Mode jumping in the lateral buckling of subsea pipelines

Unburied subsea pipelines under high-temperature conditions tend to relieve their axial compressive stress by forming localised lateral buckles. This phenomenon is traditionally studied under the assumption of a specific lateral deflection profile (mode) consisting of a fixed number of lobes. We study lateral thermal buckling as a genuinely localised buckling phenomenon by applying homoclinic (‘flat’) boundary conditions. By not having to assume a particular buckling mode we are in a position to study transitions between these traditional modes in typical loading sequences. For the lateral resistance we take a realistic nonlinear pipe-soil interaction model for partially embedded pipelines. We find that for soils with appreciable breakout resistance, i.e., nonmonotonicity of the lateral resistance characteristic, sudden jumps between modes may occur. We consider both symmetric and antisymmetric solutions. The latter turn out to require much higher temperature differences between pipe and environment for the jumps to be induced. We carry out a parameter study on the effect of various pipe-soil interaction parameters on this mode jumping. Away from the jumps post-buckling solutions are reasonably well described by the traditional modes whose analytical expressions may be used during preliminary design

Shock sensitivity in the localised buckling of a beam on a nonlinear foundation: The case of a trenched subsea pipeline

We study jump instability phenomena due to external disturbances to an axially loaded beam resting on a nonlinear foundation that provides both lateral and axial resistance. The lateral resistance is of destiffening-restiffening type known to lead to complex localisation phenomena governed by a Maxwell critical load that marks a phase transition to a periodic buckling pattern. For the benefit of having a concrete and realistic example we consider the case of a partially embedded trenched subsea pipeline under thermal loading but our results hold qualitatively for a wide class of problems with non-monotonic lateral resistance. In the absence of axial resistance the pipeline is effectively under a dead compressive load and experiences shock-sensitivity for loads immediately past the Maxwell load, i.e., extreme sensitivity to perturbations as may for instance be caused by irregular fluid flow inside the pipe or landslides. Nonzero axial resistance leads to a coupling of axial and lateral deformation under thermal loading. We define a ‘Maxwell temperature’ beyond which the straight pipeline may snap into a localised buckling mode. Under increasing axial resistance this Maxwell temperature is pushed to higher (safer) values. Shock sensitivity gradually diminishes and becomes less chaotic: jumps become more predictable. We compute minimum energy barriers for escape from pre-buckled to post-buckled states, which, depending on the magnitude of the axial resistance, may be induced by either symmetric, or anti-symmetric or non-symmetric perturbations

Buckling between soft walls: sequential stabilization through contact

Motivated by applications of soft-contact problems such as guidewires used in medical and engineering applications, we consider a compressed rod deforming between two parallel elastic walls. Free elastica buckling modes other than the first are known to be unstable. We find the soft constraining walls to have the effect of sequentially stabilizing higher modes in multiple contacts by a series of bifurcations, in each of which the degree of instability (the index) is decreased by one. Further symmetry-breaking bifurcations in the stabilization process generate solutions with different contact patterns that allow for a classification in terms of binary symbol sequences. In the hard-contact limit, all these bifurcations collapse into highly degenerate ‘contact bifurcations’. For any given wall separation at most a finite number of modes can be stabilized and eventually, under large enough compression, the rod jumps into the inverted straight state. We chart the sequence of events, under increasing compression, leading from the initial straight state in compression to the final straight state in tension, in effect the process of pushing a rod through a cavity. Our results also give new insight into universal features of symmetry-breaking in higher mode elastic deformations. We present this study also as a showcase for a practical approach to stability analysis based on numerical bifurcation theory and without the intimidating mathematical technicalities often accompanying stability analysis in the literature. The method delivers the stability index and can be straightforwardly applied to other elastic stability problems

Use of Antipsychotic Medications and Cholinesterase Inhibitors and the Risk of Falls and Fractures: self-controlled case series

