A comprehensive comparison of methods for clearing effects on reflected airblast impulse

Having calculated the free-field pressure history at the location of a building, an engineer engaged in design or assessment of that building must then calculate the loads on the various surfaces of the structure. Numerous engineering methods have been developed that provide approximate (and generally conservative) approaches towards the calculation of these loads. Of greatest importance is the load on the front face (i.e., the building surface directly facing the explosion source). Depending on the size of the building and the blast load duration, clearing effects due to the building’s boundaries may reduce the reflected impulse on the front face from the fully reflected value predicted by standard blast models. Unfortunately, there are many methods available in the literature for evaluating clearing effects, each using somewhat similar, yet distinctly different, equations. One approach given in UFC 3-340-02 (and reproduced in UFC 3-340-01) has gained widespread acceptance; another is presented in a set of guidelines published by ASCE and used for industrial applications; and lastly, a formerly classified study dating back to 1955 which, although declassified in 1998, seems to have escaped the notice of the blast community. The focus of the present paper is to evaluate all three of these methods empirically, by comparing their results against a series of blast tests with varying charge weights and scaled reflecting building dimensions. A comparative evaluation is then made of the strengths and weaknesses of each approach, with recommendations for future use by researchers and blast engineers

Rapid faecal transmission and invasive amoebiasis in Durban

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Inflationary potentials in DBI models

We study DBI inflation based upon a general model characterized by a power-law flow parameter $\epsilon(\phi)\propto\phi^{\alpha}$ and speed of sound $c_s(\phi)\propto\phi^{\beta}$, where $\alpha$ and $\beta$ are constants. We show that in the slow-roll limit this general model gives rise to distinct inflationary classes according to the relation between $\alpha$ and $\beta$ and to the time evolution of the inflaton field, each one corresponding to a specific potential; in particular, we find that the well-known canonical polynomial (large- and small-field), hybrid and exponential potentials also arise in this non-canonical model. We find that these non-canonical classes have the same physical features as their canonical analogs, except for the fact that the inflaton field evolves with varying speed of sound; also, we show that a broad class of canonical and D-brane inflation models are particular cases of this general non-canonical model. Next, we compare the predictions of large-field polynomial models with the current observational data, showing that models with low speed of sound have red-tilted scalar spectrum with low tensor-to-scalar ratio, in good agreement with the observed values. These models also show a correlation between large non-gaussianity with low tensor amplitudes, which is a distinct signature of DBI inflation with large-field polynomial potentials.Comment: Minor changes, reference added. Version submitted to JCA

Measurement of the 40Ca(3He,t)40Sc reaction

Levels in [Formula Presented] below 2.5 MeV excitation energy have been populated in a high-resolution study of the [Formula Presented] reaction. Three new states have been observed at energies [Formula Presented] 1871, and 1925 keV. Correspondence of the observed [Formula Presented] levels with known [Formula Presented] states in [Formula Presented] and [Formula Presented] are based on predictions provided by the isobaric multiplet mass equation. Our results confirm recently estimated stellar reaction rates for proton capture on [Formula Presented]

Investigation of the23Na(p, γ)24Mg and 23Na(p, α)20Ne reactions via (3He,d) spectroscopy

States near the 23Na+p threshold in 24Mg were investigated using the 23Na(3He,d)24Mg reaction over the angular range of 5° ≤ θlab ≤ 35° at E(3He)=20 MeV. Spectroscopic factors were extracted for states corresponding to resonances in the 23Na(p, γ) 24Mg and 23Na(p, α)20Ne reactions. We find that one state, corresponding to a previously unobserved resonance at Ec.m.= 138 keV, may make a significant contribution to the rates of both reactions at low temperatures. Another state, corresponding to a possible resonance at Ec.m.=37 keV may make a small contribution to the 23Na(p, α)20Ne reaction. New rates for the 23Na(p, γ)24Mg and 23Na(p, α) 20Ne reactions are presented and the astrophysical implications are discussed

Investigation of the 22Ne(p,y)23Na reaction via a (3He,d) spectroscopy

States near the [Formula Presented] threshold in [Formula Presented] were investigated using the [Formula Presented] reaction over the angular range of [Formula Presented] at [Formula Presented] Spectroscopic factors were extracted for states corresponding to resonances in the [Formula Presented] reaction. Two previously suggested resonances at [Formula Presented] and 100 keV were not observed at any angle. A new rate for the [Formula Presented] reaction has been calculated and its implications are discussed

