[en] Electron correlation plays a crucial role in quantum many-body physics ranging from molecular bonding, strong-field–induced multi-electron ionization, to superconducting in materials. Understanding the dynamic electron correlation in the photoionization of relatively simple quantum three-body systems, such as He and He-like ions, is an important step toward manipulating complex systems through photo-induced processes. Here we have performed ab initio investigations of two-photon double ionization (TPDI) of He and He-like ions [Li⁺, Be²⁺, and C⁴⁺] exposed to intense attosecond x-ray pulses. Results from such fully correlated quantum calculations show weaker and weaker electron correlation effects in TPDI spectra as the ionic charge increases, which is counterintuitive to the belief that the strongly correlated ground state and the strong Coulomb field of He-like ions should lead to more equal-energy sharing in photoionization. Lastly, these findings indicate that the final-state electron–electron correlation ultimately determines their energy sharing in TPDI.

[en] Here, continuum lowering is a well-known and important physics concept that describes the ionization potential depression (IPD) in plasmas caused by thermal-/pressure-induced ionization of outer-shell electrons. The existing IPD models are often used to characterize plasma conditions and to gauge opacity calculations. Recent precision measurements have revealed deficits in our understanding of continuum lowering in dense hot plasmas. However, these investigations have so far been limited to IPD in strongly coupled but nondegenerate plasmas. Here, we report a first-principles study of the K-edge shifting in both strongly coupled and fully degenerate carbon plasmas, with quantum molecular dynamics (QMD) calculations based on the all-electron density-functional theory (DFT). The resulted K-edge shifting versus plasma density, as a probe to the continuum lowering and the Fermi-surface rising, is found to be significantly different from predictions of existing IPD models. In contrast, a simple model of “single atom in box” (SAIB), developed in this work, accurately predicts K-edge locations as what ab-initio calculations provide.

[en] Purpose: The retinoblastoma protein (pRB) is a key regulator of the G1 cell cycle checkpoint. Altered pRB expression has been documented in a significant percentage of muscle-invasive bladder cancers and has been associated with poorer overall survival. Since the relationship between pRB expression and radiation response is unknown, this was examined in patients treated between 1960 and 1983 with preoperative radiotherapy (50 Gy in 25 fractions) followed 4-6 weeks later by radical cystectomy. Materials and Methods: Immunohistochemical staining of pRB in paraffin-embedded tumor sections using WL-1 polyclonal anti-RB antibody was considered adequate in 98 of 100 pretreatment tumor samples. The overexpression of p53 by immunohistochemical staining using monoclonal antibody DO1 (n=97) and the apoptotic index (n=89) using morphologic criteria from hematoxylin and eosin stained slides were also quantified. In contrast to pRB, wherein a lack of pRB staining indicates altered expression, the presence of p53 staining is indicative of a putative p53 mutation. There were 46 patients in Stage T2, 28 in Stage T3a, and 24 in Stage T3b. The median age was 62 years and follow-up for those living was 85 months. Results: Staining for pRB was negative in 30% of the cases. Correlations were observed between pRB negativity and high pretreatment apoptosis level (p=0.06), more advanced clinical stage (p=0.01), increased clinical-to-pathologic downstaging (p=0.014), and more pathologic complete responses (Path-CRs; p=0.019). Several other factors were tested and none were associated with downstaging, including p53 expression or apoptotic index. Thus, RB status was the only pretreatment prognostic factor in the univariate analyses that correlated with downstaging. RB status was also independently related to Path-CR using multivariate logistic regression. Despite these significant relationships, no correlations between pRB staining and patient outcome were observed when the entire cohort was analyzed. Restriction of the analyses to Stage T3b patients, however, revealed that pRB negativity predicted for enhanced distant metastasis freedom (p=0.006, logrank) and overall survival (p=0.02). The only other significant predictors of distant metastasis for Stage T3b patients were p53 staining (p=0.02) and Path-CR (p=0.03), and for overall survival were p53 staining (p=0.003) and hemoglobin level (p=0.03). These data indicate that different mechanisms were responsible for the correlations of p53 and pRB status to distant metastasis and overall survival rates, since only pRB expression correlated with radiation response. To examine this further, the patients were divided into 4 groups based on p53 and pRB staining patterns. When this was done for the entire cohort, as well as for Stage T3b patients, superior distant metastasis freedom and overall survival rates were seen when there was no staining for either p53 or pRB. Hence altered pRB expression and wild-type p53 expression was associated with the best outcome, presumably because these attributes were complimentary. Conclusion: These data demonstrate that RB status measured by immunohistochemical staining is a strong correlate of radiation response, far beyond that of any other known prognostic factor. Because the loss of pRB function has been associated with a worse prognosis in other studies wherein radiotherapy was not used, it appears that this abnormality imparted enhanced radiosensitivity which counterbalanced the other related adverse characteristics. Moreover, the segregation of radiation response and patient outcome characteristics by the p53 and pRB immunohistochemical staining patterns suggests that these markers represent independent functional defects. pRB immunohistochemical staining status may be a useful marker for selecting patients for bladder preservation

