1,467 research outputs found
Uniaxial pressure dependence of magnetic order in MnSi
We report comprehensive small angle neutron scattering (SANS) measurements
complemented by ac susceptibility data of the helical order, conical phase and
skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all
crystallographic orientations uniaxial pressure favours the phase for which a
spatial modulation of the magnetization is closest to the pressure axis.
Uniaxial pressures as low as 1kbar applied perpendicular to the magnetic field
axis enhance the skyrmion lattice phase substantially, whereas the skyrmion
lattice phase is suppressed for pressure parallel to the field. Taken together
we present quantitative microscopic information how strain couples to magnetic
order in the chiral magnet MnSi.Comment: 23 pages, includes supplemen
A cross-linguistic database of phonetic transcription systems
Contrary to what non-practitioners might expect, the systems of phonetic notation used by linguists are highly idiosyncratic. Not only do various linguistic subfields disagree on the specific symbols they use to denote the speech sounds of languages, but also in large databases of sound inventories considerable variation can be found. Inspired by recent efforts to link cross-linguistic data with help of reference catalogues (Glottolog, Concepticon) across different resources, we present initial efforts to link different phonetic notation systems to a catalogue of speech sounds. This is achieved with the help of a database accompanied by a software framework that uses a limited but easily extendable set of non-binary feature values to allow for quick and convenient registration of different transcription systems, while at the same time linking to additional datasets with restricted inventories. Linking different transcription systems enables us to conveniently translate between different phonetic transcription systems, while linking sounds to databases allows users quick access to various kinds of metadata, including feature values, statistics on phoneme inventories, and information on prosody and sound classes. In order to prove the feasibility of this enterprise, we supplement an initial version of our cross-linguistic database of phonetic transcription systems (CLTS), which currently registers five transcription systems and links to fifteen datasets, as well as a web application, which permits users to conveniently test the power of the automatic translation across transcription systems
Mapping deuterated methanol toward L1544: I. Deuterium fraction and comparison with modeling
The study of deuteration in pre-stellar cores is important to understand the
physical and chemical initial conditions in the process of star formation. In
particular, observations toward pre-stellar cores of methanol and deuterated
methanol, solely formed on the surface of dust grains, may provide useful
insights on surface processes at low temperatures. Here we analyze maps of CO,
methanol, formaldehyde and their deuterated isotopologues toward a well-known
pre-stellar core. This study allows us to test current gas-dust chemical
models. Single-dish observations of CHOH, CHDOH, HCO,
H_2\,^{13}CO, HDCO, DCO and CO toward the prototypical pre-stellar
core L1544 were performed at the IRAM 30 m telescope. We analyze their column
densities, distributions, and compare these observations with gas-grain
chemical models. The maximum deuterium fraction derived for methanol is
[CHDOH]/[CHOH] 0.080.02, while the measured deuterium
fractions of formaldehyde at the dust peak are [HDCO]/[HCO]
0.030.02, [DCO]/[HCO] 0.040.03 and [DCO]/[HDCO]
1.20.3. Observations differ significantly from the predictions of
models, finding discrepancies between a factor of 10 and a factor of 100 in
most cases. It is clear though that to efficiently produce methanol on the
surface of dust grains, quantum tunneling diffusion of H atoms must be switched
on. It also appears that the currently adopted reactive desorption efficiency
of methanol is overestimated and/or that abstraction reactions play an
important role. More laboratory work is needed to shed light on the chemistry
of methanol, an important precursor of complex organic molecules in space.Comment: Accepted for publication in A&
Versatile module for experiments with focussing neutron guides
We report the development of a versatile module that permits fast and
reliable use of focussing neutron guides under varying scattering angles. A
simple procedure for setting up the module and neutron guides is illustrated by
typical intensity patterns to highlight operational aspects as well as typical
parasitic artefacts. Combining a high-precision alignment table with separate
housings for the neutron guides on kinematic mounts, the change-over between
neutron guides with different focussing characteristics requires no
readjustments of the experimental set-up. Exploiting substantial gain factors,
we demonstrate the performance of this versatile neutron scattering module in a