Reciprocal effects of silicon supply and endophytes on silicon accumulation and Epichloë colonization in grasses

Cool season grasses associate asymptomatically with foliar Epichloë endophytic fungi in a symbiosis where Epichloë spp. protects the plant from a number of biotic and abiotic stresses. Furthermore, many grass species can accumulate large quantities of silicon (Si), which also alleviates a similar range of stresses. While Epichloë endophytes may improve uptake of minerals and nutrients, their impact on Si is largely unknown. Likewise, the effect of Si availability on Epichloë colonization remains untested. To assess the bidirectional relationship, we grew tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) hydroponically with or without Si. Grasses were associated with five different Epichloë endophyte strains [tall fescue: AR584 or wild type (WT); perennial ryegrass: AR37, AR1, or WT] or as Epichloë-free controls. Reciprocally beneficial effects were observed for tall fescue associations. Specifically, Epichloë presence increased Si concentration in the foliage of tall fescue by at least 31%, regardless of endophyte strain. In perennial ryegrass, an increase in foliar Si was observed only for plants associated with the AR37. Epichloë promotion of Si was (i) independent of responses in plant growth, and (ii) positively correlated with endophyte colonization, which lends support to an endophyte effect independent of their impacts on root growth. Moreover, Epichloë colonization in tall fescue increased by more than 60% in the presence of silicon; however, this was not observed in perennial ryegrass. The reciprocal benefits of Epichloë-endophytes and foliar Si accumulation reported here, especially for tall fescue, might further increase grass tolerance to stress

14N(3He,d)15O as a probe of direct capture in the 14N(p,γ)15O reaction

Spectroscopic factors and asymptotic normalization coefficients (ANCs) have been determined for bound states in 15O using the 14N(3He,d)15O reaction. These results are used to calculate the astrophysical S factor for direct capture in the 14N(p, γ)13O reaction. We also discuss how uncertainties in optical-model parameters influence both the spectroscopic factors and the ANCs, and the effect that this has on the predicted direct-capture reaction rate

Mycorrhizal fungi compromise production of endophytic alkaloids, increasing plant susceptibility to an aphid herbivore

1. Symbiosis plays a critical role in plant biology. Temperate grasses often associate with several symbiotic fungi simultaneously, including Epichloë endophytes and arbuscular mycorrhizal (AM) fungi, in shoots and roots, respectively. These symbionts often modulate plant–herbivore interactions by influencing nutritional traits (i.e. AM fungi-mediated nutrient uptake) and/or the secondary chemistry (i.e. endophytic alkaloids) of their host plant. Moreover, such grasses also accumulate large amounts of silicon (Si) from the soil, which can be deposited in tissues to act as a physical anti-herbivore defence. 2. Recent evidence suggests that both endophytes and AM fungi independently facilitate Si uptake. However, the consequences of their interactions with piercing-sucking insects (i.e. aphids), or whether Si supply, endophytes, and AM fungi interact in this regard, are currently unknown. While Si deposition may be less effective against aphids than other herbivores (i.e. chewing caterpillars), Si supply can also alter plant secondary metabolite defences, which could affect sucking insects. 3. In a factorial greenhouse experiment, we evaluated whether these components, acting alone or in combination, altered (1) foliar primary chemistry, (2) Si and symbiont-chemical (endophytic alkaloids) defences, as well as (3) performance of the bird cherry-oat aphid (Rhopalosiphum padi) feeding on tall fescue (Festuca arundinacea). 4. Endophytes decreased all aphid performance parameters, including population growth and reproduction by 40%, but their impact was reversed by the presence of AM fungi, leading to a 52% increase in aphid performance compared with plants solely hosting endophytes. This improvement in performance was associated with reduced loline alkaloid levels and higher shoot nitrogen in AM-endophytic plants. Endophytes and AM fungi exhibited antagonism, with endophytes reducing AM colonization by 34% and AM presence decreasing endophyte loline alkaloids by 44%. While both fungi jointly increased Si accumulation by 39% under Si-supplied conditions, Si had no noticeable effects on aphids. Moreover, although Si supply had no identifiable effects on AM colonization, it reduced endophyte peramine alkaloids by 24%. 5. Synthesis. Our findings indicate that symbiotic fungal partnerships and silicon provision may benefit plants but could weaken anti-herbivore defences when combined. Revealing the complex interactions among diverse fungal symbionts and showcasing their effects on different anti-herbivore defences (chemical and physical) and herbivore performance for the first time