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arXivObservations and Theory of Dynamical Triggers for Star Formation B. G. Elmegreen 19971231 Star formation triggering mechanisms are reviewed, including the direct compression of clouds and globules, the compression and collapse of molecular clouds at the edges of HII regions and supernovae, the expansion and collapse of giant rings and shells in galaxy disks, and the collision and collapse between two clouds. Collapse criteria are given. A comprehensive tabulation of regions where these four types of triggering have been found suggests that dynamical processes sustain and amplify a high fraction of all star formation that begins spontaneously in normal galaxy disks.
Subject Source arXiv URL https://arxiv.org/abs/astroph/9712352view Article Title Observations and Theory of Dynamical Triggers for Star FormationAuthors B. G. ElmegreenAbstract Star formation triggering mechanisms are reviewed, including the direct compression of clouds and globules, the compression and collapse of molecular clouds at the edges of HII regions and supernovae, the expansion and collapse of giant rings and shells in galaxy disks, and the collision and collapse between two clouds. Collapse criteria are given. A comprehensive tabulation of regions where these four types of triggering have been found suggests that dynamical processes sustain and amplify a high fraction of all star formation that begins spontaneously in normal galaxy disks.Is Part Of 19971231 Identifier ISSN: Category astrophLicense 
arXivGeometric statistical inference Vipul Periwal 19971231 Finite sample size corrections to the reparametrizationinvariant solution of the inverse problem of probability are computed, and shown to converge uniformly to the correct distribution.
Subject Source arXiv URL https://arxiv.org/abs/adaporg/9801001view Article Title Geometric statistical inferenceAuthors Vipul PeriwalAbstract Finite sample size corrections to the reparametrizationinvariant solution of the inverse problem of probability are computed, and shown to converge uniformly to the correct distribution.Is Part Of 19971231 Identifier ISSN: Category adaporg nlin.AOLicense 
arXivSurveying the Hard Xray Sky: Imaging in Space and Time Jonathan E. Grindlay 19971231 One of the few remaining astronomical bands (factor of $\sim$10 in energy range) still without an allsky imaging survey is the hard xray band (10600 keV). This is in spite of sensitive imaging allsky surveys already conducted at soft xray energies (0.22 keV; ROSAT) and soft/hard $\gamma$ray ($\sim$750 keV  10 GeV; COMPTEL/EGRET) energies and imminent for medium xray energies (2 10 keV; ABRIXAS). A Hard xray imaging survey conducted with widefield coded aperture telescopes allows both high sensitivity (and spatial/spectral resolution) and broad temporal coverage. We derive a generalized survey sensitivity/temporal parameter, Q, and compare previous and planned hard xray surveys with the proposed EXIST mission. Key scientific objectives that could be addressed with the enhanced capability of EXIST are outlined.
Subject Source arXiv URL https://arxiv.org/abs/astroph/9712360view Article Title Surveying the Hard Xray Sky: Imaging in Space and TimeAuthors Jonathan E. GrindlayAbstract One of the few remaining astronomical bands (factor of $\sim$10 in energy range) still without an allsky imaging survey is the hard xray band (10600 keV). This is in spite of sensitive imaging allsky surveys already conducted at soft xray energies (0.22 keV; ROSAT) and soft/hard $\gamma$ray ($\sim$750 keV  10 GeV; COMPTEL/EGRET) energies and imminent for medium xray energies (2 10 keV; ABRIXAS). A Hard xray imaging survey conducted with widefield coded aperture telescopes allows both high sensitivity (and spatial/spectral resolution) and broad temporal coverage. We derive a generalized survey sensitivity/temporal parameter, Q, and compare previous and planned hard xray surveys with the proposed EXIST mission. Key scientific objectives that could be addressed with the enhanced capability of EXIST are outlined.Is Part Of 19971231 Identifier ISSN: DOI 10.1002/asna.2123190160Category astrophLicense 
arXivProposed (to) EXIST: Hard Xray Imaging All Sky Survey/Monitor J. E. Grindlay, T. A. Prince, F. Harrison, ... more(9) 19971231 The hard xray (10600 keV) sky is inherently time variable and yet has neither been surveyed nor monitored with a sensitive imaging telescope. The Energetic Xray Imaging Survey Telescope (EXIST) is a mission concept, proposed for MIDEX, which would conduct the first imaging allsky hard xray survey as well as provide a sensitive all sky monitor. With $\sim 60%$ sky coverage each orbit, and full sky coverage each 50 days, hard xray studies of gammaray bursts, AGN, galactic transients, xray binaries and accretionpowered pulsars can be conducted over a wide range of timescales. We summarize the scientific objectives of EXIST for both the survey and monitoring objectives. We describe the mission concept and the instrumentation approach, which would incorporate a large area array of CdZnTe (CZT) detectors, as well as some of our ongoing development of CZT array detectors.
