Interim Report on Fatigue Characteristics of a Typical Metal Wing

Constant amplitude fatigue tests of seventy-two P-51D "Mustang" wings are reported. The tests were performed by a vibrational loading system and by an hydraulic loading device for conditions with and without varying amounts of pre-load. The results indicate that: (a) the frequency of occurrence of fatigue at any one location is related to the range of the loads applied, (b) the rate of propagation of visible cracks is more or less constant for a large portion of the life of the specimen, (c) the fatigue strength of the structure is similar to that of notched material having a theoretical stress concentration factor of more than 3.0, (d) the frequency distribution of fatigue life is approximately logarithmic normal, (e) the relative increase in fatigue life for a given pre-load depends on the maximum load of the loading cycle only, while the optimum pre-load value is approximately 85 percent of the ultimate failing load, and (f) that normal design procedure will not permit the determination of local stress levels with sufficient accuracy to determine the fatigue strength of an element of a redundant structure

NAP1 Modulates Binding of Linker Histone H1 to Chromatin and Induces an Extended Chromatin Fiber Conformation

NAP1 (nucleosome assembly protein 1) is a histone chaperone that has been described to bind predominantly to the histone H2A·H2B dimer in the cell during shuttling of histones into the nucleus, nucleosome assembly/remodeling, and transcription. Here it was examined how NAP1 interacts with chromatin fibers isolated from HeLa cells. NAP1 induced a reversible change toward an extended fiber conformation as demonstrated by sedimentation velocity ultracentrifugation experiments. This transition was due to the removal of the linker histone H1. The H2A·H2B dimer remained stably bound to the native fiber fragments and to fibers devoid of linker histone H1. This was in contrast to mononucleosome substrates, which displayed a NAP1-induced removal of a single H2A·H2B dimer from the core particle. The effect of NAP1 on the chromatin fiber structure was examined by scanning/atomic force microscopy. A quantitative image analysis of ∼36,000 nucleosomes revealed an increase of the average internucleosomal distance from 22.3 ± 0.4 to 27.6 ± 0.6 nm, whereas the overall fiber structure was preserved. This change reflects the disintegration of the chromatosome due to binding of H1 to NAP1 as chromatin fibers stripped from H1 showed an average nucleosome distance of 27.4 ± 0.8 nm. The findings suggest a possible role of NAP1 in chromatin remodeling processes involved in transcription and replication by modulating the local linker histone content

Impacts of free tropospheric turbulence parametrisation on a sheared tropical cyclone

The turbulent transport of momentum, heat, and moisture can impact tropical cyclone intensity. However, representing subgrid-scale turbulence accurately in numerical weather prediction models is challenging due to a lack of observational data. To address this issue, a case study of Hurricane Maria was conducted to analyse the influence of different free tropospheric turbulence parametrisations on sheared tropical cyclones. The study used the current Met Office Unified Model (MetUM) parametrisation, as well as a parametrisation scheme with significantly reduced free tropospheric mixing length. Convection-permitting ensemble simulations were performed for both mixing schemes at two initialisation times (four 18-member ensembles in total), revealing an improvement in the intensity forecasts of Hurricane Maria when the mixing length was decreased in the free troposphere. By implementing this change, the less diffuse simulations presented a drier mid-level. The resolved downward transport of drier air from the mid-levels into the inflow layer (so-called “downdraft ventilation”) was thus more effective in reducing the storm's intensity. In contrast to earlier studies, where decreasing the diffusivity in the boundary layer intensified the storm, we show that decreasing the free tropospheric diffusivity can weaken the storm by enhancing shear-related weakening processes. While this study was performed using the MetUM, the findings highlight the general importance of considering turbulence parametrisation, and show that changes in diffusivity can have different impacts on storm intensity depending on the environment and where the changes are applied

Synthesis and analysis of the anticancer activity of platinum(ii) complexes incorporating dipyridoquinoxaline variants

Eight platinum(ii) complexes with anticancer potential have been synthesised and characterised. These complexes are of the type [Pt(I)(A)], where I is either dipyrido[3,2-f:2′,3′-h]quinoxaline (dpq) or 2,3-dimethyl-dpq (23Medpq) and A is one of the R,R or S,S isomers of either 1,2-diaminocyclohexane (SS-dach or RR-dach) or 1,2-diaminocyclopentane (SS-dacp or RR-dacp). The CT-DNA binding of these complexes and a series of other complexes were assessed using fluorescent intercalator displacement assays, resulting in unexpected trends in DNA binding affinity. The cytotoxicity of the eight synthesised compounds was determined in the L1210 cell line; the most cytotoxic of these were [Pt(dpq)(SS-dach)]Cl and [Pt(dpq)(RR-dach)]Cl, with IC values of 0.19 and 0.80 μM, respectively. The X-ray crystal structure of the complex [Pt(dpq)(SS-dach)](ClO)·1.75HO is also reported. This journal i

