fitting procedure
Recently Published Documents


TOTAL DOCUMENTS

603
(FIVE YEARS 114)

H-INDEX

45
(FIVE YEARS 5)

2022 ◽  
Vol 55 (1) ◽  
Author(s):  
J. K. Jochum ◽  
L. Spitz ◽  
C. Franz ◽  
A. Wendl ◽  
J. C. Leiner ◽  
...  

A method is reported to determine the phase and amplitude of sinusoidally modulated event rates, binned into four bins per oscillation, based on data generated at the resonant neutron spin-echo spectrometer RESEDA at FRM-II. The presented algorithm relies on a reconstruction of the unknown parameters. It omits a calculation-intensive fitting procedure and avoids contrast reduction due to averaging effects. It allows the current data acquisition bottleneck at RESEDA to be relaxed by a factor of four and thus increases the potential time resolution of the detector by the same factor. The approach is explained in detail and compared with the established fitting procedures of time series having four and 16 time bins per oscillation. In addition the empirical estimates of the errors of the three methods are presented and compared with each other. The reconstruction is shown to be unbiased, asymptotic and efficient for estimating the phase. Reconstructing the contrast increases the error bars by roughly 10% as compared with fitting 16 time-binned oscillations. Finally, the paper gives heuristic, analytical equations to estimate the error for phase and contrast as a function of their initial values and counting statistics.


Author(s):  
Eckhard Liebscher ◽  
Franziska Taubert ◽  
David Waltschew ◽  
Jessica Hetzer

AbstractModelling and applying multivariate distributions is an important topic in ecology. In particular in plant ecology, the multidimensional nature of plant traits comes with challenges such as wide ranges in observations as well as correlations between several characteristics. In other disciplines (e.g., finances and economics), copulas have been proven as a valuable tool for modelling multivariate distributions. However, applications in ecology are still rarely used. Here, we present a copula-based methodology of fitting multivariate distributions to ecological data. We used product copula models to fit multidimensional plant traits, on example of observations from the global trait database TRY. The fitting procedure is split into two parts: fitting the marginal distributions and fitting the copula. We found that product copulas are well suited to model ecological data as they have the advantage of being asymmetric (similar to the observed data). Challenges in the fitting were mainly addressed to limited amount of data. In view of growing global databases, we conclude that copula modelling provides a great potential for ecological modelling.


2022 ◽  
Vol 130 (3) ◽  
pp. 345
Author(s):  
А.В. Кузнецов ◽  
Н.И. Распопова ◽  
О.В. Громова ◽  
Е.С. Бехтерева ◽  
М.А. Кошелев ◽  
...  

The high-resolution spectrum of the 72GeH4 molecule was recorded on a Bruker IFS 125HR Fourier spectrometer with an optical resolution of 0.003 cm-1. The line positions were analyzed for ten interacting vibrational-rotational bands 3ν4 (1F2, F1, 2F2), v2+ 2ν4 (1E, F1, F2, 2E) and 2ν2+v4 (1F2, F1, 2F2) in the range 2350-2750 cm-1. As a result of the analysis, 1726 experimental lines were identified with the maximum value of the quantum number Jmax = 17; then used in the fitting procedure with parameters of the effective Hamiltonian. The resulting set of 35 spectroscopic parameters describes the vibrational-rotational structure of the spectrum with drms = 7.5 · 10-4 cm-1.


2021 ◽  
Vol 258 (1) ◽  
pp. 9
Author(s):  
Li-Li Wang ◽  
Shi-Yin Shen ◽  
A-Li Luo ◽  
Guang-Jun Yang ◽  
Ning Gai ◽  
...  

Abstract We first derive the stellar population properties: age and metallicity for ∼43,000 low redshift galaxies in the DR7 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, which have no spectroscopic observations in the Sloan Digital Sky Survey (SDSS). We employ a fitting procedure based on the small-scale features of galaxy spectra so as to avoid possible biases from the uncertain flux calibration of the LAMOST spectroscopy. We show that our algorithm can successfully recover the average age and metallicity of the stellar populations of galaxies down to signal-to-noise ratio ≥5 through testing on both mock galaxies and real galaxies comprising LAMOST and their SDSS counterparts. We provide a catalog of the age and metallicity for ∼43,000 LAMOST galaxies online. As a demonstration of the scientific application of this catalog, we present the Holmberg effect on both age and metallicity of a sample of galaxies in galaxy pairs.


Author(s):  
Bojana Ilic ◽  
Dusan Zigic ◽  
Marko Djordjevic ◽  
Magdalena Djordjevic

The scarce knowledge of the initial stages of quark-gluon plasma before the thermalization is mostly inferred through the low-[Formula: see text] sector. We propose a complementary approach in this report — the use of high-[Formula: see text] probes’ energy loss. We study the effects of four commonly assumed initial stages, whose temperature profiles differ only before the thermalization, on high-[Formula: see text][Formula: see text] and [Formula: see text] predictions. The predictions are based on our Dynamical Radiative and Elastic ENergy-loss Approach (DREENA) framework. We report insensitivity of [Formula: see text] to the initial stages, making it unable to distinguish between different cases. [Formula: see text] displays sensitivity to the presumed initial stages, but current experimental precision does not allow resolution between these cases. We further revise the commonly accepted procedure of fitting the energy loss parameters, for each individual initial stage, to the measured [Formula: see text]. We show that the sensitivity of [Formula: see text] to various initial stages obtained through such procedure is mostly a consequence of fitting procedure, which may obscure the physical interpretations. Overall, the simultaneous study of high-[Formula: see text] observables, with unchanged energy loss parametrization and restrained temperature profiles, is crucial for future constraints on initial stages.


