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Search Results: 1 - 10 of 34983 matches for " Jian Ge "
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An all-sky extrasolar planet survey with multiple object, dispersed fixed-delay interferometers
Jian Ge
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: La prospección de planetas extrasolares en todo el cielo (ASEPS) se basará en telescopios de campo amplio (inicialmente el telescopio Sloan, para luego pasar a telescopios con mayores aperturas) y una nueva generación de potentes espectrógrafos multiobjetos para dar seguimiento a millones de estrellas brillantes cercanas. ASEPS detectará decenas de miles de planetas extrasolares en las próximas dos décadas. Actualmente, ya se ha detectado un planeta (con periodo de 4.11 días y con 0.49 masas de Júpiter) alrededor de una estrella de V = 8.05 mag (Ge et al. 2006), con el telescopio de 0.9-m Coude del KPNO, con el instrumento interferométrico de retardo fijo dispersado en su version mono-objeto. En las bandas visibles, ASEPS incrementará el número de sistemas planetarios en al menos dos órdenes de magnitud, dando así una poderosa base estad′ stica para comprender las diferentes clases de sistemas planetarios. Este estudio tiene la capacidad de detectar planetas tipo Júpiter, tanto en masa como en distancia a su estrella madre. El estudio se desarrolla en el cercano infrarrojo y puede conducir al descubrimiento de planetas tipo terrestre en las zonas habitables de estrellas poco masivas. Las observaciones recientes con el telescopio Sloan demuestran la viabilidad de la búsqueda de planetas en forma multi-objeto en paralelo al reconocimiento espectroscópico de objetos d′ebiles SDSS. Esto sugiere que es posible combinar instrumentos Doppler con otros instrumentos astronómicos dentro de un solo paquete para incrementar la productividad científica y la eficiencia de operación, y así reducir los costos de instrumentos de los futuros grandes telescopios de campo amplio
Fixed-delay Interferometry for Doppler Extra-solar Planet Detection
Jian Ge
Physics , 2002, DOI: 10.1086/341226
Abstract: We present a new technique based on fixed-delay interferometry for high throughput, high precision and multi-object Doppler radial velocity (RV) surveys for extra-solar planets. The Doppler measurements are conducted through monitoring the stellar fringe phase shifts of the interferometer. High Doppler sensitivity is achieved through optimizing the optical delay in the interferometer and reducing photon noise by measuring multiple fringes over a broadband. This broadband operation is performed through coupling the interferometer with a low to medium resolution post-disperser. The total Doppler sensitivity of this approach is, in theory, independent of dispersing power of the post-disperser, which allows development of new generation RV machines with much reduced size, high stability and low cost compared to echelles. This technique has the potential to improve RV survey efficiency by 2-3 orders of magnitude over cross-dispersed echelle spectroscopy approach to allow a full sky RV survey for planets once the instrument is operated as a multi-object instrument and optimized for high throughput. The simple interferometer response potentially allows this technique to be operated at other wavelengths independent of popular iodine reference sources to search for planets around early type stars, white dwarfs, and M, L and T dwarfs for the first time.
Soul Theorem for 4-dimensional Topologically Regular Open Nonnegatively Curved Alexandrov Spaces
Jian Ge
Mathematics , 2010,
Abstract: In this paper, we study the topology of topologically regular 4-dimensional open non-negatively curved Alexandrov spaces. These spaces occur naturally as the blow-up limits of compact Riemannian manifolds with lower curvature bound. These manifolds have also been studied by Yamaguchi in his preprint [Yam2002]. Our main tools are gradient flows of semi-concave functions and critical point theory for distance functions, which have been used to study the 3-dimensional collapsing theory in the paper [CaoG2010]. The results of this paper will be used in our future studies of collapsing 4-manifolds, which will be discussed elsewhere.
Comparison Theorems for Manifold with Mean Convex Boundary
Jian Ge
Mathematics , 2013, DOI: 10.1142/S0219199715500108
Abstract: Let $M^n$ be an $n$-dimensional Riemannian manifold with boundary $\partial M$. Assume that Ricci curvature is bounded from below by $(n-1)k$, for $k\in \RR$, we give a sharp estimate of the upper bound of $\rho(x)=\dis(x, \partial M)$, in terms of the mean curvature bound of the boundary. When $\partial M$ is compact, the upper bound is achieved if and only if $M$ is isometric to a disk in space form. A Kaehler version of estimation is also proved. Moreover we prove a Laplace comparison theorem for distance function to the boundary of Kaehler manifold and also estimate the first eigenvalue of the real Laplacian.
