1,866 research outputs found
Automatic Spatial Calibration of Ultra-Low-Field MRI for High-Accuracy Hybrid MEG--MRI
With a hybrid MEG--MRI device that uses the same sensors for both modalities,
the co-registration of MRI and MEG data can be replaced by an automatic
calibration step. Based on the highly accurate signal model of ultra-low-field
(ULF) MRI, we introduce a calibration method that eliminates the error sources
of traditional co-registration. The signal model includes complex sensitivity
profiles of the superconducting pickup coils. In ULF MRI, the profiles are
independent of the sample and therefore well-defined. In the most basic form,
the spatial information of the profiles, captured in parallel ULF-MR
acquisitions, is used to find the exact coordinate transformation required. We
assessed our calibration method by simulations assuming a helmet-shaped
pickup-coil-array geometry. Using a carefully constructed objective function
and sufficient approximations, even with low-SNR images, sub-voxel and
sub-millimeter calibration accuracy was achieved. After the calibration,
distortion-free MRI and high spatial accuracy for MEG source localization can
be achieved. For an accurate sensor-array geometry, the co-registration and
associated errors are eliminated, and the positional error can be reduced to a
negligible level.Comment: 11 pages, 8 figures. This work is part of the BREAKBEN project and
has received funding from the European Union's Horizon 2020 research and
innovation programme under grant agreement No 68686
No Effect of Steady Rotation on Solid He in a Torsional Oscillator
We have measured the response of a torsional oscillator containing
polycrystalline hcp solid He to applied steady rotation in an attempt to
verify the observations of several other groups that were initially interpreted
as evidence for macroscopic quantum effects. The geometry of the cell was that
of a simple annulus, with a fill line of relatively narrow diameter in the
centre of the torsion rod. Varying the angular velocity of rotation up to
2\,rad\,s showed that there were no step-like features in the resonant
frequency or dissipation of the oscillator and no history dependence, even
though we achieved the sensitivity required to detect the various effects seen
in earlier experiments on other rotating cryostats. All small changes during
rotation were consistent with those occurring with an empty cell. We thus
observed no effects on the samples of solid He attributable to steady
rotation.Comment: 8 pages, 3 figures, accepted in J. Low Temp. Phy
Positron states at vacancy-impurity pairs in semiconductors
Positron states at pure monovacancies and divacancies and vacancy-phosphorus pairs in Si as well as at As vacancies and As-vacancyâAs-antisite pairs in GaAs are calculated. The dependence of the positron lifetime on the lattice relaxation around the defects is studied, and the effects related to the screening of positrons are discussed. The calculations are based on superimposing free atoms. The ability of the method to describe positron states at charged defects is demonstrated.Peer reviewe
Composite repetition-aware data structures
In highly repetitive strings, like collections of genomes from the same
species, distinct measures of repetition all grow sublinearly in the length of
the text, and indexes targeted to such strings typically depend only on one of
these measures. We describe two data structures whose size depends on multiple
measures of repetition at once, and that provide competitive tradeoffs between
the time for counting and reporting all the exact occurrences of a pattern, and
the space taken by the structure. The key component of our constructions is the
run-length encoded BWT (RLBWT), which takes space proportional to the number of
BWT runs: rather than augmenting RLBWT with suffix array samples, we combine it
with data structures from LZ77 indexes, which take space proportional to the
number of LZ77 factors, and with the compact directed acyclic word graph
(CDAWG), which takes space proportional to the number of extensions of maximal
repeats. The combination of CDAWG and RLBWT enables also a new representation
of the suffix tree, whose size depends again on the number of extensions of
maximal repeats, and that is powerful enough to support matching statistics and
constant-space traversal.Comment: (the name of the third co-author was inadvertently omitted from
previous version
Design of an electrical floor heating panel manufactured by transfer foil technology
Abstract. In this thesis, a heater-integrated floor material and its possibilities in the field of floor heating were examined. The heater was designed to be manufactured by transfer foil technology. LTSpice and COMSOL simulation tools were utilized to model power losses and heating power, and three different heater versions were designed with Altium designer, and their simulation results and other properties of the heaters were compared. The main goal of the work was to find out the possibility of making floor heating for large surface areas from these heating panels and it was found that it would be possible to make over 100mÂČ surfaces with under 1 ÂșC tolerance for the desired heating temperature.Siirtokalvotekniikalla valmistettavan sĂ€hköisen lattialĂ€mmityspaneelin suunnittelu. TiivistelmĂ€. TĂ€ssĂ€ työssĂ€ tarkasteltiin siirtokalvotekniikalla valmistettavan lĂ€mmitysvastuksen integroimista lattiamateriaaliin ja sen mahdollisuuksia lattialĂ€mmityksen saralla. TyössĂ€ hyödynnettiin LTSpice- ja COMSOL-simulointityökaluja lĂ€mmitystehon ja tehohĂ€viöiden mallinnukseen ja piirrettiin Altiumilla kolme eri lĂ€mmitinversiota ja vertailtiin niiden simulointituloksia sekĂ€ lĂ€mmittimien muita ominaisuuksia. Työn tĂ€rkeimpĂ€nĂ€ tavoitteena oli selvittÀÀ mahdollisuutta tehdĂ€ lĂ€mmityspaneeleista lattialĂ€mmitys suurille lattiapinta-aloille. Saatiin selville, ettĂ€ nĂ€illĂ€ lĂ€mmityspaneeleilla olisi mahdollista tehdĂ€ yli 100mÂČ lattiapintoja alle yhden asteen toleranssilla halutulle lĂ€mpötilalle
Blurred Responsibilities of Disaster Governance: The American Red Cross in the US and Haiti
The influence of private actors, such as non-profit organizations (NPOs) and firms, has been increasing in disaster governance. Previous literature has interrogated the responsibilities of states towards citizens in disasters, but the roles of private actors have been insufficiently challenged. The article politicizes the entangled relations between NPOs, states, and disaster-affected people. It proposes the Rawlsian division of moral labor as a useful, normative framework for interrogating the justice of disaster governance arrangements in which âliberalâ states are involved. Liberal states have two types of responsibilities in disasters: humanitarian and political. The humanitarian responsibilities imply provision of basic resources needed for the capacity to make autonomous choices (domestically and abroad), while the political responsibilities imply provision of the institutions needed for the liberal democratic citizenship (domestically). Through this analytical lens and building on the wealth of existing scholarship, we illustrate the disaster governance role of the American Red Cross in the United States (a 2005 hurricane) and in Haiti (the 2010 earthquake). Where, in Rawlsian terms, United States is interpreted as a âliberalâ society, Haiti is framed as a âburdenedâ society. The article proposes five points to consider in analyzing disaster governance arrangements under neoliberal regimes, structured around the division of humanitarian and political responsibilities. The article illustrates how NPOS are instrumental in blurring the boundaries between humanitarian and political responsibilities. This might result ultimately in actual vulnerabilities remaining unaddressed. While the Rawlsian approach challenges the privatization and lack of coordination in disaster governance, it is limited in analyzing the political construction of âburdenedâ societies
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