OALib Journal期刊

ISSN: 2333-9721



匹配條件: “Yousra Mazeh” ,找到相關結果約140條。
What Is Creativity and Why It Is So Important?  [PDF]
Yousra Mazeh
Open Access Library Journal (OALib Journal) , 2020, DOI: 10.4236/oalib.1105562
Abstract: Education is among the most important rights of children, which straightforwardly affects the learners’ life as it expands their awareness. This paper discusses how creative teachers encourage learners to think on their own so that not only their knowledge improves, but their interest, strength, team spirit and freedom of expression as well.
Ground-Based Photometric Searches for Transiting Planets
Tsevi Mazeh
Physics , 2009, DOI: 10.1017/S1743921308026185
Abstract: This paper reviews the basic technical characteristics of the ground-based photometric searches for transiting planets, and discusses a possible observational selection effect. I suggest that additional photometric observations of the already observed fields might discover new transiting planets with periods around 4-6 days. The set of known transiting planets support the intriguing correlation between the planetary mass and the orbital period suggested already in 2005.
Automatic local Gabor Features extraction for face recognition
Yousra Ben Jemaa,Sana Khanfir
Computer Science , 2009,
Abstract: We present in this paper a biometric system of face detection and recognition in color images. The face detection technique is based on skin color information and fuzzy classification. A new algorithm is proposed in order to detect automatically face features (eyes, mouth and nose) and extract their correspondent geometrical points. These fiducial points are described by sets of wavelet components which are used for recognition. To achieve the face recognition, we use neural networks and we study its performances for different inputs. We compare the two types of features used for recognition: geometric distances and Gabor coefficients which can be used either independently or jointly. This comparison shows that Gabor coefficients are more powerful than geometric distances. We show with experimental results how the importance recognition ratio makes our system an effective tool for automatic face detection and recognition.
Similarities Between the Inner Solar System and the Planetary System of PSR B1257+12
Tsevi Mazeh,Itzhak Goldman
Physics , 1994, DOI: 10.1086/133547
Abstract: We call attention to the surprising similarity between the newly discovered planetary system around PSR B1257+12 and the inner solar system. The similarity is in the ratios of the orbital radii and the masses of the three planets.
Detection of the ellipsoidal and the relativistic beaming effects in the CoRoT-3 lightcurve
Tsevi Mazeh,Simchon Faigler
Physics , 2010, DOI: 10.1051/0004-6361/201015550
Abstract: CoRoT-3b is a 22 Jupiter-mass massive-planet/brown-dwarf object, orbiting an F3-star with a period of 4.3 days. We analyzed the out-of-transit CoRoT-3 red-channel lightcurve obtained by the CoRoT mission and detected the ellipsoidal modulation, with half the orbital period and amplitude of 59+/-9 ppm (parts per million) and the relativistic beaming effect, with the orbital period and an amplitude of 27+/-9 ppm. Phases and amplitudes of both modulations were consistent with our theoretical approximation.
Photometric detection of non-transiting short-period low-mass companions through the beaming, ellipsoidal and reflection effects in Kepler and CoRoT lightcurves
Simchon Faigler,Tsevi Mazeh
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19011.x
Abstract: We present a simple algorithm, BEER, to search for a combination of the BEaming, Ellipsoidal and the Reflection/heating periodic modulations, induced by short-period non-transiting low-mass companions. The beaming effect is due to the increase (decrease) of the brightness of any light source approaching (receding from) the observer. To first order, the beaming and the reflection/heating effects modulate the stellar brightness at the orbital period, with phases separated by a quarter of a period, whereas the ellipsoidal effect is modulated with the orbital first harmonic. The phase and harmonic differences between the three modulations allow the algorithm to search for a combination of the three effects and identify stellar candidates for low-mass companions. The paper presents the algorithm, including an assignment of a likelihood factor to any possible detection, based on the expected ratio of the beaming and ellipsoidal effects, given an order-of-magnitude estimate of the three effects. As predicted by Loeb & Gaudi (2003) and Zucker, Mazeh & Alexander (2007), the Kepler and the CoRoT lightcurves are precise enough to allow detection of massive planets and brown-dwarf/low-mass-stellar companions with orbital period up to 10-30 days. To demonstrate the feasibility of the algorithm, we bring two examples of candidates found in the first 33 days of the Q1 Kepler lightcurves. Although we used relatively short timespan, the lightcurves were precise enough to enable the detection of periodic effects with amplitudes as small as one part in 10,000 of the stellar flux.
A Statistical Analysis of The Extrasolar Planets and The Low-Mass Secondaries
Tsevi Mazeh,Shay Zucker
Physics , 2002,
