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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
Stability And Mechanical Properties Of W1-X Mox B4.2 (X=0.0-1.0) From First Principles, Weiguang Gong, Rui Xu, Xuecheng Shao, Quan Li, Changfeng Chen
Stability And Mechanical Properties Of W1-X Mox B4.2 (X=0.0-1.0) From First Principles, Weiguang Gong, Rui Xu, Xuecheng Shao, Quan Li, Changfeng Chen
Physics & Astronomy Faculty Research
Heavy transition-metal tetraborides (e.g., tungsten tetraboride, molybdenum tetraboride, and molybdenum-doped tungsten tetraboride) exhibit superior mechanical properties, but solving their complex crystal structures has been a long-standing challenge. Recent experimental x-ray and neutron diffraction measurements combined with first-principles structural searches have identified a complex structure model for tungsten tetraboride that contains a boron trimer as an unusual structural unit with a stoichiometry of 1:4.2. In this paper, we expand the study to binary MoB4.2 and ternary W1-xMoxB4.2 (x=0.0-1.0) compounds to assess their thermodynamic stability and mechanical properties using a tailor-designed crystal structure search method in conjunction with first-principles energetic calculations. Our …
Eccentric Neutron Star Disk Driven Type Ii Outburst Pairs In Be/X-Ray Binaries, Alessia Franchini, Rebecca G. Martin
Eccentric Neutron Star Disk Driven Type Ii Outburst Pairs In Be/X-Ray Binaries, Alessia Franchini, Rebecca G. Martin
Physics & Astronomy Faculty Research
Be star X-ray binaries are transient systems that show two different types of outbursts. Type I outbursts occur each orbital period while type II outbursts have a period and duration that are not related to any periodicity of the binary system. Type II outbursts may be caused by mass transfer to the neutron star from a highly eccentric Be star disk. A sufficiently misaligned Be star decretion disk undergoes secular Von Zeipel-Lidov-Kozai (ZLK) oscillations of eccentricity and inclination. Observations show that in some systems the type II outbursts come in pairs with the second being of lower luminosity. We use …
Nonperiodic Type I Be/X-Ray Binary Outbursts, Rebecca G. Martin, Alessia Franchini
Nonperiodic Type I Be/X-Ray Binary Outbursts, Rebecca G. Martin, Alessia Franchini
Physics & Astronomy Faculty Research
Type I Be/X-ray binary outbursts are driven by mass transfer from a Be star decretion disk to a neutron star companion during each orbital period. Treiber et al. recently observed nonperiodic type I outbursts in RX J0529.8-6556 that has unknown binary orbital properties. We show that nonperiodic type I outbursts may be temporarily driven in a low eccentricity binary with a disk that is inclined sufficiently to be mildly unstable to Kozai-Lidov oscillations. The inclined disk becomes eccentric and material is transferred to the neutron star at up to three locations in each orbit: when the neutron star passes the …
Global 3d Radiation Hydrodynamic Simulations Of Proto-Jupiter’S Convective Envelope, Zhaohuan Zhu, Yan-Fei Jiang, Hans Baehr, Andrew N. Youdin, Philip J. Armitage, Rebecca G. Martin
Global 3d Radiation Hydrodynamic Simulations Of Proto-Jupiter’S Convective Envelope, Zhaohuan Zhu, Yan-Fei Jiang, Hans Baehr, Andrew N. Youdin, Philip J. Armitage, Rebecca G. Martin
Physics & Astronomy Faculty Research
The core accretion model of giant planet formation has been challenged by the discovery of recycling flows between the planetary envelope and the disc that can slow or stall envelope accretion. We carry out 3D radiation hydrodynamic simulations with an updated opacity compilation to model the proto-Jupiter’s envelope. To isolate the 3D effects of convection and recycling, we simulate both isolated spherical envelopes and envelopes embedded in discs. The envelopes are heated at given rates to achieve steady states, enabling comparisons with 1D models. We vary envelope properties to obtain both radiative and convective solutions. Using a passive scalar, we …
Gw Ori: Circumtriple Rings And Planets, Jeremy L. Smallwood, Rebecca Nealon, Cheng Chen, Rebecca G. Martin, Jiaqing Bi, Ruobing Dong, Christophe Pinte
Gw Ori: Circumtriple Rings And Planets, Jeremy L. Smallwood, Rebecca Nealon, Cheng Chen, Rebecca G. Martin, Jiaqing Bi, Ruobing Dong, Christophe Pinte
Physics & Astronomy Faculty Research
