Large Blockages Research Articles

Single Molecular Nanopores as a Label-Free Method for Homogeneous Conformation Investigation and Anti-Interference Molecular Analysis

In this paper, we propose a "reciprocal strategy" that, on the one hand, explores the ability of solid-state nanopores in a homogeneous high-fidelity characterization of nucleic acid assembly and, on the other hand, the formed nucleic acid assembly with a large size serves as an amplifier to provide a highly distinguished and anti-interference signal for molecular sensing. Four-hairpin hybridization chain reaction (HCR) with G-rich tail tags is taken as the proof-of-concept demonstration. G-rich tail tags are commonly used to form G-quadruplex signal probes on the side chain of HCR duplex concatemers. When such G-tailed HCR concatemers translocate the nanopore, abnormal, much higher nanopore signals over normal duplexes can be observed. Combined with atomic force microscopy, we reveal the G-rich tail may easily induce the "intermolecular interaction" between HCR concatemers to form "branched assembly structure (BAS)". To the best of our knowledge, this is the first evidence for the formation BAS of the G tailed HCR concatemers in a homogeneous solution. Systematic nanopore measurements further suggest the formation of these BASs is closely related to the types of salt ions, the amount of G, the concentration of substrate hairpins, the reaction time, and so forth. Under optimized conditions, these BASs can be grown to just the right size without being too large to block the pores, while producing a current 14 times that of conventional double-stranded chains. Here, these very abnormal large current blockages have, in turn, been taken as an anti-interference signal indicator for small targets in order to defend the high noises resulting from co-existing big species (e.g., enzymes or other long double-stranded DNA).

Reverse Translation to Develop Post-stroke Therapeutic Interventions during Mechanical Thrombectomy: Lessons from the BACTRAC Trial.

The majority of strokes, approximately 87%, are ischemic in etiology with the remaining hemorrhagic in origin. Emergent large vessel occlusions (ELVOs) are a subtype of ischemic stroke accounting for approximately 30-40% of acute large vessel blockages. Treatment for ELVOs focuses on recanalization of the occluded vessel by time-sensitive administration of tissue plasminogen activator (tPA) or thrombus removal using mechanical thrombectomy. Although a great deal of time and resources have focused on translational stroke research, little progress has been made in the area of identifying additional new treatments for stroke. Translational limitations include difficulty simulating human comorbid conditions in animal models, as well as the temporal nature of stroke pathology. The Blood And Clot Thrombectomy Registry And Collaboration represents an ongoing tissue registry for thrombectomy patients and includes collection of intracranial arterial blood, systemic arterial blood, thrombi, as well as a series of clinical and radiographic data points for analysis. This chapter will explore the methodologies employed and results obtained from studying BACTRAC-derived human biological specimens and how they can inform translational experimental design in animal studies.

Unstable Transients Affecting Flow Assurance during Hydraulic Transportation of Granular Two-Phase Slurries

Hydraulic two-phase transport applied in the dredging, mining, and deep-sea mining industries involves the transportation of sand, gravel, polymetallic nodules, or other particulate tailings as a solids phase and water as a liquid phase. Regardless of the type or size of the granular material, the slurry flow is always subject to transient behavior. Most transient behavior can be attributed to the centrifugal pump as variations in pump pressure and mixture velocity over time, but transients can also be caused by microscopic slurry mechanisms, specifically the amplification of density waves in a pipeline. Density wave amplification in horizontal pipelines at mixture velocities just above the deposition limit velocity was reported and researched in the 1990s. New experiments showing a density wave amplification in a system with combined vertical and horizontal pipelines and at mixture velocities far above the deposition limit suggest that another type of density wave amplification mechanism exists. The newly proposed density wave amplification mechanism is hypothesized to be caused by a change in average particle velocity as the slurry flows from a vertical pipe into a horizontal pipe. Density waves that grow too large cause system blockages or possibly a failure of the pump drive. This article considers centrifugal pump–induced transients and density wave amplification effects separately and how these effects influence each other. Three case studies showing density wave amplification are analyzed, one from the literature and two from new data sets. Furthermore, the causes of these transients are discussed, and where possible, solutions are proposed to avoid these undesirable instabilities.

Observing Transient Bipolar Electrochemical Coupling on Single Nanoparticles Translocating through a Nanopore.

