Influence of autoionizing states on the pulse-length dependence of strong-field Ne+ photoionization at 38.4 eV

International audienceUsing the time-dependent R-matrix approach, we investigate ionization of ground-state Ne +, irradiated by laser light with a photon energy of 38.4 eV at intensities 10 13 W cm −2, 2 × 10 13 W cm −2 and 10 14 W cm −2 as a function of pulse length. Although the photon energy is below the threshold for single-photon ionization, we obtain a significant contribution from single-photon ionization to the ionization probability due to the finite duration of the pulse. The two-photon ionization rates deduced from the calculations are consistent with those obtained in R-matrix-Floquet rate calculations. The ionization probability oscillates with pulse length, which is ascribed to population and depopulation of autoionizing states just above the Ne 2+ ground state, reached after absorption of a single photon. At an intensity of 10 14 W cm −2, pulse lengths longer than 50 cycles are required for two-photon ionization to dominate the ionization probability. Letter to the Editor 2 The development of free-electron lasers operating in the VUV and the X-ray domain has given experimentalists new ways of investigating multi-electron dynamics in strong laser fields. These new laser facilities have, for example, enabled experimentalists to investigate two-photon double ionization of Ne in the photon-energy regime where direct two-photon double ionization is energetically allowed, but sequential (Ne → Ne + → Ne 2+) double ionization is energetically not allowed since the photon energy is not sufficient to ionize Ne + with a single photon (eg. Sorokin et al 2007). At larger photon energies, sequential double ionization is allowed, but also in this process one can find signatures of the fact that the two different emission processes are not independent of each other (Fritzsche et al 2008). One of the grand challenges in theoretical atomic physics is the description of multielectron dynamics in complex atoms irradiated by intense laser pulses. Over the last 15 years, great progress has been made in the description of pure two-electron systems in intense laser fields, for example for two-photon double ionization processes (see, for example, Colgan et al 2002, Feng and van der Hart 2003, Laulan et al 2005, Feist et al 2008) as well as for multiphoton double ionization at 390 nm (Parker et al 2006). These calculations require substantial computational resources, such that the direct extension of these techniques to systems with more than two electrons, like Ne, is unfeasible at present. Other approaches are required to describe the behaviour of complex atoms in intense light fields. The most successful approach for the description of complex atoms in intense laser light at present is the R-matrix-Floquet approach. This approach was designed from the outset to treat complex atoms in intense light fields by combining the R-matrix approach with the Floquet Ansatz (Burke et al 1991). It has been applied to a wide range of problems, ranging from strong-field ionization of Ne and Ar at 390 nm, requiring absorption of at least eight and six photons respectively, (van der Hart 2006) to twophoton emission of the inner 1s electron from ground-state Li − (van der Hart 2005). More recently, the R-matrix-Floquet approach has been instrumental in indicating the importance of detailed atomic structure in two-photon ionization of Ne + (Hamonou et al 2008, Hamonou and van der Hart 2008). The theoretical investigation of ionization processes in Ne + is of particular relevance at the moment, due to the large number of strong-field multiple ionization studies on Ne at photon energies in the range between 38 and 50 eV. Ionization yields of various Ne ions were obtained by Sorokin et al (2007) at photon energies below the Ne + ionization threshold and above this threshold. Moshammer et al (2007) obtained detailed recoil momentum spectra for two-photon double ionization of Ne at 44 eV. Rudenko et al (2008) found that these recoil-ion momentum distributions differed strongly from the recoil-ion momentum distributions for two-photon double ionization of He at 44 eV. At 44 eV, sequential double ionization is allowed for Ne, whereas it is not allowed for He. The dominance of sequential double ionization of Ne was demonstrated experimentally by Kurka et al (2009). Whereas in previous work (Hamonou et al 2008, Hamonou and van der Hart 2009)

Time delay between photoemission from the 2p and 2s subshells of Neon

The R-Matrix incorporating Time (RMT) method is a new method for solving the time-dependent Schroedinger equation for multi-electron atomic systems exposed to intense short-pulse laser light. We have employed the RMT method to investigate the time delay in the photoemission of an electron liberated from a 2p orbital in a neon atom with respect to one released from a 2s orbital following absorption of an attosecond XUV pulse. Time delays due to XUV pulses in the range 76-105 eV are presented. For an XUV pulse at the experimentally relevant 105.2 eV, we calculate the time delay to be 10.2 +/- 1.3 attoseconds, somewhat larger than estimated by other theoretical calculations, but still a factor two smaller than experiment. We repeated the calculation for a photon energy of 89.8 eV with a larger basis set capable of modelling correlated-electron dynamics within the neon atom and the residual Ne(+) ion. A time delay of 14.5 +/- 1.5 attoseconds was observed, compared to a 16.7 +/- 1.5 attosecond result using a single-configuration representation of the residual Ne(+) ion.Comment: 4 pages, 3 figures, 1 tabl

Using differential reinforcement of high rates of behavior to improve work productivity : a replication and extension