Abstract: We show that the astrometric Hipparcos data of the stars hosting planet candidates are not accurate enough to yield statistically significant orbits. Therefore, the recent suggestion, based on the analysis of the Hipparcos data, that the orbits of the sample of planet candidates are not randomly oriented in space, is not supported by the data. Assuming random orientation, we derive the mass distribution of the planet candidates and show that it is flat in log M, up to about 10 Jupiter masses. Furthermore, the mass distribution of the planet candidates is well separated from the mass distribution of the low-mass companions by the 'brown-dwarf desert'. This indicates that we have here two distinct populations, one which we identify as the giant planets and the other as stellar secondaries. We compare the period and eccentricity distributions of the two populations and find them surprisingly similar. The period distributions between 10 and 1650 days are flat in log period, indicating a scale-free formation mechanism in both populations. We further show that the eccentricity distributions are similar - both have a density distribution peak at about 0.2-0.4, with some small differences on both ends of the eccentricity range. We present a toy model to mimic both distributions. We found a significant paucity of massive giant planets with short orbital periods. The low frequency of planets is noticeable for masses larger than about 1 Jupiter Mass and periods shorter than 30 days. We point out how, in principle, one can account for this paucity.
Analysis of The Hipparcos Measurements of HD10697 - A Mass Determination of a Brown-Dwarf Secondary
Shay Zucker,Tsevi Mazeh
Physics , 2000, DOI: 10.1086/312523
Abstract: HD10697 is a nearby main-sequence star around which a planet candidate has recently been discovered by means of radial-velocity measurements (Vogt et al. 1999, submitted to ApJ). The stellar orbit has a period of about three years, the secondary minimum mass is 6.35 Jupiter masses and the minimum semi-major axis is 0.36 milli-arc-sec (mas). Using the Hipparcos data of HD10697 together with the spectroscopic elements of Vogt et al. (1999) we found a semi-major axis of 2.1 +/- 0.7 mas, implying a mass of 38 +/- 13 Jupiter masses for the unseen companion. We therefore suggest that the secondary of HD10697 is probably a brown dwarf, orbiting around its parent star at a distance of 2 AU.
Analysis of the Hipparcos Observations of the Extrasolar Planets and the Brown-Dwarf Candidates
Shay Zucker,Tsevi Mazeh
Physics , 2001, DOI: 10.1086/322959
Abstract: We analyzed the Hipparcos astrometric observations of 47 stars that were discovered to harbor giant planets and 14 stars with brown-dwarf secondary candidates. The Hipparcos measurements were used together with the corresponding stellar radial-velocity data to derive an astrometric orbit for each system. To find out the significance of the derived astrometric orbits we applied a "permutation" technique by which we analyzed the permuted Hipparcos data to get false orbits. The size distribution of these false orbits indicated the range of possibly random, false orbits that could be derived from the true data. These tests could not find any astrometric orbit of the planet candidates with significance higher than 99%, suggesting that most if not all orbits are not real. Instead, we used the Hipparcos data to set upper limits on the masses of the planet candidates. The lowest derived upper limit is that of 47UMa - 0.014 solar mass, which confirms the planetary nature of its unseen companion. For 13 other planet candidates the upper limits exclude the stellar nature of their companions, although brown-dwarf secondaries are still an option. These negate the idea that all or most of the extrasolar planets are disguised stellar secondaries. Of the 14 brown-dwarf candidates, our analysis reproduced the results of Halbwachs et al., who derived significant astrometric orbits for 6 systems which imply secondaries with stellar masses. We show that another star, HD164427, which was discovered only very recently, also has a secondary with stellar mass. Our findings support Halbwachs et al. conclusion about the possible existence of the "brown-dwarf desert" which separates the planets and the stellar secondaries.
Derivation of the Mass Distribution of Extrasolar Planets with MAXLIMA - a Maximum Likelihood Algorithm
Shay Zucker,Tsevi Mazeh
Physics , 2001, DOI: 10.1086/323866
Abstract: We construct a maximum-likelihood algorithm - MAXLIMA, to derive the mass distribution of the extrasolar planets when only the minimum masses are observed. The algorithm derives the distribution by solving a numerically stable set of equations, and does not need any iteration or smoothing. Based on 50 minimum masses, MAXLIMA yields a distribution which is approximately flat in log M, and might rise slightly towards lower masses. The frequency drops off very sharply when going to masses higher than 10 Jupiter masses, although we suspect there is still a higher mass tail that extends up to probably 20 Jupiter masses. We estimate that 5% of the G stars in the solar neighborhood have planets in the range of 1-10 Jupiter masses with periods shorter than 1500 days. For comparison we present the mass distribution of stellar companions in the range of 100--1000 Jupiter masses, which is also approximately flat in log M. The two populations are separated by the "brown-dwarf desert", a fact that strongly supports the idea that these are two distinct populations. Accepting this definite separation, we point out the conundrum concerning the similarities between the period, eccentricity and even mass distribution of the two populations.

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