GW Ori is a hierarchical triple star system with a misaligned circumtriple protoplanetary disc. Recent Atacama Large Millimeter/submillimeter Array observations have identified three dust rings with a prominent gap at 100 au and misalignments between each of the rings. A break in the gas disc may be driven by the torque from either the triple star system or a planet that is massive enough to carve a gap in the disc. Once the disc is broken, the rings nodally precess on different time-scales and become misaligned. We investigate the origins of the dust rings by means of N-body integrations and …
Terrestrial Planet Formation In A Circumbinary Disc Around A Coplanar Binary, Anna C. Childs, Rebecca G. Martin
Terrestrial Planet Formation In A Circumbinary Disc Around A Coplanar Binary, Anna C. Childs, Rebecca G. Martin
Physics & Astronomy Faculty Research
With N-body simulations, we model terrestrial circumbinary planet (CBP) formation with an initial surface density profile motivated by hydrodynamic circumbinary gas disc simulations. The binary plays an important role in shaping the initial distribution of bodies. After the gas disc has dissipated, the torque from the binary speeds up the planet formation process by promoting body-body interactions but also drives the ejection of planet building material from the system at an early time. Fewer but more massive planets form around a close binary compared to a single star system. A sufficiently wide or eccentric binary can prohibit terrestrial planet formation. …
The Large Area Burst Polarimeter (Leap) A Nasa Mission Of Opportunity For The Iss, Bing Zhang, Numerous Authors, See Full List Below
The Large Area Burst Polarimeter (Leap) A Nasa Mission Of Opportunity For The Iss, Bing Zhang, Numerous Authors, See Full List Below
Physics & Astronomy Faculty Research
The LargE Area Burst Polarimeter (LEAP) will radically improve our understanding of some of the most energetic phenomena in our Universe by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects. LEAP will do this by making the highest fidelity polarization measurements to date of the prompt gamma-ray emission from a large sample of Gamma-Ray Bursts (GRBs). The science objectives are met with a single instrument deployed as an external payload on the ISS-a wide FOV Compton polarimeter that measures GRB polarization from 50-500 keV and GRB spectra from ∼10 keV to 5 …
Free-Free Absorption In Hot Relativistic Flows: Application To Fast Radio Bursts, Esha Kundu, Bing Zhang
Free-Free Absorption In Hot Relativistic Flows: Application To Fast Radio Bursts, Esha Kundu, Bing Zhang
Physics & Astronomy Faculty Research
Magnetic flares create hot relativistic shocks outside the light cylinder radius of a magnetized star. Radio emission produced in such a shock or at a radius smaller than the shock undergoes free–free absorption while passing through the shocked medium. In this work, we demonstrate that this free–free absorption can lead to a negative drift in the frequency-time spectra. Whether it is related to the downward drift pattern observed in fast radio bursts (FRBs) is unclear. However, if the FRB down-drifting is due to this mechanism then it will be pronounced in those shocks that have isotropic kinetic energies ≳1044 erg. …
A Mechanical Model For Magnetized Relativistic Blastwaves, Shunke Ai, Bing Zhang
A Mechanical Model For Magnetized Relativistic Blastwaves, Shunke Ai, Bing Zhang
Physics & Astronomy Faculty Research
The evolution of a relativistic blastwave is usually delineated under the assumption of pressure balance between forward- and reverse-shocked regions. However, such a treatment usually violates the energy conservation law, and is inconsistent with existing magnetohydrodynamic numerical simulation results. A mechanical model of non-magnetized blastwaves was proposed in previous work to solve the problem. In this paper, we generalize the mechanical model to the case of a blastwave driven by an ejecta with an arbitrary magnetization parameter $\sigma_{\rm ej}$. We test our modified mechanical model by considering a long-lasting magnetized ejecta and found that it is much better than the …
Experimental Constraint On Axionlike Particles Over Seven Orders Of Magnitude In Mass, Tanya S. Roussy, Daniel A. Palken, William B. Cairncross, Benjamin M. Brubaker, Daniel N. Gresh, Matt Grau, Kevin C. Cossel, Kia Boon Ng, Yuval Shagam, Yan Zhou, Victor V. Flambaum, Konrad W. Lehnert, Jun Ye, Eric A. Cornell
Experimental Constraint On Axionlike Particles Over Seven Orders Of Magnitude In Mass, Tanya S. Roussy, Daniel A. Palken, William B. Cairncross, Benjamin M. Brubaker, Daniel N. Gresh, Matt Grau, Kevin C. Cossel, Kia Boon Ng, Yuval Shagam, Yan Zhou, Victor V. Flambaum, Konrad W. Lehnert, Jun Ye, Eric A. Cornell
Physics & Astronomy Faculty Research