Self-assembly of an imidazolate-bridged FeIII/CuII heterometallic cage

A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [CuFeL](ClO)χ solvent (HL = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl} amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy

Ensemble prediction for nowcasting with a convection-permitting model - II: forecast error statistics

A 24-member ensemble of 1-h high-resolution forecasts over the Southern United Kingdom is used to study short-range forecast error statistics. The initial conditions are found from perturbations from an ensemble transform Kalman filter. Forecasts from this system are assumed to lie within the bounds of forecast error of an operational forecast system. Although noisy, this system is capable of producing physically reasonable statistics which are analysed and compared to statistics implied from a variational assimilation system. The variances for temperature errors for instance show structures that reflect convective activity. Some variables, notably potential temperature and specific humidity perturbations, have autocorrelation functions that deviate from 3-D isotropy at the convective-scale (horizontal scales less than 10 km). Other variables, notably the velocity potential for horizontal divergence perturbations, maintain 3-D isotropy at all scales. Geostrophic and hydrostatic balances are studied by examining correlations between terms in the divergence and vertical momentum equations respectively. Both balances are found to decay as the horizontal scale decreases. It is estimated that geostrophic balance becomes less important at scales smaller than 75 km, and hydrostatic balance becomes less important at scales smaller than 35 km, although more work is required to validate these findings. The implications of these results for high-resolution data assimilation are discussed

Heteroatom substitution effects in spin crossover dinuclear complexes

We probe the effect of heteroatom substitution on the spin crossover (SCO) properties of dinuclear materials of the type [Fe2(NCX)4(R-trz)5]·S (X = S, Se; S = solvent; R-trz = (E)-N-(furan-2-ylmethylene)- 4H-1,2,4-triazol-4-amine (furtrz); (E)-N-(thiophen-2-ylmethylene)-4H-1,2,4-triazole-4-amine (thtrz)). For the furtrz family ([Fe2(NCX)4(furtrz)5]·furtrz·MeOH; X = S (furtrz-S) and X = Se (furtrz-Se)) gradual and incomplete one-step SCO transitions are observed (furtrz-S (T1/2 = 172 K) and furtrz-Se (T1/2 = 205 K)) and a structural evolution from [HS-HS] to [HS-LS] per dinuclear species. Contrasting this, within the thtrz family ([Fe2(NCX)4(thtrz)5]·4MeOH; X = S (thtrz-S) and X = Se (thtrz-Se)) more varied SCO transitions are observed, with thtrz-S being SCO-inactive (high spin) and thtrz-Se showing a rare complete two-step SCO transition (T1/2(1,2) = 170, 200 K) in which the FeII sites transition from [HS-HS] to [HS-LS] to [LS-LS] per dinuclear unit with no long range ordering of spin-states at the intermediate plateau. Detailed structure- function analyses have been conducted within this growing dinuclear family to rationalise these diverse spin-switching properties

Treating sample covariances for use in strongly coupled atmosphere-ocean data assimilation

Strongly coupled data assimilation requires cross-domain forecast error covariances; information from ensembles can be used, but limited sampling means that ensemble derived error covariances are routinely rank deficient and/or ill-conditioned and marred by noise. Thus they require modification before they can be incorporated into a standard assimilation framework. Here, we compare methods for improving the rank and conditioning of multivariate sample error covariance matrices for coupled atmosphere-ocean data assimilation. The first method, reconditioning, alters the matrix eigenvalues directly; this preserves the correlation structures but does not remove sampling noise. We show it is better to recondition the correlation matrix rather than the covariance matrix as this prevents small but dynamically important modes from being lost. The second method, model state-space localisation via the Schur product, effectively removes sample noise but can dampen small cross-correlation signals. A combination that exploits the merits of each is found to offer an effective alternative

A low-order model investigation of the analysis of gravity waves in the ensemble Kalman filter.

The behavior of the ensemble Kalman filter (EnKF) is examined in the context of a model that exhibits a nonlinear chaotic (slow) vortical mode coupled to a linear (fast) gravity wave of a given amplitude and frequency. It is shown that accurate recovery of both modes is enhanced when covariances between fast and slow normal-mode variables (which reflect the slaving relations inherent in balanced dynamics) are modeled correctly. More ensemble members are needed to recover the fast, linear gravity wave than the slow, vortical motion. Although the EnKF tends to diverge in the analysis of the gravity wave, the filter divergence is stable and does not lead to a great loss of accuracy. Consequently, provided the ensemble is large enough and observations are made that reflect both time scales, the EnKF is able to recover both time scales more accurately than optimal interpolation (OI), which uses a static error covariance matrix. For OI it is also found to be problematic to observe the state at a frequency that is a subharmonic of the gravity wave frequency, a problem that is in part overcome by the EnKF.However, error in themodeled gravity wave parameters can be detrimental to the performance of the EnKF and remove its implied advantages, suggesting that a modified algorithm or a method for accounting for model error is needed