343 research outputs found
Helical Magnetic Fields in Molecular Clouds? A New Method to Determine the Line-of-Sight Magnetic Field Structure in Molecular Clouds
Magnetic fields pervade in the interstellar medium (ISM) and are believed to
be important in the process of star formation, yet probing magnetic fields in
star formation regions is challenging. We propose a new method to use Faraday
rotation measurements in small scale star forming regions to find the direction
and magnitude of the component of magnetic field along the line-of-sight. We
test the proposed method in four relatively nearby regions of Orion A, Orion B,
Perseus, and California. We use rotation measure data from the literature. We
adopt a simple approach based on relative measurements to estimate the rotation
measure due to the molecular clouds over the Galactic contribution. We then use
a chemical evolution code along with extinction maps of each cloud to find the
electron column density of the molecular cloud at the position of each rotation
measure data point. Combining the rotation measures produced by the molecular
clouds and the electron column density, we calculate the line-of-sight magnetic
field strength and direction. In California and Orion A, we find clear evidence
that the magnetic fields at one side of these filamentary structures are
pointing towards us and are pointing away from us at the other side. Even
though the magnetic fields in Perseus might seem to suggest the same behavior,
not enough data points are available to draw such conclusions. In Orion B, as
well, there are not enough data points available to detect such behavior. This
behavior is consistent with a helical magnetic field morphology. In the
vicinity of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud
Barnard 1, we find magnetic field values of G, G,
and G, respectively, which are in agreement with the Zeeman
Measurements
On the computation of zeros of Bessel functions
The zeros of some chosen Bessel functions of different orders is revised using the well-known bisection method , McMahon formula is also reviewed and the calculation of some zeros are carried out implementing a recent version of MATLAB software.
The obtained results are analyzed and discussed on the lights of previous calculations
Smoothed Bootstrap Methods for Hypothesis Testing
This paper demonstrates the application of smoothed bootstrap methods and Efron’s methods for hypothesis testing on real-valued data, right-censored data and bivariate data. The tests include quartile hypothesis tests, two sample medians and Pearson and Kendall correlation tests. Simulation studies indicate that the smoothed bootstrap methods outperform Efron’s methods in most scenarios, particularly for small datasets. The smoothed bootstrap methods provide smaller discrepancies between the actual and nominal error rates, which makes them more reliable for testing hypotheses
Wavelets operational methods for fractional differential equations and systems of fractional differential equations
In this thesis, new and effective operational methods based on polynomials and
wavelets for the solutions of FDEs and systems of FDEs are developed. In particular
we study one of the important polynomial that belongs to the Appell family of
polynomials, namely, Genocchi polynomial. This polynomial has certain great
advantages based on which an effective and simple operational matrix of derivative
was first derived and applied together with collocation method to solve some singular
second order differential equations of Emden-Fowler type, a class of generalized
Pantograph equations and Delay differential systems. A new operational matrix of
fractional order derivative and integration based on this polynomial was also
developed and used together with collocation method to solve FDEs, systems of
FDEs and fractional order delay differential equations. Error bound for some of the
considered problems is also shown and proved. Further, a wavelet bases based on
Genocchi polynomials is also constructed, its operational matrix of fractional order
derivative is derived and used for the solutions of FDEs and systems of FDEs. A
novel approach for obtaining operational matrices of fractional derivative based on
Legendre and Chebyshev wavelets is developed, where, the wavelets are first
transformed into corresponding shifted polynomials and the transformation matrices
are formed and used together with the polynomials operational matrices of fractional
derivatives to obtain the wavelets operational matrix. These new operational matrices
are used together with spectral Tau and collocation methods to solve FDEs and
systems of FDEs
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