Subject Source arXiv URL https://arxiv.org/abs/astroph/9712359view Article Title Proposed (to) EXIST: Hard Xray Imaging All Sky Survey/MonitorAuthors J. E. Grindlay; T. A. Prince; F. Harrison; N. Gehrels; C. J. Hailey; B. Ramsey; M. C. Weisskopf; G. K. Skinner; P. UbertiniAbstract The hard xray (10600 keV) sky is inherently time variable and yet has neither been surveyed nor monitored with a sensitive imaging telescope. The Energetic Xray Imaging Survey Telescope (EXIST) is a mission concept, proposed for MIDEX, which would conduct the first imaging allsky hard xray survey as well as provide a sensitive all sky monitor. With $\sim 60%$ sky coverage each orbit, and full sky coverage each 50 days, hard xray studies of gammaray bursts, AGN, galactic transients, xray binaries and accretionpowered pulsars can be conducted over a wide range of timescales. We summarize the scientific objectives of EXIST for both the survey and monitoring objectives. We describe the mission concept and the instrumentation approach, which would incorporate a large area array of CdZnTe (CZT) detectors, as well as some of our ongoing development of CZT array detectors.Is Part Of 19971231 Identifier ISSN: Category astrophLicense 
arXivSmallScale Mixing of the Elements Bruce G. Elmegreen 19971231 The progressive mixing and contamination of interstellar gas by supernovae and other processes following the passage of a spiral density wave is reviewed, with an emphasis on the Solar neighborhood. Regions of star formation should begin their lives with an inhomogeneous mixture of abundances as a result of their chaotic and largescale formation processes. These inhomogeneities should continue to increase during several generations of star formation until the gas enters the interarm region. Then cloud dispersal by large interarm tidal forces, high rates of shear, and internal star formation should all lead to cloudtocloud mixing, while increased ionization, heating, and evaporation should lead to mixing on the atomic level. Gradients in the dispersion of elemental abundances are expected for galaxy disks.
Subject Source arXiv URL https://arxiv.org/abs/astroph/9712354view Article Title SmallScale Mixing of the ElementsAuthors Bruce G. ElmegreenAbstract The progressive mixing and contamination of interstellar gas by supernovae and other processes following the passage of a spiral density wave is reviewed, with an emphasis on the Solar neighborhood. Regions of star formation should begin their lives with an inhomogeneous mixture of abundances as a result of their chaotic and largescale formation processes. These inhomogeneities should continue to increase during several generations of star formation until the gas enters the interarm region. Then cloud dispersal by large interarm tidal forces, high rates of shear, and internal star formation should all lead to cloudtocloud mixing, while increased ionization, heating, and evaporation should lead to mixing on the atomic level. Gradients in the dispersion of elemental abundances are expected for galaxy disks.Is Part Of 19971231 Identifier ISSN: Category astrophLicense 
arXivClassical and nonclassical symmetries of a generalized Boussinesq equation Maria Luz Gandarias, M. S. Bruzón 19971231 We apply the Liegroup formalism and the nonclassical method due to Bluman and Cole to deduce symmetries of the generalized Boussinesq equation, which has the classical Boussinesq equation as an special case. We study the class of functions $f(u)$ for which this equation admit either the classical or the nonclassical method. The reductions obtained are derived. Some new exact solutions can be derived.
Subject 수학 Source arXiv URL https://arxiv.org/abs/mathph/9801206view Article Title Classical and nonclassical symmetries of a generalized Boussinesq equationAuthors Maria Luz Gandarias; M. S. BruzónAbstract We apply the Liegroup formalism and the nonclassical method due to Bluman and Cole to deduce symmetries of the generalized Boussinesq equation, which has the classical Boussinesq equation as an special case. We study the class of functions $f(u)$ for which this equation admit either the classical or the nonclassical method. The reductions obtained are derived. Some new exact solutions can be derived.Is Part Of J. Nonlinear Math. Phys. 5 (1998), no. 1, 812 19971231 Identifier ISSN: DOI 10.2991/jnmp.1998.5.1.2Category mathph math.AP math.MPLicense 
arXivLorentz symmetry violation at Planck scale, cosmology and superluminal particles Luis GonzalezMestres 19971231 Although Lorentz symmetry has been tested at low energy with extremely good accuracy, its validity at very high energy is much less well established. If Lorentz symmetry violation (LSV) is energydependent (e.g. $\propto E^2$), it can be of order 1 at Planck scale and undetectable at GeV scale or below. Similarly, superluminal particles with positive mass and energy (superbradyons) can exist and be the ultimate building blocks of matter. We discuss a few cosmological consequences of such a scenario, as well as possible experimental tests.