Objective: To evaluate the association between the use of antipsychotic medications and cholinesterase inhibitors, and the risk of falls and fractures in elderly patients with major neurocognitive disorders. / Design: Self-controlled case series / Setting: Taiwan’s National Health Insurance Database / Participants: 15,278 patients who were aged 65 or older, were newly prescribed antipsychotic medications and cholinesterase inhibitors, and suffered an incident fall or fracture between 2006 and 2017. Prescription records of cholinesterase inhibitors were used to confirm the diagnosis of major neurocognitive disorders since all use of cholinesterase inhibitors was subject to review by experts based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition and patients’ scores of Mini-Mental State Examination. We excluded those with schizophrenia and bipolar disorder before the first prescription of cholinesterase inhibitors to ensure that antipsychotic medications were used for neuropsychiatric symptoms of major neurocognitive disorders. / Main outcome measures: We used conditional Poisson regression to derive the incidence rate ratio and the 95% confidence interval for evaluating the association between the risk of falls and fractures and different exposure periods, including cholinesterase inhibitors alone, antipsychotic medications alone, and combination, as compared with the non-exposure period for the same individual. Moreover, we defined a 14-day pre-exposure period before study drug initiation over concerns about confounding by indication. / Results: Compared with the non-exposure period (incidence rate per 100 person-years; 95% confidence interval: 8.30; 8.14 to 8.46), the highest risk of falls and fractures occurred during the pre-exposure period (52.35; 48.46 to 56.47), followed by combination (10.55; 9.98 to 11.14), antipsychotic medications alone (10.34; 9.80 to 10.89), and cholinesterase inhibitors alone (9.41; 8.98 to 9.86). Conclusions: The incidence of falls and fractures was especially high in the pre-exposure period, suggesting that factors other than the study medications, such as underlying diseases, should be taken into consideration when evaluating the association between the risk of falls and fractures, and the use of cholinesterase inhibitors and antipsychotic medications. The exposure periods were also associated with a higher risk of falls and fractures, compared with the non-exposure period, although the magnitude was much lower than during the pre-exposure period. Prevention strategies and close monitoring of the risk of falls are still necessary until there is evidence that patients have regained a steady status

Outer membrane protein folding from an energy landscape perspective

The cell envelope is essential for the survival of Gram-negative bacteria. This specialised membrane is densely packed with outer membrane proteins (OMPs), which perform a variety of functions. How OMPs fold into this crowded environment remains an open question. Here, we review current knowledge about OFMP folding mechanisms in vitro and discuss how the need to fold to a stable native state has shaped their folding energy landscapes. We also highlight the role of chaperones and the β-barrel assembly machinery (BAM) in assisting OMP folding in vivo and discuss proposed mechanisms by which this fascinating machinery may catalyse OMP folding

The rumen microbial metagenome associated with high methane production in cattle

Acknowledgements The Rowett Institute of Nutrition and Health and SRUC are funded by the Rural and Environment Science and Analytical Services Division (RESAS) of the Scottish Government. The project was supported by Defra and the DA funded Agricultural Greenhouse Gas Inventory Research Platform, the Technology Strategy Board (Project No: TP 5903–40240) and the Biotechnology and Biological Sciences Research Council (BBSRC; BB/J004243/1, BB/J004235/1). Our thanks are due to the excellent support staff at the SRUC Beef and Sheep Research Centre, Edinburgh, and to Silvia Ramos Garcia for help in interrogating the data. MW and RR contributed equally to the paper and should be considered as joint last authors.Peer reviewedPublisher PD

Effects of boron doping on the surface morphology and structural imperfections of diamond films

This paper reports the surface morphology and structural imperfection of boron-doped diamond films prepared by microwave plasma enhanced chemical vapor deposition. It was found that boron dopants improved the structural quality of diamond films. The surface morphology consisted mainly of the {111} facets. A significant enhancement of nucleation density and consequent decrease of grain size was observed with the addition of diborane in the gas phase. Raman spectroscopy indicated that, with the introduction of boron dopants, the integrated intensity of the diamond peak at 1332 cm-1 increased relative to the intensity of the non-diamond peak at about 1500 cm-1, and the full-width at half maximum of the 1332 cm-1 peak decreased. In addition, the 1.681 eV (738 nm) photoluminescence peak related to point defects was effectively reduced, or even eliminated by the boron dopants. Finally, transmission electron microscopy studies found that the densities of planar defects (mainly stacking faults and microtwins) also decreased with the boron addition. © 1992