4,092 research outputs found
Axion-like-particle decay in strong electromagnetic backgrounds
The decay of a massive pseudoscalar, scalar and U(1) boson into an
electron-positron pair in the presence of strong electromagnetic backgrounds is
calculated. Of particular interest is the constant-crossed-field limit,
relevant for experiments that aim to measure high-energy axion-like-particle
conversion into electron-positron pairs in a magnetic field. The total
probability depends on the quantum nonlinearity parameter - a product of field
and lightfront momentum invariants. Depending on the seed particle mass,
different decay regimes are identified. In the below-threshold case, we find
the probability depends on a non-perturbative tunnelling exponent depending on
the quantum parameter and the particle mass. In the above-threshold case, we
find that when the quantum parameter is varied linearly, the probability
oscillates nonlinearly around the spontaneous decay probability. A strong-field
limit is identified in which the threshold is found to disappear. In modelling
the fall-off of a quasi-constant-crossed magnetic field, we calculate
probabilities beyond the constant limit and investigate when the decay
probability can be regarded as locally constant.Comment: 22 pages, 7 figure
Temperature-dependent rate coefficients for the reactions of the hydroxyl radical with the atmospheric biogenics isoprene, alpha-pinene and delta-3-carene
Pulsed laser methods for OH generation and detection were used to study atmospheric degradation reactions for three important biogenic gases: OHCisoprene (Reaction R1), OH+α-pinene (Reaction R2) and OH+Î- 3-carene (Reaction R3). Gas-phase rate coefficients were characterized by non-Arrhenius kinetics for all three reactions. For (R1), k1 (241-356 K)= (1:93±0:08)Ă 10-11 exp{(466±12)/T} cm3 molecule-1 s-1 was determined, with a room temperature value of k1 (297 K)= (9:3± 0:4)Ă10-11 cm3 molecule-1 s-1, independent of bath-gas pressure (5-200 Torr) and composition (MDN2 or air). Accuracy and precision were enhanced by online optical monitoring of isoprene, with absolute concentrations obtained via an absorption cross section, αisoprene = (1:28±0:06)Ă 10-17 cm2 molecule-1 at λ = 184:95 nm, determined in this work. These results indicate that significant discrepancies between previous absolute and relative-rate determinations of k1 result in part from Ï values used to derive the isoprene concentration in high-precision absolute determinations. Similar methods were used to determine rate coefficients (in 10-11 cm3 molecule-1 s-1/ for (R2)-(R3): k2 (238-357 K)= (1:83±0:04) Ăexp{(330±6)/T } and k3 (235-357 K)= (2:48±0:14) Ăexp{(357±17)/T }. This is the first temperature-dependent dataset for (R3) and enables the calculation of reliable atmospheric lifetimes with respect to OH removal for e.g. boreal forest springtime conditions. Room temperature values of k2 (296 K)= (5:4±0:2) Ă10-11 cm3 molecule-1 s-1 and k3 (297 K)= (8:1±0:3)Ă10-11 cm3 molecule-1 s-1 were independent of bathgas pressure (7-200 Torr, N2 or air) and in good agreement with previously reported values. In the course of this work, 184.95 nm absorption cross sections were determined: Ï = (1:54±0:08) Ă10-17 cm2 molecule-1 for α-pinene and (2:40±0:12)Ă10-17 cm2 molecule-1 for 1-3-carene
The impact of broadband in schools
The report reviews evidence for the impact of broadband in English schools, exploring; Variations in provision in level of broadband connectivity; Links between the level of broadband activity and nationally accessible performance data; Aspects of broadband connectivity and the school environment that contribute to better outcomes for pupils and teachers; Academic and motivational benefits associated with educational uses of this technology
Hydrochlorination of ruthenaphosphaalkenyls: unexpectedly facile access to alkylchlorohydrophosphane complexes
The novel ruthenaphosphaalkenyls [Ru{PâC(H)SiMe2R}Cl- (CO)(PPh3)2] (R = p-C6H4CF3, nBu) have been prepared for the first time, and studied alongside precedent analogues (R = Me, Ph, p-tol) for their reactions with HCl. In contrast to chemistry defined for the tert-butyl congener [Ru{PâC(H)tBu}Cl(CO)(PPh3)2], which initially adds a single equivalent of HCl across the RuâP linkage, all five silyl derivatives undergo spontaneous addition of a second equivalent to afford [Ru{η1-PHClâCH2SiMe2R}Cl(CO)(PPh3)2], extremely rare examples of coordinated âPHXRâ type ligands. Where R = SiMe3, a distorted octahedral geometry with a conformationally restricted âPHXRâ ligand is observed crystallographically; this structure is appreciably retained in solution, as determined from multinuclear NMR spectroscopic features, which include a Karplus-like PPh3âRuâPâH spinâspin coupling dependence. Computational data suggest a silyl-induced increase in negative charge density at the phosphaalkenic carbon, rather than an intrinsic thermodynamic driver, as the likely origin of the disparate reactivity
Surface temperature measurements using a thin film thermal array
A thin film device was designed and fabricated to measure surface temperatures. An array of eight integrated thermal sensors are mounted on a 0.002 inch (0.05 mm) Kapton film and multiplexed to obtain an area thermal measurement. The device was tested on a flat plate airfoil and demonstrated a temperature variation of 0.55 C maximum and 0.05 C minimum compared to embedded thermocouples. Future improvements are also discussed
The Impacts of Wrist Wrap Type and Sex on Bench Press Muscular Strength and Power
While wrist wraps have become increasingly prevalent in both competitive and recreational demographics, their posited ability to augment bench press performance by enhanced wrist stability still remains unclear. PURPOSE: To determine the effect of varying wrap styles on bench-specific muscular strength and associated power, as well as quantitative and subjective differences between sexes. METHODS: Eighteen resistance trained males and females (9M/9F; 24±4y; 176±33cm; 80±15kg) visited the laboratory on three separate occasions in randomized, crossover, and counterbalanced design to sport either a flexible wrist wrap (FW), stiff wrap (SW), or a no wrap control (NW) condition. All participants underwent a bench press one-repetition maximum (1RM) test and linear position transducer-derived peak power and velocity assessments. Furthermore, subjective stability (SS) and discomfort (SD) were determined promptly following 1RM attempts. Bench press performance and sex-collapsed subjective variables were analyzed using a two-way (condition x sex) mixed model ANOVA with repeated measures and a nonparametric Friedmanâs ANOVA, respectively. Both analyses were performed at a p\u3c.05 significance level. RESULTS: Analyses failed to detect any main condition or interaction effects for bench press 1RM, however, a statistically significant main sex effect was observed (p\u3c.001; ηp2=.597) favoring males relative to females (p\u3c.001; 114±22kg vs 68±16kg). Both peak power and velocity failed to reveal any significant main condition or sex effects, nor any interactions. Nonparametric assessments further revealed significant wrist wrap condition effects for both SS (p\u3c.001; Kendallâs W=.628) and SD (p\u3c.001; Kendallâs W=.935), whereby NW was statistically more comfortable (p\u3c.001) than either wrap condition, without any difference between DW and SW (p\u3e.05). CONCLUSION: Although wrist wraps did not significantly alter bench press-specific strength and power, participants nonetheless perceived wrist wraps as subjectively more stable irrespective of increased discomfort.
ACKNOWLEDGEMENTS: The authors of this abstract would like to thank Peter Spence and SBD Apparel for generously donating the wrist wraps utilized in the present investigation
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