A short note on the presence of spurious states in finite basis approximations

The genesis of spurious solutions in finite basis approximations to operators which possess a continuum and a point spectrum is discussed and a simple solution for identifying these solutions is suggested

Augmented collisional ionization via excited states in XUV cluster interactions

The impact of atomic excited states is investigated via a detailed model of laser-cluster interactions, which is applied to rare gas clusters in intense femtosecond pulses in the extreme ultraviolet (XUV). This demonstrates the potential for a two-step ionization process in laser-cluster interactions, with the resulting intermediate excited states allowing for the creation of high charge states and the rapid dissemination of laser pulse energy. The consequences of this excitation mechanism are demonstrated through simulations of recent experiments in argon clusters interacting with XUV radiation, in which this two-step process is shown to play a primary role; this is consistent with our hypothesis that XUV-cluster interactions provide a unique window into the role of excited atomic states due to the relative lack of photoionization and laser field-driven phenomena. Our analysis suggests that atomic excited states may play an important role in interactions of intense radiation with materials in a variety of wavelength regimes, including potential implications for proposed studies of single molecule imaging with intense X-rays.Comment: 4 pages, 2 figure

Molecular dynamics simulations of an engineered T4 lysozyme exclude helix to sheet transition, and provide insights into long distance, intra-protein switchable motion

An engineered variant of T4 lysozyme serves as a model for studying induced remote conformational changes in a full protein context. The design involves a duplicated surface helix, flanked by two loops, that switches between two different conformations spanning about 20 Å. Molecular dynamics simulations of the engineered protein, up to 1 μs, rule out α-helix to β-sheet transitions within the duplicated helix as suggested by others. These simulations highlight how the use of different force fields can lead to radical differences in the structure of the protein. In addition, Markov state modeling and transition path theory were employed to map a 6.6 μs simulation for possible early intermediate states and to provide insights into the onset of the switching motion. The putative intermediates involve the folding of one helical turn in the C-terminal loop through energy driven, sequential rearrangement of nearby salt bridges around the key residue Arg63. These results provide a first step towards understanding the energetics and dynamics of a rather complicated intra-protein motion

Pilot, randomized study assessing safety, tolerability and efficacy of simplified LPV/r maintenance therapy in HIV patients on the 1 st PI-based regimen

Objectives: To compare the efficacy and safety of an individualized treatment-simplification strategy consisting of switching from a highly-active anti-retroviral treatment (HAART) with a ritonavir-boosted protease inhibitor (PI/r) and 2 nucleoside reverse-transcriptase inhibitors (NRTIs) to lopinavir/ritonavir (LPV/r) monotherapy, with intensification by 2 NRTIs if necessary, to that of continuing their HAART. Methods: This is a one-year, randomized, open-label, multi-center study in virologically-suppressed HIV-1-infected adults on their first PI/r-containing treatment, randomized to either LPV/r-monotherapy or continue their current treatment. Treatment efficacy was determined by plasma HIV-1 RNA viral load (VL), time-to-virologic rebound, patient-reported outcomes (PROs) and CD4+T-cell-count changes. Safety was assessed with the incidence of treatment-emergent adverse events (AE). Results: Forty-one patients were randomized to LPV/r and 39 to continue their HAART. No statistically-significant differences between the two study groups in demographics and baseline characteristics were observed. At day-360, 71(39:LPV/r;32:HAART) patients completed treatment, while 9(2:LPV/r;7:HAART) discontinued. In a Last Observation Carried Forward Intent-to-Treat analysis, 40(98%) patients on LPV/r and 37(95%) on HAART had VL<200copies/mL (P = 0.61). Time-to-virologic rebound, changes in PROs, CD4+ T-cell-count and VL from baseline, also exhibited no statistically-significant between-group differences. Most frequent AEs were diarrhea (19%), headache (18%) and influenza (16%). Four (10%) patients on LPV/r were intensified with 2 NRTIs, all regaining virologic control. Eight serious AEs were reported by 5(2:LPV/r;3:HAART) patients. Conclusion: At day-360, virologic efficacy and safety of LPV/r appears comparable to that of a PI+2NRTIs HAART. These results suggest that our individualized, simplified maintenance strategy with LPV/r-monotherapy and protocol-mandated NRTI re-introduction upon viral rebound, in virologically-suppressed patients merits further prospective long-term evaluation. Trial Registration: ClinicalTrials.gov NCT00159224. © 2011 Cahn et al

Ionization dynamics of XUV excited clusters: the role of inelastic electron collisions

We report on the ionization and nanoplasma dynamics of small xenon clusters irradiated by intense, short pulses of a short-wavelength free-electron laser. Fluorescence spectroscopy indicates that inelastic electron collisions play a prominent role in the formation of the highest charge states. From the spectral distribution an electron temperature of 27 eV is deduced which corresponds to the average excess energy of the Auger- and photoelectrons ionized from individual atoms but trapped in the cluster core. This suggests that fluorescence spectra reflect a very early stage within the nanoplasma dynamics and shows how a part of the kinetic energy of the plasma electrons trapped in the cluster potential is transferred to the ions.ISSN:1361-6455ISSN:0368-3508ISSN:0953-4075ISSN:0022-370