study of the effects of uniaxial stress on the domain populations in the
transverse spin density wave phase of single crystal Cr
LAGOVirtual: A Collaborative Environment for the Large Aperture GRB Observatory
We present the LAGOVirtual Project: an ongoing project to develop platform to
collaborate in the Large Aperture GRB Observatory (LAGO). This continental-wide
observatory is devised to detect high energy (around 100 GeV) component of
Gamma Ray Bursts, by using the single particle technique in arrays of Water
Cherenkov Detectors (WCD) at high mountain sites (Chacaltaya, Bolivia, 5300 m
a.s.l., Pico Espejo, Venezuela, 4750 m a.s.l., Sierra Negra, Mexico, 4650 m
a.s.l). This platform will allow LAGO collaboration to share data, and computer
resources through its different sites. This environment has the possibility to
generate synthetic data by simulating the showers through AIRES application and
to store/preserve distributed data files collected by the WCD at the LAGO
sites. The present article concerns the implementation of a prototype of
LAGO-DR adapting DSpace, with a hierarchical structure (i.e. country,
institution, followed by collections that contain the metadata and data files),
for the captured/simulated data. This structure was generated by using the
community, sub-community, collection, item model; available at the DSpace
software. Each member institution-country of the project has the appropriate
permissions on the system to publish information (descriptive metadata and
associated data files). The platform can also associate multiple files to each
item of data (data from the instruments, graphics, postprocessed-data, etc.).Comment: Second EELA-2 Conference Choroni, Venezuela, November 25th to 27th
200
Reciprocal space mapping of magnetic order in thick epitaxial MnSi films
We report grazing incidence small angle neutron scattering (GISANS) and
complementary off-specular neutron reflectometry (OSR) of the magnetic order in
a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit.
Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a
magnetic modulation perpendicular to the films under magnetic fields parallel
and perpendicular to the film, where additional polarized neutron reflectometry
(PNR) and magnetization measurements are in excellent agreement with the
literature. Regardless of field orientation, our data does not suggest the
presence of more complex spin textures, notably the formation of skyrmions.
This observation establishes a distinct difference with bulk samples of MnSi of
similar thickness under perpendicular field, in which a skyrmion lattice
dominates the phase diagram. Extended x-ray absorption fine structure
measurements suggest that small shifts of the Si positions within the
unstrained unit cell control the magnetic state, representing the main
difference between the films and thin bulk samples
Opportunistic dose amplification for proton and carbon ion therapy via capture of internally generated thermal neutrons
© 2018, The Author(s). This paper presents Neutron Capture Enhanced Particle Therapy (NCEPT), a method for enhancing the radiation dose delivered to a tumour relative to surrounding healthy tissues during proton and carbon ion therapy by capturing thermal neutrons produced inside the treatment volume during irradiation. NCEPT utilises extant and in-development boron-10 and gadolinium-157-based drugs from the related field of neutron capture therapy. Using Monte Carlo simulations, we demonstrate that a typical proton or carbon ion therapy treatment plan generates an approximately uniform thermal neutron field within the target volume, centred around the beam path. The tissue concentrations of neutron capture agents required to obtain an arbitrary 10% increase in biological effective dose are estimated for realistic treatment plans, and compared to concentrations previously reported in the literature. We conclude that the proposed method is theoretically feasible, and can provide a worthwhile improvement in the dose delivered to the tumour relative to healthy tissue with readily achievable concentrations of neutron capture enhancement drugs
New results for the missing quantum numbers labeling the quadrupole and octupole boson basis
The many -pole boson states, with ,
realize the irreducible representation (IR) for the group reduction chains
. They have been analytically
studied and widely used for the description of nuclear systems. However, no
analytical expression for the degeneracy of the 's IR,
determined by the reduction , is available. Thus, the
number of distinct values taken by has been so far obtained by
solving some complex equations. Here we derive analytical expressions for the
degeneracy characterizing the octupole and quadrupole boson states,
respectively. The merit of this work consists of the fact that it completes the
analytical expressions for the -pole boson basis.Comment: 10page
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