[en] Through solving the three-dimensional (3D) time-dependent Schroedinger equation, we have investigated how an intense, circularly/elliptically-polarized, few-cycle pulse rotates the electronic wave packets of a dissociated diatomic molecule. When such rotating wave packets from one atomic core sweep quickly through the other nucleus, recombination occurs and generates a supercontinuum radiation spectrum. The numerical solution of the Maxwell equation for the 3D propagation of such supercontinuum radiation in realistic molecular gases has confirmed the generation of a single attosecond (as) pulse, with a duration of ∼186 as. Moreover, the proposed scheme can push the extreme ultraviolet (EUV) pulse generation down to the sub-100-attosecond regime. As an example, we have shown a single EUV pulse of ∼90 as, using an elliptical driving pulse. (letter to the editor)

[en] We have numerically investigated ionization of molecules exposed to circularly polarized (CP) intense few-cycle pulses (FCPs) by solving the three-dimensional time-dependent Schroedinger equation. The resulting photoelectron spectra exhibit an interesting ''plateau'' feature that does not appear for atoms exposed to circularly-polarized laser fields. The origin comes from the intense CP field ionizing a portion of the electron wave packet about one nuclear center and driving it through the other. Moreover, the angular distribution of photoelectrons gives an indication of the carrier-envelope phase of the applied FCP, which implies that steering of photoelectrons in space can be achieved by controlling the FCP phase

[en] Slow collisions of electrons with Rydberg sodium atoms have been quantum mechanically investigated by using the time-dependent close-coupling (TDCC) method. To make such large-scale calculations possible, it is essential to implement the TDCC method with the powerful finite-element discrete variable representation (FEDVR). Besides visualizing the slow collision dynamics, our quantum calculations show interesting features in the slow electron impact ionization of Rydberg atoms. The energy sharing between two continuum electrons changes dramatically as the incoming electron energy decreases. Predominant equal-energy sharing is observed in such a cold (e,2e) process, even though the impact electron energy is still twice the binding energy of the Rydberg electron

[en] Complete two-photon break-up of He near threshold has been investigated by solving the time-dependent closing-coupling equations on a numerical lattice. We have obtained good agreement for the total double ionization cross-section with previous theoretical results. The triple-differential cross-sections exhibit interesting features as the two-photon energy approaches the threshold of double ionization. We found that two-electron ejection with equal energy sharing is most probable near the two-photon threshold, in contrast to the case away from threshold, where ejection with large unequal energy sharings is most probable. (letter to the editor)

[en] By solving the three-dimensional, time-dependent Schroedinger equation, we have demonstrated that the ultrafast charge-transfer process in ion-atom collisions can be mapped out with attosecond extreme uv (xuv) pulses. During the dynamic-charge transfer from the target atom to the projectile ion, the electron coherently populates the two sites of both nuclei, which can be viewed as a 'short-lived' molecular state. A probing attosecond xuv pulse can instantly unleash the delocalized electron from such a ''transient molecule,'' so that the resulting photoelectron may exhibit a ''double-slit'' interference. On the contrary, either reduced or no photoelectron interference will occur if the attosecond xuv pulse strikes well before or after the collision. Therefore, by monitoring the photoelectron interference visibility, one can precisely time the ultrafast charge-transfer process in atomic collisions with time-delayed attosecond xuv pulses.

[en] The recent proposal to use highly charged ions as sources of electrons for laser acceleration [S. X. Hu and A. F. Starace, Phys. Rev. Lett. 88, 245003 (2002)] is investigated here in detail by means of three-dimensional, relativistic Monte Carlo simulations for a variety of system parameters, such as laser pulse duration, ionic charge state, and laser focusing spot size. Realistic laser focusing effects--e.g., the existence of longitudinal laser field components--are taken into account. Results of spatial averaging over the laser focus are also presented. These numerical simulations show that the proposed scheme for laser acceleration of electrons from highly charged ions is feasible with current or near-future experimental conditions and that electrons with GeV energies can be obtained in such experiments

[en] Molecular-dynamics simulations have been performed for frozen Rydberg gases in a strong magnetic field of B = 2.9 T, up to a microsecond time scale. We found that a small number of spontaneously ionized electrons may de-excite a large portion of Rydberg atoms, while the free electrons leave the frozen Rydberg gases along the B-field. Such de-excitations as well as Rydberg-Rydberg atom interactions can induce significant heating to strongly magnetized Rydberg gases. Kinetic energy increase by 2-3 orders of magnitude has been observed for the initially frozen (∼0.2 mK) Rydberg gases. (fast track communication)