We report the observation of transient bipolar electrochemical coupling on freely moving 40 nm silver nanoparticles. The use of an asymmetric nanoelectrochemical environment at the nanopore orifice, for example, an acid inside the pipette and halide ions in the bulk, enabled us to observe unusually large current blockages of single Ag nanoparticles. We attribute these current blockages to the formation of H2 nanobubbles on the surface of Ag nanoparticles due to the coupled faradaic reactions, in which the reduction of protons and water is coupled to the oxidation of Ag and water under potentials higher than 1 V. The appearance of large current blockages was strongly dependent on the applied voltage and the choice of anions in the bulk solution. The correlation between large current blockages with the oxidation of Ag nanoparticles and their nanopore translocation was further supported by simultaneous fluorescence and electric recordings. This study demonstrates that transient bipolar electrochemistry can take place on small metal nanoparticles below 50 nm when they pass through nanopores where the electric field is highly localized. The use of a nanopore and the resistive-pulse sensing method to study transient bipolar electrochemistry of nanoparticles may be extended to future studies in ultrafast electrochemistry, nanocatalyst screening, and gas nucleation on nanoparticles.

Investigation of the Flow Characteristics of Methane Hydrate Slurries with Low Flow Rates

Gas hydrate blockage in pipelines during offshore production becomes a major problem with increasing water depth. In this work, a series of experiments on gas hydrate formation in a flow loop was performed with low flow rates of 0.33, 0.66, and 0.88 m/s; the effects of the initial subcooling, flow rate, pressure, and morphology were investigated for methane hydrate formation in the flow loop. The results indicate that the differential pressure drop (ΔP) across two ends of the horizontal straight pipe increases with increasing hydrate concentration at the early stage of gas hydrate formation. When the flow rates of hydrate fluid are low, the higher the subcooling is, the faster the transition of the hydrates macrostructures. Gas hydrates can agglomerate, and sludge hydrates appear at subcoolings of 6.5 and 8.5 °C. The difference between the ΔP values at different flow rates is small, and there is no obvious influence of the flow rates on ΔP. Three hydrate macrostructures were observed: slurry-like, sludge-like, and their transition. When the initial pressure is 8.0 MPa, large methane hydrate blockages appear at the gas hydrate concentration of approximately 7%. Based on the gas–liquid two-phase flow model, a correlation between the gas hydrate concentration and the value of ΔP is also presented. These results can enrich the kinetic data of gas hydrate formation and agglomeration and provide guidance for oil and gas transportation in pipelines.

A preliminary study of the failure mechanisms of cascading landslide dams

Landslide dams commonly form when mass earth or rock movements reach a river channel and cause a complete or partial blockage of the channel. Intense rainfalls can induce upstream flows along a sloping channel that significantly affect downstream landslide dams. If a series of landslide dams are collapsed by incoming mountain torrents (induced by intense rainfall), large debris flows can form in a very short period. Furthermore, the failure of these dams can amplify the magnitude and scale of debris flows in the flow direction. The catastrophic debris flows that occurred in Zhouqu County, China on 8 August 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies. Incorporating the role of outburst floods associated with the complete or partial failure of landslide dams is an interesting problem usually beyond the scope of analysis because of the inherent modeling complexity. To understand the cascading failure modes of a series of landslide dams, and the dynamic effect these failures have on the enlargement of debris flow scales, experimental tests are conducted in sloping channels mimicking field conditions, with the modeled landslide dams distributed along a sloping channel and crushed by different upstream flows. The failure modes of three different cascades of landslide dams fully or partially blocking a channel river are parametrically studied. This study illustrates that upstream flows can induce a cascading failure of the landslide dams along a channel. Overtopping is the primary failure mechanism, while piping and erosion can also induce failures for different constructed landslide dams. A cascading failure of landslide dams causes a gradually increasing flow velocity and discharge of the front flow, resulting in an increase in both diameter and percentage of the entrained coarse particles. Furthermore, large landslide blockages can act to enhance the efficiency of river incision, or conversely to induce aggradation of fluvial sediments, depending on the blockage factor of the landslide dams and upstream discharge.

