Photodissociation of Non-Covalent Peptide-Crown Ether Complexes

Highly chromogenic 18-crown-6-dipyrrolylquinoxaline coordinates primary amines of peptides, forming non-covalent complexes that can be transferred to the gas-phase by electrospray ionization. The appended chromogenic crown ether facilitates efficient energy transfer to the peptide upon ultraviolet irradiation in the gas phase, resulting in diagnostic peptide fragmentation. Collisional-activated dissociation and infrared multiphoton dissociation of these non-covalent complexes result only in their disassembly with the charge retained on either the peptide or crown ether, yielding no sequence ions. Upon UV photon absorption the intermolecular energy transfer is facilitated by the fast activation timescale of ultraviolet photodissociation (<10 ns) and by the collectively strong hydrogen bonding between the crown ether and peptide, thus allowing effective transfer of energy to the peptide moiety before disruption of the intermolecular hydrogen bonds

Validation of the cognitive recovery assessments with the Postoperative Quality of Recovery Scale in patients with low-baseline cognition

Patients with pre-surgery cognitive impairment cannot currently be assessed for cognitive recovery after surgery using the Postoperative Quality of Recovery Scale (PostopQRS),as they would mathematically be scored as recovered. The group nonetheless represent a frail cohort at high risk of recovering poorly. We aimed to validate a novel method to score cognitive recovery in patients with low baseline cognition, using the number of low-score tests rather than their numerical values. Face validity was demonstrated in 86 participants in whom both PostopQRS and an 11-item neuropsychological battery were performed. The PostopQRS agreed with neuropsychological categorization of low versus normal cognition 74% of the time, with all but 5 incorrectly coded participants deviating by only 1 neurocognitive test. Cognitive recovery over time was comparable for groups with differing baseline cognitive function, irrespective of whether PostopQRS or neuropsychological methods were used. Discriminant validation was demonstrated in a post hoc analysis of the Steroids in Cardiac Surgery (SIRS) substudy by allocating groups to normal (n=246) or low baseline cognition (n=231) stratified by cognitive recovery on day 1. Recovery was similar for participants with low and normal baseline cognition. Postoperative length of stay was longer in patients with failed cognitive recovery whether they had normal (10.4±10.0 vs. 8.0±5.9 days, P=0.02) or low baseline cognition (12.0±11.1 vs. 8.2±4.7 days, P<0.01). Overall quality of recovery, as well as cognitive, emotive, and physiological recovery in those who recovered was independent of baseline cognition. The modified scoring method for the PostopQRS cognitive domain therefore demonstrates acceptable face and discriminant validity

Ondansetron does not reduce the shivering threshold in healthy volunteers

Background. Ondansetron, a serotonin-3 receptor antagonist, reduces postoperative shivering. Drugs that reduce shivering usually impair central thermoregulatory control, and may thus be useful for preventing shivering during induction of therapeutic hypothermia. We determined, therefore, whether ondansetron reduces the major autonomic thermoregulatory response thresholds (triggering core temperatures) in humans. Methods. Control (placebo) and ondansetron infusions at the target plasma concentration of 250 ng ml−1 were studied in healthy volunteers on two different days. Each day, skin and core temperatures were increased to provoke sweating; then reduced to elicit peripheral vasoconstriction and shivering. We determined the core-temperature sweating, vasoconstriction and shivering thresholds after compensating for changes in mean-skin temperature. Data were analysed using t-tests and presented as means (sds); P<0.05 was taken as significant. Results. Ondensetron plasma concentrations were 278 (57), 234 (55) and 243 (58) ng ml−1 at the sweating, vasoconstriction and shivering thresholds, respectively; these corresponded to ≈50 mg of ondansetron which is approximately 10 times the dose used for postoperative nausea and vomiting. Ondansetron did not change the sweating (control 37.4 (0.4)°C, ondansetron 37.6 (0.3)°C, P=0.16), vasoconstriction (37.0 (0.5)°C vs 37.1 (0.3)°C; P=0.70), or shivering threshold (36.3 (0.5)°C vs 36.3 (0.6)°C; P=0.76). No sedation was observed on either study day. Conclusions. Ondansetron appears to have little potential for facilitating induction of therapeutic hypothermi

Damping of the Transverse Head-Tail Instability by Periodic Modulation of the Chromaticity

An analytical and numerical study of the suppression of the transverse head-tail instability by modulating the chromaticity over a synchrotron period is presented. We find that a threshold can be developed, and it can be increased to a value larger than the strong head-tail instability threshold. The stability criterion derived agrees very well with the simulations. The underlying physical mechanisms of the damping scheme are rotation of the head-tail phase such that the instability does not occur, and Landau damping due to the incoherent betatron tune spread generated by the varying chromaticity. {copyright} {ital 1997} {ital The American Physical Society

Varying chromaticity: A damping mechanism for the transverse head-tail instability

A detailed analytical and numerical study of the suppression of the transverse head-tail instability by modulating the chromaticity over a synchrotron period is presented. We find that a threshold can be developed, and it can be increased to a value larger than the strong head-tail instability threshold. The stability criterion derived agrees very well with the simulations. The underlying physical mechanisms of the damping scheme are rotation of the head-tail phase such that the instability does not occur, and Landau damping due to the incoherent betatron tune spread generated by the varying chromaticity. {copyright} {ital 1997} {ital The American Physical Society

Increase of the transverse strong head-tail stability threshold by an alternating chromaticity

It has been shown that, the transverse head-tail instability can be suppressed by modulating the chromaticity over a synchrotron period. In this work, the authors demonstrate that the threshold of the strong head-tail instability can be significantly increased by the alternating chromaticity (AC). They present results of multi-particle simulation and a new criterion for the SHT instability

About the realization of laser acceleration schemes based on plasmoids in r.f. wells

The laser acceleration of plasmoids is investigated theoretically. Preliminary studies suggest that this configuration, which is based on the forced oscillations of finite pieces of plasma contained in moving or vibrating r.f. wells, has very much simplified plasma physics compared to that of other plasma-based ion acceleration schemes. It is necessary to consider the case when the applied electric field, E, of frequency {omega}, is large, E {le} e/4{pi}{var_epsilon}{sub o}r{lambda}, where r is the Classical electron radius and when the plasma density, n, is high n < 1/r{lambda}{sup 2}. Realization of this proposal requires the development, among other things, of biresonant accelerating systems including oversized single-mode tue-like resonators and the connection of this resonator to a terawatt FELs. If these problems, which will be delineated, are overcome--and progress in optics gives one reason to believe they can be--then gradients of {approximately} 10 GeV/m can be attained. Preliminary design of a linac, based upon this proposal and of a proof-of-principle experiment are presented

CRYSTALLINE BEAMS AT HIGH ENERGIES.

Previously it was shown that by crystallizing each of the two counter-circulating beams, a much larger beam-beam tune shift can be tolerated during the beam-beam collisions; thus a higher luminosity can be reached for colliding beams [1]. On the other hand, crystalline beams can only be formed at energies below the transition energy ({gamma}{sub T}) of the accelerators [2]. In this paper, we investigate the formation of crystals in a high-{gamma}{sub T} lattice that also satisfies the maintenance condition for a crystalline beam [3]

The Longitudinal Stability of Intense Non-Relativistic Particle Bunches in Resistive Structures

The longitudinal stability of intense particle bunches is investigated theoretically in the limit of small wall resistivity compared to total reactance. It is shown that both in the absence of resistivity and to lowest order in the resistance that an intense bunch is stable against longitudinal collective modes. An expression is derived for the lowest order instability rate. Application of these results are made to drivers for heavy ion inertial fusion