Author(s):  
Cosimo Aliani ◽  
Eva Rossi ◽  
Piergiorgio Francia ◽  
Leonardo Bocchi

Abstract Objective:Vascular ageing is associated with several alterations, including arterial stiffness and endothelial dysfunction. Such alterations represent an independent factor in the development of cardiovascular disease. In our previous works we demonstrated the alterations occurring in the vascular system are themselves reflected in the shape of the peripheral waveform; thus, a model that describes the waveform as a sum of Gaussian curves provides a set of parameters that successfully discriminate between under(<= 35 years old) and over subjects (> 35 years old). In the present work, we explored the feasibility of a new decomposition model, based on a sum of exponential pulses, applied to the same problem. Approach: The first processing step extracts each pulsation from the input signal and removes the long-term trend using a cubic spline with nodes between consecutive pulsations. After that, a Least Squares fitting algorithm determines the set of optimal model parameters that best approximates each single pulse. The vector of model parameters gives a compact representation of the pulse waveform that constitutes the basis for the classification step. Each subject is associated to his/her "representative" pulse waveform, obtained by averaging the vector parameters corresponding to all pulses. Finally, a Bayesan classifier has been designed to discriminate the waveforms of under and over subjects, using the leave-one-subject-out validation method. Main results: Results indicate that the fitting procedure reaches a rate of 96% in under subjects and 95% in over subjects and that the Bayesan classifier is able to correctly classify 91\% of the subjects with a specificity of 94% and a sensibility of 84%. Significance: This study shows a sensible vascular age estimation accuracy with a multi-exponential model, which may help to predict cardiovascular diseases.


Author(s):  
Sajedah Alalmeer ◽  
M I Jaghoub ◽  
Ibrahim Naji Ghabar

Abstract In this work we study nucleon-nucleus elastic scattering using a nonlocal, velocity-dependent optical potential. The potential parameters are determined by fitting elastic angular distributions and polarization data for nucleon scattering off a wide range of nuclei falling in the mass range $12 \leq A \leq 208$ and over the energy range 10 - 60 MeV. Our potential parameters lead to smoothly varying local equivalent potentials and, unlike previous works, the potential depths corresponding to the real volume, imaginary surface, and imaginary volume terms show systematic linear dependences on energy. In addition, for each nuclear target, we determined constant sets of geometric parameters. Including the polarization data in the fitting procedure helped in reducing the large variations in the depths of the spin-orbit term. Our best-fit angular distributions and polarization data are in very good agreement with measured data, and are either as good as the cross sections obtained with widely-used systematics or better.


Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6690
Author(s):  
Amir Mohammad Mirzaei ◽  
Mauro Corrado ◽  
Alberto Sapora ◽  
Pietro Cornetti

Interfacial debonding in fiber-reinforced composites is a common problem, especially in external strengthening techniques. This investigation aims to determine the load during debonding, and discusses two practical design parameters for direct shear tests, which are commonly used to assess the mechanics of debonding. In this study, three different bond-slip cohesive laws and one finite fracture mechanics approach are considered to investigate debonding in direct shear tests by taking the effect of residual strength into account. For each model, load during debonding and its maximum value are given by closed-form expressions, which are then checked against experimental data reported in the literature. It is shown that using the interfacial mechanical properties extracted from one geometry, the debonding load of tests with different bond lengths and widths can be predicted without any fitting procedure. Moreover, effective bond length formulae are suggested for each model; one is the straightforward extension (accounting for residual strength) of a formula available in the Standards. The results illustrate the importance of considering residual strength in direct shear tests, even at debonding onset, with its effect being nonetheless higher for long bond lengths.


2021 ◽  
Vol 2090 (1) ◽  
pp. 012135
Author(s):  
F Mauro ◽  
R Nabergoj

Abstract The execution of the so-called extinction tests represents the classical experimental method used to estimate the damping of an oscillatory system. For the specific case of ship roll motion, the roll decay tests are carried out at model-scale in a hydrodynamic basin. During these tests, the vessel is posed in an imbalance condition by an external moment and, after the release, the motion decays to the equilibrium condition. When the damping is far below the critical one, the transient decay is oscillatory. Here a new methodology is presented to determine the damping coefficients by fitting the roll decay curves directly, using a least-square fitting through a differential evolution algorithm of global optimisation. The results obtained with this methodology are compared with the predictions from standard methods. This kind of approach seems to be very promising when the motion model of the system under investigation is established with any level of non-linearities included. The usage of the fitting procedure on the approximate analytic solution of the differential equation of motion demonstrates the flexibility of the method. As a benchmark example, two experimentally measured roll extinction curves have been considered and suitably fitted. The newly predicted results, compared with the ones obtained from standard roll decay analysis, show that the algorithm is capable to perform a good regression on the experimental data.


Sign in / Sign up

Export Citation Format

Share Document