2,879 research outputs found
Laser-induced nonsequential double ionization at and above the recollision-excitation-tunneling threshold
We perform a detailed analysis of the recollision-excitation-tunneling (RESI)
mechanism in laser-induced nonsequential double ionization (NSDI), in which the
first electron, upon return, promotes a second electron to an excited state,
from which it subsequently tunnels, based on the strong-field approximation. We
show that the shapes of the electron momentum distributions carry information
about the bound-state with which the first electron collides, the bound state
to which the second electron is excited, and the type of electron-electron
interaction. Furthermore, one may define a driving-field intensity threshold
for the RESI physical mechanism. At the threshold, the kinetic energy of the
first electron, upon return, is just sufficient to excite the second electron.
We compute the distributions for helium and argon in the threshold and
above-threshold intensity regime. In the latter case, we relate our findings to
existing experiments. The electron-momentum distributions encountered are
symmetric with respect to all quadrants of the plane spanned by the momentum
components parallel to the laser-field polarization, instead of concentrating
on only the second and fourth quadrants.Comment: 14 pages, 7 figure
Automated Grain Yield Behavior Classification
A method for classifying grain stress evolution behaviors using unsupervised learning techniques is presented. The method is applied to analyze grain stress histories measured in-situ using high-energy X-ray diffraction microscopy (HEDM) from the aluminum-lithium alloy Al-Li 2099 at the elastic-plastic transition (yield). The unsupervised learning process automatically classified the grain stress histories into four groups: major softening, no work-hardening or softening, moderate work-hardening, and major work-hardening. The orientation and spatial dependence of these four groups are discussed. In addition, the generality of the classification process to other samples is explored
A PERFECT STORM: THE ETHICAL CHALLENGES OF SIMULTANEOUS INCREASES IN THE NEED FOR LONG-TERM CARE, USE OF DIRECT-TO-CONSUMER GENETIC TESTING, AND RISK OF GENETIC DISCRIMINATION IN THE U.S.
The phrase ‘a perfect storm’ is an expression first derived from the novel The Perfect Storm by Sebastian Junger, meaning three concurrent circumstances colliding to create a poor outcome. The United States is approaching a current day Perfect Storm between the healthcare, healthcare technology, and legislative spaces. This paper begins with a case study to ground the discussion before diving into the Perfect Storm’s three elements; an increased demand for long-term care due to the rapidly aging population and increased life expectancy, an increased use of direct-to-consumer (DTC) genetic testing used for determining genetic risk of disease, and an increased risk of genetic discrimination and lack of adequate legislative protections. Ethical and moral principles will be connected to the Perfect Storm showing how many identified ethical aspects are, or will be, in violation of principles as these three factors continue to converge. This paper is not meant to outline a solution to the Perfect Storm, but suggestions for ways to think about alleviating burdens from these elements will be discussed. The United States is reaching a critical breaking point where these three factors are set to have serious consequences if appropriate actions are not taken
Time-delayed nonsequential double ionization with few-cycle laser pulses: importance of the carrier-envelope phase
We perform theoretical investigations of laser-induced nonsequential double
ionization with few cycle pulses, with particular emphasis on the dependence of
the electron-momentum distributions on the carrier-envelope phase. We focus on
the recollision-excitation with subsequent tunneling ionization (RESI) pathway,
in which a released electron, upon return to its parent ion, gives part of its
kinetic energy to promote a second electron to an excited state. At a
subsequent time, the second electron is freed through tunneling ionization. We
show that the RESI electron-momentum distributions vary dramatically with
regard to the carrier-envelope phase. By performing a detailed analysis of the
dynamics of the two active electrons in terms of quantum orbits, we relate the
shapes and the momentum regions populated by such distributions to the dominant
set of orbits along which rescattering of the first electron and ionization of
the second electron occurs. These orbits can be manipulated by varying the
carrier-envelope phase. This opens a wide range of possibilities for
controlling correlated attosecond electron emission by an adequate pulse
choice.Comment: 12 pages, 7 figures, 1 tabl
Primary and secondary scintillation measurements in a xenon Gas Proportional Scintillation Counter
NEXT is a new experiment to search for neutrinoless double beta decay using a
100 kg radio-pure high-pressure gaseous xenon TPC. The detector requires
excellent energy resolution, which can be achieved in a Xe TPC with
electroluminescence readout. Hamamatsu R8520-06SEL photomultipliers are good
candidates for the scintillation readout. The performance of this
photomultiplier, used as VUV photosensor in a gas proportional scintillation
counter, was investigated. Initial results for the detection of primary and
secondary scintillation produced as a result of the interaction of 5.9 keV
X-rays in gaseous xenon, at room temperature and at pressures up to 3 bar, are
presented. An energy resolution of 8.0% was obtained for secondary
scintillation produced by 5.9 keV X-rays. No significant variation of the
primary scintillation was observed for different pressures (1, 2 and 3 bar) and
for electric fields up to 0.8 V cm-1 torr-1 in the drift region, demonstrating
negligible recombination luminescence. A primary scintillation yield of 81 \pm
7 photons was obtained for 5.9 keV X-rays, corresponding to a mean energy of 72
\pm 6 eV to produce a primary scintillation photon in xenon.Comment: 16 pages, 10 figures, accepted for publication in JINS
Nordic collaboration on the use of mass-spectrometers for the analysis of radioisotopes. NKS-project NORCMASS. Final report
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