluctuations by at least one order of magnitude downto dT=+/-5mK and
dp=+/-50mtorr has been achieved, which corresponds to a relative frequency
change of 2.7x10^{-9} and 1.5x10^{-10}, respectively. With this stabilization
the frequency determination with the Penning trap only shows a linear temporal
drift over several hours on the 10 ppb level due to the finite resistance of
the superconducting magnet coils.Comment: 23 pages, 13 figure
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
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