SAS4A analysis on hypothetical total instantaneous flow blockage in SFRs based on in-pile experiments

Local fault (LF) has been historically considered as one of the possible causes of severe accidents in sodium-cooled fast reactors (SFRs). Safety assessments on the consequences of three major LF initiators, adventitious-fuel-pin-failures, local over-powers and large flow blockages, have already been performed for the Japanese prototype fast breeder reactor (Monju) and resulted in limited damage within a fuel subassembly. Although the frequency of hypothetical total instantaneous flow blockage at the coolant inlet of a fuel subassembly (HTIB) is negligible, in-pile experiments on this event have been performed because it gives the most severe consequences among the abovementioned LF initiators. Therefore the most rapid damage propagation assumption was newly proposed in this study based on past experiments, and a safety evaluation was performed on the consequences of HTIB in Monju using the SAS4A code, additionally validated by an in-pile experiment specifically on the HTIB-related phenomena. It was shown through the evaluation that the consequences of HTIB were much less severe than that of the unprotected loss of flow (ULOF) events which represent the most severe accidents in Monju. Therefore it was concluded that all the consequences of LFs in Monju can be found among the consequences of ULOF. This evaluation method would be also applicable to enveloping safety assessments of LFs in generic SFRs.

A CFD analysis of flow blockage phenomena in ALFRED LFR demo fuel assembly

A CFD study was carried out on fluid flow and heat transfer in the Lead-cooled Fuel Pin Bundle of the ALFRED LFR DEMO.In the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel sub-assembly is considered one of the main issues to be addressed and the most important and realistic accident for LFR fuel assembly. The present paper is a first step toward a detailed analysis of such phenomena, and a CFD model and approach are presented to have a detailed thermo-fluid dynamic picture in the case of blockage. In particular the closed hexagonal, grid-spaced fuel assembly of the LFR ALFRED was modeled and computed. At this stage, the details of the spacer grids were not included, but a conservative analysis has been carried out based on the current main geometrical and physical features. Reactivity feedback, as well as axial power profile, were not included in this analysis. Results indicate that critical conditions, with clad temperatures around ∼900°C, are reached with blockage larger than 30% in terms of area fraction.Two main effects can be distinguished: a local effect in the wake/recirculation region downstream the blockage and a global effect due to the lower mass flow rate in the blocked subchannels; the former effect gives rise to a temperature peak behind the blockage and it is dominant for large blockages (>20%), while the latter effect determines a temperature peak at the end of the active region and it is dominant for small blockages (<10%). The blockage area was placed at the beginning of the active region, so that both overmentioned phenomena can fully take place. The mass flow rate at the different degree of blockage was imposed from preliminary system code simulations.Transient analyses with fully resolved SST-omega turbulence model were carried out and results indicate that a blockage of ∼15% (in terms of blocked area) leads to a maximum clad temperature around 800°C, and this condition is reached in a characteristic time of 3–4s without overshoot. Local clad temperatures around 1000°C can be reached for blockages of 30% or more.CFD simulations indicate that blockages >15% could be detected by putting some thermocouples in the plenum region of the FA.

Improvement of Core Modeling in ICARE/CATHARE: Application to the Calculation of a Six-Inch-Break LOCA Leading to a Severely Degraded Situation

In order to analyze the course of a hypothetical severe accident, the French “Institut de Radioprotection et de Sûreté Nucléaire” in the last decade has developed computer codes that have been extensively used for supporting the Level 2 Probabilistic Safety Assessment (PSA2) and, in general, for the safety analysis of French pressurized water reactors (PWRs).In particular, the computer code ICARE/CATHARE V1 is a tool that has been widely validated and intensively used within the framework of the PSA2 of the 900-MW(electric) French PWR. This code has been tested on many accident scenarios, and the results obtained have been considered to be satisfactory and reliable up to the end of the early degradation phase. But, severe accidents in PWRs are characterized by a continuous evolution of the core geometry due to chemical reactions, melting, and mechanical failure of the rods and other structures. These local variations of the porosity and other parameters lead to multidimensional flows and heat transfers. So, the lack of a multidimensional two-phase thermal-hydraulic model appeared to be prejudicial to achieve best-estimate reactor studies with ICARE/CATHARE V1 in the case of large core blockages and/or in the case of large cavity appearance. In accordance, a full multidimensional modeling (covering both the fluid flow and the corium behavior) was developed and introduced in a new ICARE/CATHARE version referenced as V2, which includes two options for the thermal-hydraulic modeling: either one-dimensional (1D) or two-dimensional (2D).The first part of this paper demonstrates that without activating the new V2 models, ICARE/CATHARE V2(1D) is able to reproduce the results obtained with ICARE/CATHARE V1 on the basis of a 6-in.-break loss-of-coolant accident. Then, in order to illustrate some of the new V2 modeling improvements, the last part is focused on the results obtained with ICARE/CATHARE V2(2D), and a preliminary comparison is made with ICARE/CATHARE V2(1D).This 1D-2D comparison points out in particular the important role that could be played in the course of a severe accident by the multidimensional flow pattern.

