62,965 research outputs found
Probing dipole-forbidden autoionizing states by isolated attosecond pulses
We propose a general technique to retrieve the information of
dipole-forbidden resonances in the autoionizing region. In the simulation, a
helium atom is pumped by an isolated attosecond pulse in the extreme
ultraviolet (EUV) combined with a few-femtosecond laser pulse. The excited wave
packet consists of the , , and states, including the background
continua, near the doubly excited state. The resultant electron
spectra with various laser intensities and time delays between the EUV and
laser pulses are obtained by a multilevel model and an ab initio time-dependent
Schr\"odinger equation calculation. By taking the ab initio calculation as a
"virtual measurement", the dipole-forbidden resonances are characterized by the
multilevel model. We found that in contrast to the common assumption, the
nonresonant coupling between the continua plays a significant role in the
time-delayed electron spectra, which shows the correlation effect between
photoelectrons before they leave the core. This technique takes the advantages
of ultrashort pulses uniquely and would be a timely test for the current
attosecond technology.Comment: 10 pages, 6 figure
Adaptive just-in-time code diversification
We present a method to regenerate diversified code dynamically in a Java bytecode JIT compiler, and to update the diversification frequently during the execution of the program. This way, we can significantly reduce the time frame in which attackers can let a program leak useful address space information and subsequently use the leaked information in memory exploits. A proof of concept implementation is evaluated, showing that even though code is recompiled frequently, we can achieved smaller overheads than the previous state of the art, which generated diversity only once during the whole execution of a program
Flavor-twisted boundary condition for simulations of quantum many-body systems
We present an approximative simulation method for quantum many-body systems
based on coarse graining the space of the momentum transferred between
interacting particles, which leads to effective Hamiltonians of reduced size
with the flavor-twisted boundary condition. A rapid, accurate, and fast
convergent computation of the ground-state energy is demonstrated on the
spin-1/2 quantum antiferromagnet of any dimension by employing only two sites.
The method is expected to be useful for future simulations and quick estimates
on other strongly correlated systems.Comment: 6 pages, 2 figure
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