We use our recent electric dipole moment (EDM) measurement data to constrain the possibility that the HfF+ EDM oscillates in time due to interactions with candidate dark matter axionlike particles (ALPs). We employ a Bayesian analysis method which accounts for both the look-elsewhere effect and the uncertainties associated with stochastic density fluctuations in the ALP field. We find no evidence of an oscillating EDM over a range spanning from 27 nHz to 400 mHz, and we use this result to constrain the ALP-gluon coupling over the mass range 10-22-10-15 eV. This is the first laboratory constraint on the ALP-gluon coupling …
On The Role Of Resonances In Polluting White Dwarfs By Asteroids, Jeremy L. Smallwood, Rebecca G. Martin, Mario Livio, Dimitri Veras
On The Role Of Resonances In Polluting White Dwarfs By Asteroids, Jeremy L. Smallwood, Rebecca G. Martin, Mario Livio, Dimitri Veras
Physics & Astronomy Faculty Research
Pollution of white dwarf atmospheres may be caused by asteroids that originate from the locations of secular and mean-motion resonances in planetary systems. Asteroids in these locations experience increased eccentricity, leading to tidal disruption by the white dwarf. We examine how the ν6 secular resonance shifts outwards into a previously stable region of the asteroid belt, as the star evolves to a white dwarf. Analytic secular models require a planet to be engulfed in order to shift the resonance. We show with numerical simulations that as a planet gets engulfed by the evolving star, the secular resonance shifts and the …
The Pencil Code, A Modular Mpi Code For Partial Differential Equations And Particles: Multipurpose And Multiuser-Maintained, The Pencil Code Collaboration, Chao-Chin Yang
The Pencil Code, A Modular Mpi Code For Partial Differential Equations And Particles: Multipurpose And Multiuser-Maintained, The Pencil Code Collaboration, Chao-Chin Yang
Physics & Astronomy Faculty Research
The Pencil Code is a highly modular physics-oriented simulation code that can be adapted to a wide range of applications. It is primarily designed to solve partial differential equations (PDEs) of compressible hydrodynamics and has lots of add-ons ranging from astrophysical magnetohydrodynamics (MHD) (A. Brandenburg & Dobler, 2010) to meteorological cloud microphysics (Li et al., 2017) and engineering applications in combustion (Babkovskaia et al., 2011). Nevertheless, the framework is general and can also be applied to situations not related to hydrodynamics or even PDEs, for example when just the message passing interface or input/output strategies of the code are to …
Constraining Protoplanetary Disc Accretion And Young Planets Using Alma Kinematic Observations, Ian Rabago, Zhaohuan Zhu
Constraining Protoplanetary Disc Accretion And Young Planets Using Alma Kinematic Observations, Ian Rabago, Zhaohuan Zhu
Physics & Astronomy Faculty Research
Recent ALMA molecular line observations have revealed 3D gas velocity structure in protoplanetary discs, shedding light on mechanisms of disc accretion and structure formation. (1) By carrying out viscous simulations, we confirm that the disc's velocity structure differs dramatically using vertical stress profiles from different accretion mechanisms. Thus, kinematic observations tracing flows at different disc heights can potentially distinguish different accretion mechanisms. On the other hand, the disc surface density evolution is mostly determined by the vertically integrated stress. The sharp disc outer edge constrained by recent kinematic observations can be caused by a radially varying alpha in the disc. …
Kozai–Lidov Oscillations Triggered By A Tilt Instability Of Detached Circumplanetary Discs, Rebecca G. Martin, Zhaohuan Zhu, Philip J. Armitage, Chao-Chin Yang, Hans Baehr
Kozai–Lidov Oscillations Triggered By A Tilt Instability Of Detached Circumplanetary Discs, Rebecca G. Martin, Zhaohuan Zhu, Philip J. Armitage, Chao-Chin Yang, Hans Baehr
Physics & Astronomy Faculty Research
Circumplanetary discs can be linearly unstable to the growth of disc tilt in the tidal potential of the star–planet system. We use 3D hydrodynamical simulations to characterize the disc conditions needed for instability, together with its long-term evolution. Tilt growth occurs for disc aspect ratios, evaluated near the disc outer edge, of H/r ≳ 0.05, with a weak dependence on viscosity in the wave-like regime of warp propagation. Lower mass giant planets are more likely to have circumplanetary discs that satisfy the conditions for instability. We show that the tilt instability can excite the inclination to above the threshold where …