Symmetry breaking in crossed magnetic and electric fields

We present the first observations of cylindrical symmetry breaking in highly excited diamagnetic hydrogen with a small crossed electric field, and we give a semiclassical interpretation of this effect. As the small perpendicular electric field is added, the recurrence strengths of closed orbits decrease smoothly to a minimum, and revive again. This phenomenon, caused by interference among the electron waves that return to the nucleus, can be computed from the azimuthal dependence of the classical closed orbits.Comment: 4 page REVTeX file including 5 postscript files (using psfig) Accepted for publication in Physical Review Letters. Difference from earlier preprint: we have discovered the cause of the earlier apparent discrepancy between experiment and theory and now achieve excellent agreemen

Real-world effectiveness of airway clearance techniques in children with cystic fibrosis

Data Availability Statement - The study protocol is published open access. De-identified participant data are hosted in a secure DRE through GOSH DRIVE (www.goshdrive.com). Access to the data, data dictionary and informed consent forms through the DRE is available with permission from the corresponding author.Background Cystic fibrosis (CF) is commonly characterised by thick respiratory mucus. From diagnosis, people with CF are prescribed daily physiotherapy, including airway clearance techniques (ACTs). ACTs consume a large proportion of treatment time, yet the efficacy and effectiveness of ACTs are poorly understood. This study aimed to evaluate associations between the quality and quantity of ACTs and lung function in children and young people with CF. Methods Project Fizzyo, a longitudinal observational cohort study in the UK, used remote monitoring with electronic pressure sensors attached to four different commercial ACT devices to record real-time, breath-by-breath pressure data during usual ACTs undertaken at home over 16 months in 145 children. ACTs were categorised either as conformant or not with current ACT recommendations based on breath pressure and length measurements, or as missed treatments if not recorded. Daily, weekly and monthly associations between ACT category and lung function were investigated using linear mixed effects regression models adjusting for clinical confounders. Results After exclusions, 45 224 ACT treatments (135 individuals) and 21 069 days without treatments (141 individuals) were analysed. The mean±SD age of participants was 10.2±2.9 years. Conformant ACTs (21%) had significantly higher forced expiratory volume in 1 s (FEV1) (mean effect size 0.23 (95% CI 0.19–0.27) FEV1 % pred per treatment) than non-conformant (79%) or missed treatments. There was no benefit from non-conformant or missed treatments and no significant difference in FEV1 between them (mean effect size 0.02 (95% CI −0.01–0.05) FEV1 % pred per treatment). Conclusions ACTs are beneficial when performed as recommended, but most people use techniques that do not improve lung function. Work is needed to monitor and improve ACT quality and to increase the proportion of people doing effective airway clearance at home.UK Research and Innovation MR/T041285/1 Rosetrees Trust M712 Cystic Fibrosis Trust CEA010 Great Ormond Street Hospital for Children Higher Education Funding Council for England KEI2017–01–04 Hospital for Sick Children University College London Partners Awar

Context-dependent nature of destabilizing mutations on the stability of fkbp12

ABSTRACT: The context-dependent nature in which mutations affect protein stability was investigated using the FK506-binding protein, FKBP12. Thirty-four mutations were made at sites throughout the protein, including residues located in the hydrophobic core, the -sheet, and the solvent-exposed face of the R-helix. Urea-induced denaturation experiments were used to measure the change in stability of the mutants relative to that of the wild type (∆∆G U-F ). The results clearly show that the extent of destabilization, or stabilization, is highly context-dependent. Correlations were sought in order to link ∆∆G U-F to various structural parameters. The strongest correlation found was between ∆∆G U-F and N, the number of methyl-(ene) groups within a 6 Å radius of the group(s) deleted. For mutations of buried hydrophobic residues, a correlation coefficient of 0.73 (n ) 16,where n is the number of points) was obtained. This increased to 0.81 (n ) 24) on inclusion of mutations of partially buried hydrophobic residues. These data could be superimposed on data obtained for other proteins for which similarly detailed studies have been performed. Thus, the contribution to stability from hydrophobic side chains, independent of the extent to which a side chain is buried, can be estimated quantitatively using N. This correlation appears to be a general feature of all globular proteins. The effect on stability of mutating polar and charged residues in the R-helix and -sheet was also found to be highly context-dependent. Previous experimental and statistical studies have shown that specific side chains can stabilize the N-caps of R-helices in proteins. Substitutions of Ile56 to Thr and Asp at the N-cap of the R-helix of FKBP12, however, were found to be highly destabilizing. Thus, the intrinsic propensities of an amino acid for a particular element of secondary structure can easily be outweighed by tertiary packing factors. This study highlights the importance of packing density in determining the contribution of a residue to protein stability. This is the most important factor that should be taken into consideration in protein design. To design novel proteins, or rationally alter existing ones, a quantitative understanding of the factors that affect the stability of the native state is required. For proteins without disulfide bonds, noncovalent interactionsssuch as hydrophobic interactions, hydrogen bonds, and electrostatic interactionssdetermine protein stability (1). Protein engineering studies have provided an abundance of information on the relationship between protein structure and stability. Studies on hydrophobic groups (2-13) have shown that the packing of nonpolar groups and burial of hydrophobic surface area are the dominant forces in the stabilization of proteins. Studies on both fully and partially buried hydrophobic residues in barnase, CI2, and staphylococcal nuclease have shown correlations between the change in protein stability upon mutation (∆∆G U-F ) and both the packing density [number of methyl(ene) groups within a certain radius of the nonpolar groups removed

Setting up tunneling conditions by means of Bohmian mechanics

Usually tunneling is established after imposing some matching conditions on the (time-independent) wave function and its first derivative at the boundaries of a barrier. Here an alternative scheme is proposed to determine tunneling and estimate transmission probabilities in time-dependent problems, which takes advantage of the trajectory picture provided by Bohmian mechanics. From this theory a general functional expression for the transmission probability in terms of the system initial state can be reached. This expression is used here to analyze tunneling properties and estimate transmissions in the case of initial Gaussian wave packets colliding with ramp-like barriers.Comment: 18 pages, 4 figure

Power Laws, Precursors and Predictability During Failure

We investigate the dynamics of a modified Burridge-Knopoff model by introducing a dissipative term to mimic the bursts of acoustic emission (AE) from rock samples. The model explains many features of the statistics of AE signals observed in experiments such as the crossover in the exponent value from relatively small amplitude AE signals to larger regime, and their dependence on the pulling speed. Significantly, we find that the cumulative energy dissipated identified with acoustic emission can be used to predict a major slip event. We also find a data collapse of the acoustic activity for several major slip events describable by a universal stretched exponential with corrections in terms of time-to-failure.Comment: 7 pages, 6 figures, Final version with minor change