2,472 research outputs found
New approaches to probing Minkowski functionals
We generalize the concept of the ordinary skew-spectrum to probe the effect of non-Gaussianity
on the morphology of cosmic microwave background (CMB) maps in several domains: in
real space (where they are commonly known as cumulant-correlators), and in harmonic and
needlet bases. The essential aim is to retain more information than normally contained in these
statistics, in order to assist in determining the source of any measured non-Gaussianity, in the
same spirit as Munshi & Heavens skew-spectra were used to identify foreground contaminants
to the CMB bispectrum in Planck data. Using a perturbative series to construct the Minkowski
functionals (MFs), we provide a pseudo-C based approach in both harmonic and needlet
representations to estimate these spectra in the presence of a mask and inhomogeneous noise.
Assuming homogeneous noise, we present approximate expressions for error covariance for
the purpose of joint estimation of these spectra. We present specific results for four different
models of primordial non-Gaussianity local, equilateral, orthogonal and enfolded models, as
well as non-Gaussianity caused by unsubtracted point sources. Closed form results of nextorder
corrections to MFs too are obtained in terms of a quadruplet of kurt-spectra. We also
use the method of modal decomposition of the bispectrum and trispectrum to reconstruct the
MFs as an alternative method of reconstruction of morphological properties of CMB maps.
Finally, we introduce the odd-parity skew-spectra to probe the odd-parity bispectrum and its
impact on the morphology of the CMB sky. Although developed for the CMB, the generic
results obtained here can be useful in other areas of cosmology
Evidence for impurity-induced frustration in La2CuO4
Zero-field muon spin rotation and magnetization measurements were performed
in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by
M=Mg2+ spinless impurity. It is shown that while the doping dependence of the
sublattice magnetization (M(x)) is nearly the same for both compounds, the
N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the
Zn-doped compound. This difference, not taken into account within a simple
dilution model, is associated with the frustration induced by the Zn2+ impurity
onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin
stiffness is derived and found to be reduced by Zn doping more significantly
than expected within a dilution model. The effect of the structural
modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure
High pressure magnetic state of MnP probed by means of muon-spin rotation
We report a detailed SR study of the pressure evolution of the magnetic
order in the manganese based pnictide MnP, which has been recently found to
undergo a superconducting transition under pressure once the magnetic ground
state is suppressed. Using the muon as a volume sensitive local magnetic probe,
we identify a ferromagnetic state as well as two incommensurate helical states
(with propagation vectors aligned along the crystallographic and
directions, respectively) which transform into each other through first
order phase transitions as a function of pressure and temperature. Our data
appear to support that the magnetic state from which superconductivity develops
at higher pressures is an incommensurate helical phase.Comment: 11 pages, 9 figure
A Keyword, Taxonomy and Cartographic Research Review of Sustainability Concepts for Production Scheduling in Manufacturing Systems
The concept of sustainability is defined as composed of three pillars: social, environmental, and economic. Social sustainability implies a commitment to equity in terms of several “interrelated and mutually supportive” principles of a “sustainable society”; this concept includes attitude change, the Earth’s vitality and diversity conservation, and a global alliance to achieve sustainability. The social and environmental aspects of sustainability are related in the way sustainability indicators are related to “quality of life” and “ecological sustainability”. The increasing interest in green and sustainable products and production has influenced research interests regarding sustainable scheduling problems in manufacturing systems. This study is aimed both at reducing pollutant emissions and increasing production efficiency: this topic is known as Green Scheduling. Existing literature research reviews on Green Scheduling Problems have pointed out both theoretical and practical aspects of this topic. The proposed work is a critical review of the scientific literature with a three-pronged approach based on keywords, taxonomy analysis, and research mapping. Specific research questions have been proposed to highlight the benefits and related objectives of this review: to discover the most widely used methodologies for solving SPGs in manufacturing and identify interesting development models, as well as the least studied domains and algorithms. The literature was analysed in order to define a map of the main research fields on SPG, highlight mainstream SPG research, propose an efficient view of emerging research areas, propose a taxonomy of SPG by collecting multiple keywords into semantic clusters, and analyse the literature according to a semantic knowledge approach. At the same time, GSP researchers are provided with an efficient view of emerging research areas, allowing them to avoid missing key research areas and focus on emerging ones
Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO
Among the widely studied superconducting iron-pnictide compounds belonging to
the Ln1111 family (with Ln a lanthanide), a systematic investigation of the
crossover region between the superconducting and the antiferromagnetic phase
for the Ln = Nd case has been missing. We fill this gap by focusing on the
intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and
muon-spin spectroscopy measurements. The long-range order we detect at low
fluorine doping is replaced by short-range magnetic interactions at x = 0.08,
where also superconductivity appears. In this case, longitudinal-field
muon-spin spectroscopy experiments show clear evidence of slow magnetic
fluctuations that disappear at low temperatures. This fluctuating component is
ascribed to the glassy-like character of the magnetically ordered phase of
NdFeAsO at intermediate fluorine doping
A design methodology for an innovative racing mini motorcycle frame
Sports equipment design is a young and evolving engineering discipline focused on the best simultaneous optimization of user and product as a system. In motorsports, in particular, the final performance during a race depends on many parameters related to the vehicle, circuit, weather, and tyres and the personal feelings of every single driver. Top teams in high-tech categories can invest huge amounts of money in developing simulators, but such economic commitment is not sustainable for all those teams that operate in minor but very popular categories, such as karts or mini-motorcycles. In these fields, the most common design approach is trial and error on physical prototypes. Such an approach leads to high costs, long optimization times, poor innovation, and inefficient management of the design knowledge. The present paper proposes a driver centred methodology for the design of an innovative mini racing motorcycle frame. It consists of two main phases: the drivers’ feelings translation into engineering requirements and constraints, and the exploration of the design solution space. Expected effects of the application of the proposed methodology are an overall increase in the degree of innovation, time compression, and cost reduction during the development process, with a significant impact on the competitiveness of small racing teams in minor categories
Effect of two gaps on the flux lattice internal field distribution: evidence of two length scales from muSR in Mg1-xAlxB2
We have measured the transverse field muon spin precession in the flux
lattice (FL) state of the two gap superconductor MgB2 and of the electron doped
compounds Mg1-xAlxB2 in magnetic fields up to 2.8T. We show the effect of the
two gaps on the internal field distribution in the FL, from which we determine
two coherence length parameters and the doping dependence of the London
penetration depth. This is an independent determination of the complex vortex
structure already suggested by the STM observation of large vortices in a MgB2
single crystal. Our data agrees quantitatively with STM and we thus validate a
new phenomenological model for the internal fields.Comment: now in press Phys. Rev. Lett., small modifications required by the
edito
Understanding the SR spectra of MnSi without magnetic polarons
Transverse-field muon-spin rotation (SR) experiments were performed on a
single crystal sample of the non-centrosymmetric system MnSi. The observed
angular dependence of the muon precession frequencies matches perfectly the one
of the Mn-dipolar fields acting on the muons stopping at a 4a position of the
crystallographic structure. The data provide a precise determination of the
magnetic dipolar tensor. In addition, we have calculated the shape of the field
distribution expected below the magnetic transition temperature at the 4a
muon-site when no external magnetic field is applied. We show that this field
distribution is consistent with the one reported by zero-field SR studies.
Finally, we present ab initio calculations based on the density-functional
theory which confirm the position of the muon stopping site inferred from
transverse-field SR. In view of the presented evidence we conclude that
the SR response of MnSi can be perfectly and fully understood without
invoking a hypothetical magnetic polaron state.Comment: 10 pages, 12 figure
Tuning of competing magnetic and superconducting phase volumes in LaFeAsO$_0.945F_0.055 by hydrostatic pressure
The interplay between magnetism and superconductivity in LaFeAsO_0.945F_0.055
was studied as a function of hydrostatic pressure up to p~2.4GPa by means of
muon-spin rotation (\muSR) and magnetization measurements. The application of
pressure leads to a substantial decrease of the magnetic ordering temperature
T_N and a reduction of the magnetic phase volume and, at the same time, to a
strong increase of the superconducting transition temperature T_c and the
diamagnetic susceptibility. From the volume sensitive \muSR measurements it can
be concluded that the superconducting and the magnetic areas which coexist in
the same sample are inclined towards spatial separation and compete for phase
volume as a function of pressure.Comment: 4 pages, 4 figure
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