A conceptual model of depositional, rather than erosional, tidal channel development in the rapidly prograding Skagit River Delta (Washington, USA)

AbstractThe origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind tidal channel origin and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary channels gradually narrowed and finally closed at the upstream end to form a blind tidal channel, or at mid‐length to form two blind tidal channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and channel lengthening, coupled with large woody debris blockages. Blind tidal channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind tidal channels. The smallest observed distributary‐derived modern blind tidal channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a channel is obstructed and isolated from distributary flow, only tidal flow remains and channel persistence becomes a function of tidal prism and tidal or wind/wave erosion. In rapidly prograding systems like the Skagit, blind tidal channel networks are probably inherited from the antecedent distributary network. Examination of large‐scale channel network geometry of such systems should therefore consider distributaries and blind tidal channels part of a common channel network and not entirely distinct elements of the system. Finally, managers of tidal habitat restoration projects generally assume an erosional model of tidal channel development. However, under circumstances conducive to progradation, depositional channel development may prevail instead. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Characteristics of Constrained Cavitating Bluff Body Wakes

The wake characteristics of constrained, cavitating two‐dimensional bluff bodies are studied over a large range of blockage. Prismatic sources with fixed separating points are chosen to reduce or eliminate Reynolds number effects. The effect of blockage on the geometrical characteristics of the wake such as the length and width of cavity are obtained. The frequency of cavity pressure pulsations, the pressure histograms, and the mean static pressure distributions along the wake axis are also determined at various cavitating conditions. Efforts are made to obtain the proper velocity and length scales to form the Strouhal numbers to absorb blockage effects. At very large blockages, the generation of small eddies in the shear layers accompanied by a reduction or elimination of Karman vortex street is noticed. Limited studies related to the wake characteristics of a circular source at a moderate blockage of 33% are also reported.

Transient Destratification in a Rectangular Enclosure

An experimental study of transient destratification in a rectangular air-filled enclosure is described. The test cell, which is 1 m high, 0.5 m wide, and 0.25 m deep, is made of plexiglass with a variety of side and bottom thermal boundary conditions. The initial vertical stratification is 30°C. A number of transient tests are reported in which a destabilizing heat source is introduced after the initial stratification. Temperature maps of the middepth plane are recorded and analyzed. Basic enclosure destratification dynamics are described in terms of developing thermal and flow fields. Separate effects of horizontal partitioning, stabilizing side heating, and asymmetric heating are studied. Certain large fractional horizontal blockages are shown to enhance destratification, while side heating is demonstrated to be a stablizing effect that produces a steady-state inversion.

On local blockage formation in sodium cooled reactors

For LMFBR safety considerations the formation of local blockages in the reactor core is investigated since years. A summary of experimental and theoretical results is given considering e.g. granulate material sources, transport phenomena, geometrical data and technological concepts influencing blockage deposition. The experimental results show clearly that for safety relevant blockages in fuel element subchannels a sufficient mass of solid particles of the right grain size is necessary to be accumulated in a few subchannels. Transport by the primary coolant through the whole pool or loop type reactor and distribution in the lower core plenum are not expected to lead to non-fuel blockages. For fuel particle blockages canning defects have to occur first. The experiments show that in this case wire wrapping has some advantages for coolability compared to spacer grids. But here also a lot of undetected material is necessary. Assuming a high quality standard for fuel element production and e.g. a sensitive DND-system for early failure detection with subsequent removal of defect fuel elements the risk of sufficiently large local blockages with following incidental situations is very low.

Flow-Induced Forces on a Cylinder for Different Wall Confinements at High Reynolds Numbers (3.5×105)&lt;Re&lt;(1.2×106)

The nearness of a cylinder to a wall has an important effect on the flow-induced forces exerted on that cylinder, particularly when the cylinder is relatively large compared to the cross section of the flow channel. This paper describes an investigation of wall interference effects that occur when crossflow-induced forces are exerted on circular cylinders with moderately large blockages (d/h = 0.2 to 0.33) at high Reynolds numbers (3.5 × 105 – 1.2 × 106). The results show that, within the range studied, the gap flow velocity is the correct flow velocity to compensate for wall interference effects. The data reported here represent the first available information on experimental cross-flow-induced forces at such high Reynolds numbers using water as a flow medium.