Transferability of decompression wave speed measured by a small-diameter shock tube to full size pipelines and implications for determining required fracture propagation resistance

The control of propagating ductile (or tearing) fracture is a fundamental requirement in the fracture control design of pipelines. The Battelle two-curve method developed in the early 1970s still forms the basis of the analytical framework used throughout the industry. GASDECOM is typically used for calculating decompression speed, and idealizes the decompression process as isentropic and one-dimensional, taking no account of frictional effects. While this approximation appears not to have been a major issue for large-diameter pipes and for moderate pressures (up to 12 MPa), there have been several recent full-scale burst tests at higher pressures and smaller diameters for which the measured decompression velocity has deviated progressively from the predicted values, in general towards lower velocities. The present research was focused on determining whether pipe diameter was a major factor that could limit the applicability of frictionless models such as GASDECOM. Since potential diameter effects are primarily related to wall friction, which in turn is related to the ratio of surface roughness-to-diameter, an experimental approach was developed based on keeping the diameter constant, at a sufficiently small value to allow for an economical experimental arrangement, and varying the internal roughness. A series of tests covering a range of nominal initial pressures from 10 to 21 MPa, and involving a very lean gas and three progressively richer compositions, were conducted using two specialized high-pressure shock tubes (42 m long, I.D. = 38.1 mm). The first is honed to an extremely smooth surface finish, in order to minimize frictional effects and better simulate the behaviour of larger-diameter pipelines, while the second has a higher internal surface roughness. The results show that decompression wave speeds in the rough tube are consistently slower than those in the smooth tube under the same conditions of mixture composition and initial pressure &; temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation indicates that the primary reason for the slower decompression wave speed in the rough tube is the higher spatial gradient of pressure pertaining to the decompression wave dynamics, particularly at lower pressure ratios and higher gas velocities. The magnitude of the effect of the slower decompression speed on arrest toughness was then evaluated by a comparison involving several hypothetical pipeline designs, and was found to be potentially significant for pipe sizes DN 450 and smaller.     

Gut feelings about recovery after stroke: the organization and reorganization of human swallowing motor cortex

Swallowing problems can affect as many as one in three patients in the period immediately after a stroke. In some cases this can lead to serious morbidity, in particular malnutrition and pulmonary aspiration. Despite this, swallowing usually recovers completely in the vast majority of patients within weeks. This impressive propensity for recovery is likely to relate to how the area of the motor cortex concerned with swallowing is organized and then reorganized after cerebral injury. Recent studies have indicated that swallowing has a bilateral but asymmetric inter-hemisphere representation within motor and premotor cortex. Damage to the hemisphere that has the greater swallowing output appears to predispose that individual to swallowing problems. However, because there is additional substrate for swallowing in the undamaged hemisphere, the capacity for compensatory reorganization in the contralateral motor cortex might be increased, leading to a greater likelihood of recovery. Swallowing might be an excellent system for studying cortical plasticity, and might prove useful in the development of new therapies aimed at accelerating reorganization in the undamaged hemisphere after unilateral cerebral injury.     

Whole body metabolic responses to brain trauma in the rat

Hotien prefecture, Xinjiang Province, China, in the Taklamakan Desert, is an area of severe iodine deficiency. Because usual methods of iodine supplementation failed here, we began supplementation in 1992 with potassium iodate, which was added to irrigation water (Lancet 1994; 334:107-110). We report 4 y experience with this method in 3 townships that contained a total treated population of 37,000. Potassium iodate was dripped into irrigation water (to a concentration 10-80 microg/l) during a 2- to 4-wk period. During the 3 y that followed, no further supplementation was made, and iodine concentrations increased several fold in crops and plants, sheep and chicken thyroid glands, and meat and in urine of children 2-6 y of age and of women who were of childbearing age. Infant mortality decreased 50%, and sheep production increased 43%. Iodine repletion of soil through irrigation water is an effective and cost-efficient way of providing iodine in appropriate situations.     