Background: Due to deficits in adaptive and cognitive functioning, productivity may pose challenges for individuals with intellectual disability in the workplace.Method: Using a changing‐criterion embedded in a multiple baseline across partici‐pants design, we examined the effects of differential reinforcement of high rates of behaviour (DRH) on the rate of data entry (i.e., productivity) in four adults with intel‐lectual disability.Results: Although the DRH procedure increased the rate of correct data entry in all four participants, none of the participants achieved the criterion that we set with novice undergraduate students.Conclusions: Our results indicate that DRH is an effective intervention to increase rate of correct responding in individuals with intellectual disability, but that achiev‐ing the same productivity as workers without disability may not always be possible

Identifying a Novel Role for Fractalkine (CX3CL1) in Memory CD8(+) T Cell Accumulation in the Omentum of Obesity-Associated Cancer Patients

The omentum is enriched with pro-inflammatory effector memory CD8+ T cells in patients with the obesity-associated malignancy, esophagogastric adenocarcinoma (EAC) and we have identified the chemokine macrophage inflammatory protein-1alpha as a key player in their active migration to this inflamed tissue. More recently, others have established that subsets of memory CD8+ T cells can be classified based on their surface expression of CX3CR1; the specific receptor for the inflammatory chemokine fractalkine. CD8+ T cells expressing intermediate levels (CX3CR1INT) are defined as peripheral memory, those expressing the highest levels (CX3CR1HI) are effector memory/terminally differentiated and those lacking CX3CR1 (CX3CR1NEG) are classified as central memory. To date, the fractalkine:CX3CR1 axis has not been examined in the context of CD8+ T cell enrichment in the omentum and here we examine this chemokines involvement in the accumulation of memory CD8+ T cells in the omentum of EAC patients. Our data show that fractalkine is significantly enriched in the omentum of EAC patients and drives migration of T cells derived from EAC patient blood. Furthermore, CX3CR1 is endocytosed specifically by CD8+ T cells upon encountering fractalkine, which is consistent with the significantly diminished frequencies of CX3CR1INT and CX3CR1HI CD8+ T cells in the fractalkine-rich environment of omentum in EAC, relative to matched blood. Fractalkine-mediated endocytosis of CX3CR1 by CD8+ T cells is sustained and is followed by enhanced surface expression of L-selectin (CD62L). These novel data align with our findings that circulating CX3CR1NEG CD8+ T cells express higher levels of L-selectin than CX3CR1INT CD8+ T cells. This is consistent with previous reports and implicates fractalkine in the conversion of CX3CR1INT CD8+ T cells to a CX3CR1NEG phenotype characterized by alterations in the migratory capacity of these T cells. For the first time, these findings identify fractalkine as a driver of T cell migration to the omentum in EAC and indicate that CD8+ T cells undergo sequenced fractalkine-mediated alterations in CX3CR1 and L-selectin expression. These data implicate fractalkine as more than a chemotactic cytokine in obesity-associated meta-inflammation and reveal a role for this chemokine in the maintenance of the CX3CR1NEG CD8+ T cell populations

Clinical Application of Computer-Aided Diagnostic System for Harmonious Introduction of Complementary Dialysis Therapy

In chronic peritoneal dialysis (PD) therapy, peritoneal permeability is gradually enhanced over the duration of the therapeutic course, leading to a grave decline in the therapeutic efficiency. In recent years, a novel therapy (CD therapy), which integrates PD therapy with hemodialysis therapy, is being applied to end-stage PD patients to complement the decline of therapeutic efficiency caused by the grave degeneration of the peritoneal tissue. To realize a harmonious introduction of the CD therapy, this study developed a useful index (KAu/c), which evaluates both therapeutic efficiency and degeneration of peritoneal tissue. Using a mathematical model and KAu/c, we were able to validate the therapeutic efficiency in the PD patients, and, in one case, propose a better prescription for the patient by employing the CD therapy. The clinical implementation of this methodology is indispensable with regard to expanding the therapeutic monitoring system for renal replacement therapy

Energy extraction from the biologic battery in the inner ear

Endocochlear potential (EP) is a battery-like electrochemical gradient found in and actively maintained by the inner ear [superscript 1, 2]. Here we demonstrate that the mammalian EP can be used as a power source for electronic devices. We achieved this by designing an anatomically sized, ultra-low quiescent-power energy harvester chip integrated with a wireless sensor capable of monitoring the EP itself. Although other forms of in vivo energy harvesting have been described in lower organisms [superscript 3, 4, 5], and thermoelectric [superscript 6], piezoelectric [superscript 7] and biofuel [superscript 8, 9] devices are promising for mammalian applications, there have been few, if any, in vivo demonstrations in the vicinity of the ear, eye and brain. In this work, the chip extracted a minimum of 1.12 nW from the EP of a guinea pig for up to 5 h, enabling a 2.4 GHz radio to transmit measurement of the EP every 40–360 s. With future optimization of electrode design, we envision using the biologic battery in the inner ear to power chemical and molecular sensors, or drug-delivery actuators for diagnosis and therapy of hearing loss and other disorders.Focus Center Research Program. Focus Center for Circuit & System Solutions. Semiconductor Research Corporation. Interconnect Focus CenterNational Institutes of Health (U.S.) (Grant K08 DC010419)National Institutes of Health (U.S.) (Grant T32 DC00038)Bertarelli Foundatio