6,227 research outputs found
Black hole hyperaccretion in collapsars. III. GRB timescale
Gamma-ray bursts (GRBs) are classified into long and short populations (i.e.,
LGRBs and SGRBs) based on the observed bimodal distribution of duration
. Multimessenger observations indicated that most SGRBs and LGRBs
should be powered by ultrarelativistic jets launched from black hole (BH)
hyperaccretion in compact object mergers and massive collapsars, respectively.
However, the duration criterion sometimes cannot correctly reflect the physical
origin of a particular GRB. In the collapsar scenario, a GRB can be observed
when the jet breaks out from the envelope and circumstellar medium
successfully. The observed GRB duration reflects only the time that the engine
operates after the jet breaks out. This work studies the propagation of jets
driven by the neutrino annihilation or Blandford-Znajek mechanism in massive
collapsars. The signatures of the progenitors for producing LGRBs, SGRBs, and
failed GRBs in the collapsar scenario are exhibited. The competition between
the mass supply onto the BH hyperaccretion and jet propagation into the
envelope are definitely dependent on the density profiles of the collapsars. We
show that duration and isotropic energy of GRBs can help
constrain the density profiles of collapsars. Finally, we propose that a
collapsar-origin SGRB, GRB 200826A, might originate from a
neutrino-annihilation-dominated jet launched by a collapsar
whose progenitor's envelope has been stripped.Comment: 9 pages, 4 figures, accepted for publication in Ap
Dynamic dissipative cooling of a mechanical oscillator in strong-coupling optomechanics
Cooling of mesoscopic mechanical resonators represents a primary concern in
cavity optomechanics. Here in the strong optomechanical coupling regime, we
propose to dynamically control the cavity dissipation, which is able to
significantly accelerate the cooling process while strongly suppressing the
heating noise. Furthermore, the dynamic control is capable of overcoming
quantum backaction and reducing the cooling limit by several orders of
magnitude. The dynamic dissipation control provides new insights for tailoring
the optomechanical interaction and offers the prospect of exploring macroscopic
quantum physics.Comment: accepetd in Physical Review Letter
Demonstration of Deutsch's Algorithm on a Stable Linear-Optical Quantum Computer
We report an experimental demonstration of quantum Deutsch's algorithm by
using linear-optical system. By employing photon's polarization and spatial
modes, we implement all balanced and constant functions for quantum computer.
The experimental system is very stable and the experimental data are excellent
in accordance with the theoretical results.Comment: 7 pages, 4 figure
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
Study on the Rheological Properties and Constitutive Model of Shenzhen Mucky Soft Soil
In order to obtain the basic parameters of numerical analysis about the time-space effect of the deformation occurring in Shenzhen deep soft-soil foundation pit, a series of triaxial consolidated-undrained shear rheology tests on the peripheral mucky soft soil of a deep foundation pit support were performed under different confining pressures. The relations between the axial strain of the soil and time, as well as between the pore-water pressure of the soil and time, were achieved, meanwhile on the basis of analyzing the rheological properties of the soil, the relevant rheological models were built. Analysis results were proved that the rheology of Shenzhen mucky soft soil was generally viscous, elastic, and plastic, and had a low yield stress between 90 and 150 kPa. The increase in pore-water pressure made the rheological time effect of the mucky soft soil more remarkable. Thus, the drainage performance in practical engineering should be improved to its maximum possibility extent to decrease the soft-soil rheological deformation. Lastly, a six-component extended Burgers model was employed to fit the test results and the parameters of the model were determined. Findings showed that the extended Burgers model could satisfactorily simulate the various rheological stages of the mucky soft soil. The constitutive model and the determination of its parameters can be served as a foundation for the time-space effect analysis on the deformation of deep soft-soil foundation pits
- âŚ