Efficacy of zeta-cypermethrin as pour-on or spray formulations for the control of buffalo fly (Haematobia irritans exigua) in cattle

OBJECTIVE: To determine the efficacy of zeta-cypermethrin in controlling buffalo fly (Haematobia irritans exigua). DESIGN: Five field trials in northern and central Queensland. PROCEDURE: Zeta-cypermethrin pour-on at 2.5 mg/kg, spray at 62.5 ppm, deltamethrin pour-on and pour-on vehicle were applied to groups of 20 cattle. Buffalo fly counts were conducted three times before treatment and 3, 7, 14, 21, 28 and 35 days after treatment. RESULTS: In central Queensland where synthetic pyrethroid resistance in buffalo fly populations was rare, 2.5 mg/kg of zeta-cypermethrin pour-on gave good control of buffalo fly for 4 weeks and was better than a deltamethrin product. A zeta-cypermethrin spray used at 62.5 ppm gave 14 days control. In far-north Queensland where resistance to synthetic pyrethroids and heavy rain was common, the maximum period of efficacy of zeta-cypermethrin pour-on was reduced to 2 weeks. CONCLUSION: In areas where there is low resistance to synthetic pyrethroids among buffalo flies, zeta-cypermethrin pour-on can be expected to give good control for 4 weeks.     

Propriospinal myoclonus: evidence for spinal "pattern" generators in humans

The clinical and electrophysiological characteristics of eight patients with propriospinal myoclonus are described. Myoclonus developed within days or weeks of cervical trauma in half the patients. Seven cases had axial flexion jerks, and one axial extension jerks. Myoclonic EMG activity consisted of repetitive bursts with a frequency of 1-7 Hz. The jerks in three of the cases were comprised of alternating and rhythmic bursts of EMG activity in rectus abdominis and the paraspinal muscles. From these new observations, it is proposed that cervical trauma can lead to the partial release of a spinal pattern generator. The latter is capable of recruiting muscles through long propriospinal pathways into complex rhythmic activity.     

Scattering of TE-polarized EM wave by discontinuity in groundeddielectric layer

The two-dimensional problem of EM wave interaction with a dielectric discontinuity in an infinite grounded dielectric layer is studied. An electric field integral equation (EFIE) for TE illumination has been derived based on the Green's function for the electric field produced by induced polarization currents in the discontinuity region. Impressed electric fields consist of either plane waves incident from space above the dielectric layer or surface waves supported by that layer. Method of Moments (MoM) numerical solutions for the induced electric field in the discontinuity region are implemented. The amplitudes of surface waves excited by excess discontinuity-region polarization currents are calculated, as well as the pattern of the scattered field and the associated scattering width. It is observed that the excitation of a surface-wave mode reduces the back scattered radiation for TE-polarized plane wave incidence. The accuracy of the theory is verified by comparison of numerical results with those of existing studies     

Clinical and angiographic predictors of stroke and death from carotid endarterectomy: systematic review

OBJECTIVE: To identify risk factors for operative stroke and death from carotid endarterectomy. DESIGN: Systematic review of all studies published since 1980 which related risk of stroke and death to various preoperative clinical and angiographic characteristics, including unpublished data on 1729 patients from the European carotid surgery trial. MAIN OUTCOME MEASURE: Operative risk of stroke and death. RESULTS: Thirty six published studies fulfilled our criteria. The effect of 14 potential risk factors was examined. The odds of stroke and death were decreased in patients with ocular ischaemia alone (amaurosis fugax or retinal artery occlusion) compared with those with cerebral transient ischaemic attack or stroke (seven studies; odds ratio 0.49; 95% confidence interval 0.37 to 0.66; P < 0.00001). The odds were increased in women (seven studies; 1.44; 1.14 to 1.83; P < 0.005), subjects aged > or = 75 years (10 studies: 1.36; 1.09 to 1.71; P < 0.01), and with systolic blood pressure > 180 mm Hg (four studies; 1.82; 1.37 to 2.41; P < 0.0001), peripheral vascular disease (one study; 2.19; 1.40 to 3.60; P < 0.0005), occlusion of the contralateral internal carotid artery (14 studies; 1.91; 1.35 to 2.69; P < 0.0001), stenosis of the ipsilateral internal carotid siphon (five studies; 1.56; 1.03 to 2.36; P = 0.02), and stenosis of the ipsilateral external carotid artery (one study; 1.61; 1.05 to 2.47; P = 0.03). Operative risk was not significantly related to presentation with cerebral transient ischaemic attack versus stroke, diabetes, angina, recent myocardial infarction, current cigarette smoking, or plaque surface irregularity at angiography. Multiple regression analysis of data from the European carotid surgery trial identified cerebral versus ocular events at presentation, female sex, systolic hypertension, and peripheral vascular disease as independent risk factors. CONCLUSIONS: The risk of stroke and death from carotid endarterectomy is related to several clinical and angiographic characteristics. These observations may help clinicians to estimate operative risks for individual patients and will also facilitate more meaningful comparison of the operative risks of different surgeons or at different institutions by allowing some adjustment for differences in case mix.     

