Optical Implementations Of Digital Algorithms For Pattern Recognition

Lee, Sing H.

doi:10.1117/12.7973781

Cited by 19 publications

(16 citation statements)

References 2 publications

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“…As a result, false horizontal fields or even dipolar structures are seen in unipolar plages with mostly vertical magnetic fields. To improve the local minimum structure solution, we identify the vertical magnetic field patterns using the algorithm of Lee (1986). The Lee technique uses a filter with width l and generates local neighborhood statistics in a box with size 2l þ 1.…”

Section: From the Local To A Global Azimuth Solutionmentioning

confidence: 99%

On the Resolution of the Azimuthal Ambiguity in Vector Magnetograms of Solar Active Regions

Georgoulis

Labonte

Metcalf

2004

ApJ

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We introduce a ''structure minimization'' technique to resolve the azimuthal ambiguity of 180 , intrinsic in solar vector magnetic field measurements. We resolve the 180 ambiguity by minimizing the inhomogeneities of the magnetic field strength perpendicular to the magnetic field vector. This relates to a minimization of the sheath currents that envelope the solar magnetic flux tubes, thus allowing for more space-filling and less complex magnetic fields. Structure minimization proceeds in two steps: First, it derives a local solution analytically, by means of a structure minimization function. Second, it reaches a global solution numerically, assuming smoothness of the magnetic field vector. Structure minimization (i) is disentangled from any use of potential or linear force-free extrapolations and (ii) eliminates pixel-to-pixel dependencies, thus reducing exponentially the required computations. We apply structure minimization to four active regions, located at various distances from disk center. The minimum structure solution for each case is compared with the ''minimum energy'' solution obtained by the slower simulated annealing algorithm. We find correlation coefficients ranging from significant to excellent. Moreover, structure minimization provides an ambiguity-free vertical gradient of the magnetic field strength that reveals the variation of the magnetic field with height. The simplicity and speed of the method allow a near real-time processing of solar vector magnetograms. This task was not possible in the past and may be of interest to both existing and future solar missions and ground-based magnetographs.

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Section: From the Local To A Global Azimuth Solutionmentioning

confidence: 99%

On the Resolution of the Azimuthal Ambiguity in Vector Magnetograms of Solar Active Regions

Georgoulis

Labonte

Metcalf

2004

ApJ

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“…The photon counting noise, which is white in the time domain, is removed by filtering ξ(t) once this is obtained from a Fourier back transform (see below). Our filters are implemented as Lee filters (Lee 1986) with sizes adapted to the expected noise, and the results are tested by eye for compatibility with the observed light curve.…”

Section: Estimation Of the Flare Profilementioning

confidence: 99%

Statistics of superimposed flares in the Taurus molecular cloud

Arzner¹,

Güdel²,

Briggs³

et al. 2007

A&A

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Context. Stochastically occurring flares provide a possible mechanism of coronal heating in magnetically active stars such as T Tauri objects in star-forming regions. Aims. We investigate the statistics of stellar X-ray light curves from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). Methods. To this end, the light curve is modeled as superimposed flares occurring at random times and with random amplitudes. The flare shape is estimated non-parametrically from the observations, while the flare amplitude distribution is modeled as a truncated power law, and the flare times are assumed as uniformly distributed. From these model assumptions, predictions on the binned counts are derived and compared with the observations. Results. From a sample of 22 XEST observations matching the above model assumptions we find that the majority of cases have flare amplitude distributions with slopes steeper than two. This favours the role of small flares in coronal heating for 5 targets, of which, however, 4 are foreground or background main-sequence stars.

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“…This was followed by the actual subtraction of the K s band image from the already scaled H 2 line image, which enabled us to identify pure H 2 1−0 S(1) shocked material, but excluded some of the weak "eye" detection. -Thirdly, before subtracting the K s band image from the already scaled H 2 line image, both images were processed with an IDL based routine LEEFILT originally implemented by Lee (1986), which is an enhancement process based on unsharp masking. Then, after the subtraction, the resulting image was smoothed with a 3-pixel box.…”

Section: Continuum Subtractionmentioning

confidence: 99%

An unbiased search for the signatures of protostars in the ρ Ophiuchi A molecular cloud

Khanzadyan¹,

Gredel²,

Smith³

et al. 2004

A&A

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Abstract. We present an unbiased search for molecular hydrogen emission in the L1688 cloud within the ρ Ophiuchi molecular cloud complex. Our near-infrared survey covers a connected region of extent 35 × 35 . We detect several new H 2 flows but the total number of detected outflows is low and is consistent with the paucity of Class 0 and Class 1 sources in the molecular cloud. From the spatial distribution, their collimation and the individual shapes of the bow shocks, we suggest possible candidates for the outflow sources. Most of the candidate driving sources are deeply embedded in dense cores of the molecular cloud. A very young outflow arises from the newly discovered Class 0 source MMS 126. Two major outflows in the NE-SW direction arise from the YLW 15 and YLW 16 Class I sources. Three additional outflows, which both extend over several arcminutes, arise from the Class I sources YLW 31 and YLW 52. Flow directions are generally NE-SW, perpendicular to the elongation directions of the cloud filaments. The apparent extents of molecular flows are related to either the widths of cloud filaments or to the separation between filaments. The estimated jet power needed to continuously drive and excite the detected portions of the shocked H 2 outflows lies in the range 0.02−0.2 L . Given the critical dependence on the environment, however, the total sizes and powers of the outflows may be considerably larger.

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Optical Implementations Of Digital Algorithms For Pattern Recognition

Cited by 19 publications

References 2 publications

On the Resolution of the Azimuthal Ambiguity in Vector Magnetograms of Solar Active Regions

On the Resolution of the Azimuthal Ambiguity in Vector Magnetograms of Solar Active Regions

Statistics of superimposed flares in the Taurus molecular cloud

An unbiased search for the signatures of protostars in the ρ Ophiuchi A molecular cloud

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