Molecular Hydrogen Absorption in the z= 1.97 Damped Lyman alpha Absorption system toward QSO 0013-004
Jian Ge,Jill Bechtold
Physics , 1997, DOI: 10.1086/310527
Abstract: We present a new ultra-violet spectrum of the QSO 0013-004 with 0.9 \AA resolution obtained with the MMT Blue spectrograph. The \upsilon = 0 - 0, 1 - 0, 2 - 0 and 3 - 0 Lyman bands of H_2 associated with the z = 1.9731 damped Ly alpah absorption line system have been detected. The H_2 column density is N(H_2) = 6.9 (\pm 1.6)\times 10^{19} cm^{-2}, and the Doppler parameter b = 15\pm 2 km/s. The populations of different rotational levels are measured and used to derive the excitation temperatures. The estimated kinetic temperature T_K\sim 70 K, and the total particle number density n(H) \sim 300 cm^{-3}. The UV photoabsorption rate $\beta_0 \sim 6.7\times 10^{-9}$ s^{-1}, about a factor of few times greater than that in a typical diffuse Milky Way interstellar cloud. The total hydrogen column density is $N(H) = 6.4(\pm 0.5)\times 10^{20} cm^{-2}$. The fractional H_2 abundance f = 2N(H_2)/(2N(H_2) + N(H I)) \sim 0.22 \pm 0.05 is the highest among all observed damped Ly\al absorbers. The high fractional H_2 abundance is consistent with the inferred presence of dust and strong C I absorption in this absorber.
How Close Are We To Detecting Earth-like Planets in the Habitable Zone Using the Radial Velocity Technique?
Ji Wang,Jian Ge
Physics , 2011,
Abstract: Discovering an Earth-like exoplanet in habitable zone is an important milestone for astronomers in search of extra-terrestrial life. While the radial velocity (RV) technique remains one the most powerful tools in detecting and characterizing exo-planetary sys- tems, we calculate the uncertainties in precision RV measurements considering stellar spectral quality factors, RV calibration sources, stellar noise and telluric contamination in different observational bandpasses and for different spectral types. We predict the optimal observational bandpass for different spectral types using the RV technique un- der a variety of conditions. We compare the RV signal of an Earth-like planet in the habitable zone (HZ) to the near future state of the art RV precision and attempt to answer the question: How close are we to detecting Earth-like planet in the HZ using the RV technique?
Page charge of D-branes and its behavior in topologically nontrivial B-fields
Jian-Ge Zhou
Physics , 2001, DOI: 10.1103/PhysRevD.64.066003
Abstract: The RR Page charges for the D(2p+1)-branes with B-field in type IIB supergravity are constructed consistently from brane source currents. The resulting Page charges are B-independent in the nontrivial and intricate way. It is found that in topologically trivial B-field the Page charge is conserved, but in the topologically nontrivial B-field it is no longer to be conserved, instead there is a jump between two Page charges defined in each patch, and we interpret this jump as Hanany-Witten effect.
PP-wave String Interactions from String Bit Model
Jian-Ge Zhou
Physics , 2002, DOI: 10.1103/PhysRevD.67.026010
Abstract: We construct the string states $|O_{p}^J>_J$, $|O_{q}^{J_1}>_{{J_1}{J_2}}$ and $|O_{0}^{J_{1}J_{2}}>_{{J_1}{J_2}}$ in the Hilbert space of the quantum mechanical orbifold model so as to calculate the three point functions and the matrix elements of the light-cone Hamiltonian from the interacting string bit model. With these string states we show that the three point functions and the matrix elements of the Hamiltonian derived from the interacting string bit model up to $g^{2}_2$ order precisely match with those computed from the perturbative SYM theory in BMN limit.
Statistical Properties of Brown Dwarf Companions: Implications for Different Formation Mechanisms
Bo Ma,Jian Ge
Physics , 2013, DOI: 10.1093/mnras/stu134
Abstract: The mass domain where massive extrasolar planets and brown dwarfs overlap is still poorly understood due to the paucity of brown dwarfs orbiting close to solar-type stars, the so-called brown dwarf desert. In this paper we collect all of available data about close brown dwarfs around solar type stars and their host stars from literature and study the demographics of the brown dwarf desert. The data clearly show a short period and a medium mass gap in the brown dwarf period-mass distribution diagram ($ 35
Super 0-brane and GS Superstring Actions on AdS_2 \times S^2
Jian-Ge Zhou
Physics , 1999, DOI: 10.1016/S0550-3213(99)00462-9
Abstract: The super 0-brane and GS superstring actions on AdS$_2 \times S^2$ background with 2-form flux are constructed by supercoset approach. We find the super 0-brane action contains two parameters which are interpreted as the electric and magnetic charges of the super 0-brane. The obtained super 0-brane action describes the BPS saturated dyonic superparticle moving on AdS$_2 \times S^2$ background. The WZ action contains the required coupling with 2-form flux. For GS superstring, we find the string action on AdS$_2 \times S^2$ takes the same form as those in AdS$_3 \times S^3$ and AdS$_5 \times S^5$ with RR field background.
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