Self-structuring antennas

This paper introduces a new class of antennas, called self-structuring antennas (SSAs). An SSA has the ability to alter its electrical shape in response to changes in its environment. This property makes an SSA suitable for use in a number of traditionally difficult antenna situations. The basic principles of the SSA are introduced, and a number of potential applications are highlighted. Details of a simple prototype antenna are provided. Computer tools capable of analyzing the SSA are described, and results of both numerical and experimental investigations of the SSA are presented     

Arsenic retention and release in ombrotrophic peatlands

Organic matter can play an important role in the mobility and fate of As in the environment, but there is a lack of data on As biogeochemistry in ombrotrophic peatlands. The aim of this study was to investigate As retention and release in atmospherically contaminated ombrotrophic peat soils in the Peak District National Park (UK). Solid phase As concentrations in the peat soils exceed 25 mg kg^− 1. Solid phase As and Fe concentrations are closely correlated at sites where the peat is subjected to drying and oxic conditions. In a wetter zone of the bog, solid phase As and Fe distributions are decoupled, suggesting that As retention in these systems is not solely controlled by the presence of Fe oxides. Comparison of solid phase As and Pb distributions reveals that As has been subjected to post-depositional mobility in areas of water table fluctuation. Conversely, at permanently waterlogged locations As is immobile. Detailed stream water sampling reveals that As is released from the organic-rich uplands soils into the fluvial system. Dissolved As concentrations are highly variable, with values ranging from 0.20 to 7.28 μg l^− 1. Stream water As concentrations are elevated during late summer stormflow periods when there has been re-wetting of the peat after significant water table draw-down. Dissolved As is strongly correlated to dissolved organic carbon under stormflow and baseflow. The results of this study suggest that organic matter plays an important role in As dynamics in ombrotrophic peatlands, but further work is needed to identify the exact As binding and release mechanisms. Drying and re-wetting of ombrotrophic peat soils and associated changes in redox status has the potential to lead to increased As mobility. Further work is needed to provide information on how predicted climate change will influence As cycling at sites containing a legacy of atmospheric contamination.     

Live analysis of free centrosomes in normal and aphidicolin-treated Drosophila embryos

In a number of embryonic systems, centrosomes that have lost their association with the nuclear envelope and spindle maintain their ability to duplicate and induce astral microtubules. To identify additional activities of free centrosomes, we monitored astral microtubule dynamics by injecting living syncytial Drosophila embryos with fluorescently labeled tubulin. Our recordings follow multiple rounds of free centrosome duplication and separation during the cortical division. The rate and distance of free sister centrosome separation corresponds well with the initial phase of associated centrosome separation. However, the later phase of separation observed for centrosomes associated with a spindle (anaphase B) does not occur. Free centrosome separation regularly occurs on a plane parallel to the plasma membrane. While previous work demonstrated that centrosomes influence cytoskeletal dynamics, this observation suggests that the cortical cytoskeleton regulates the orientation of centrosome separation. Although free centrosomes do not form spindles, they display relatively normal cell cycle-dependent modulations of their astral microtubules. In addition, free centrosome duplication, separation, and modulation of microtubule dynamics often occur in synchrony with neighboring associated centrosomes. These observations suggest that free centrosomes respond normally to local nuclear division signals. Disruption of the cortical nuclear divisions with aphidicolin supports this conclusion; large numbers of abnormal nuclei recede into the interior while their centrosomes remain on the cortex. Following individual free centrosomes through multiple focal planes for 45 min after the injection of aphidicolin reveals that they do not undergo normal modulation of their astral dynamics nor do they undergo multiple rounds of duplication and separation. We conclude that in the absence of normally dividing cortical nuclei many centrosome activities are disrupted and centrosome duplication is extensively delayed. This indicates the presence of a feedback mechanism that creates a dependency relationship between the cortical nuclear cycles and the centrosome cycles.