Subject Source arXiv URL https://arxiv.org/abs/physics/9712056view Article Title Lorentz symmetry violation at Planck scale, cosmology and superluminal particlesAuthors Luis GonzalezMestresAbstract Although Lorentz symmetry has been tested at low energy with extremely good accuracy, its validity at very high energy is much less well established. If Lorentz symmetry violation (LSV) is energydependent (e.g. $\propto E^2$), it can be of order 1 at Planck scale and undetectable at GeV scale or below. Similarly, superluminal particles with positive mass and energy (superbradyons) can exist and be the ultimate building blocks of matter. We discuss a few cosmological consequences of such a scenario, as well as possible experimental tests.Is Part Of 19971231 Identifier ISSN: DOI 10.1142/9789814447263_0085Category physics.genphLicense 
arXivBalloonBorne Hard XRay Imaging and Future Surveys Jonathan E. Grindlay 19971231 Several payloads for hard Xray (20600 keV) imaging with coded aperture telescopes have been developed for balloon flight observations of cosmic xray sources. We briefly review the characteristics of these, particularly the EXITE2 system. The recent NASA program to develop an extended long duration (100d) balloon flight capability employing superpressure balloons would allow a qualitatively new hard xray imaging experiment: the Energetic Xray Imaging Survey TelescopeLong Integration Time Experiment (EXISTLITE). The longer continuous viewing times (per source) available from an LDB platform than from low earth orbit would enable both surveys and objectives complementary to the EXIST mission proposed for a MIDEX satellite. We summarize the scientific objectives of EXISTLITE, a possible instrumentation approach incorporating a large area array of CdZnTe (CZT) detectors, and our program for the development and balloon flight testing of relatively thick (5mm) CZT detector arrays.
Subject Source arXiv URL https://arxiv.org/abs/astroph/9712357view Article Title BalloonBorne Hard XRay Imaging and Future SurveysAuthors Jonathan E. GrindlayAbstract Several payloads for hard Xray (20600 keV) imaging with coded aperture telescopes have been developed for balloon flight observations of cosmic xray sources. We briefly review the characteristics of these, particularly the EXITE2 system. The recent NASA program to develop an extended long duration (100d) balloon flight capability employing superpressure balloons would allow a qualitatively new hard xray imaging experiment: the Energetic Xray Imaging Survey TelescopeLong Integration Time Experiment (EXISTLITE). The longer continuous viewing times (per source) available from an LDB platform than from low earth orbit would enable both surveys and objectives complementary to the EXIST mission proposed for a MIDEX satellite. We summarize the scientific objectives of EXISTLITE, a possible instrumentation approach incorporating a large area array of CdZnTe (CZT) detectors, and our program for the development and balloon flight testing of relatively thick (5mm) CZT detector arrays.Is Part Of 19971231 Identifier ISSN: DOI 10.1016/S02731177(97)010880Category astrophLicense 
arXivTolman's energy of a stringy charged black hole S. S. Xulu 19971231 Virbhadra and Parikh studied the energy distribution associated with stringy charged black hole in Einstein's prescription. We study the same using Tolman's energymomentum complex and get the same result as obtained by Virbhadra and Parikh. The entire energy is confined inside the black hole.
Subject Source arXiv URL https://arxiv.org/abs/grqc/9712100view Article Title Tolman's energy of a stringy charged black holeAuthors S. S. XuluAbstract Virbhadra and Parikh studied the energy distribution associated with stringy charged black hole in Einstein's prescription. We study the same using Tolman's energymomentum complex and get the same result as obtained by Virbhadra and Parikh. The entire energy is confined inside the black hole.Is Part Of Int.J.Theor.Phys.37:17731778,1998 19971231 Identifier ISSN: DOI 10.1023/A:1026600910525Category grqcLicense 
arXivLie symmetries of Einstein's vacuum equations in N dimensions Louis Marchildon 19971231 We investigate Lie symmetries of Einstein's vacuum equations in N dimensions, with a cosmological term. For this purpose, we first write down the second prolongation of the symmetry generating vector fields, and compute its action on Einstein's equations. Instead of setting to zero the coefficients of all independent partial derivatives (which involves a very complicated substitution of Einstein's equations), we set to zero the coefficients of derivatives that do not appear in Einstein's equations. This considerably constrains the coefficients of symmetry generating vector fields. Using the Lie algebra property of generators of symmetries and the fact that general coordinate transformations are symmetries of Einstein's equations, we are then able to obtain all the Lie symmetries. The method we have used can likely be applied to other types of equations.
Subject 수학 Source arXiv URL https://arxiv.org/abs/mathph/9801204view Article Title Lie symmetries of Einstein's vacuum equations in N dimensionsAuthors Louis MarchildonAbstract We investigate Lie symmetries of Einstein's vacuum equations in N dimensions, with a cosmological term. For this purpose, we first write down the second prolongation of the symmetry generating vector fields, and compute its action on Einstein's equations. Instead of setting to zero the coefficients of all independent partial derivatives (which involves a very complicated substitution of Einstein's equations), we set to zero the coefficients of derivatives that do not appear in Einstein's equations. This considerably constrains the coefficients of symmetry generating vector fields. Using the Lie algebra property of generators of symmetries and the fact that general coordinate transformations are symmetries of Einstein's equations, we are then able to obtain all the Lie symmetries. The method we have used can likely be applied to other types of equations.Is Part Of J. Nonlinear Math. Phys. 5 (1998), no. 1, 6881 19971231 Identifier ISSN: DOI 10.2991/jnmp.1998.5.1.7Category mathph math.MPLicense