Rigid Bundle Research Articles

Effect of stochastic deformation on the vibration characteristics of a tube bundle in axial flow

Design evaluation of nuclear components using numerical methods has typically been focused on nominal geometries and conditions. In reality, the geometry of reactor components and operating conditions can differ from the design on the drawing table. Increasing understanding and safety of nuclear energy systems requires investigating these more realistic conditions as well. An example is the bow of fuel assemblies, a deformation that occurs after some residence time as a consequence of thermal and irradiation effects. A paradigm shift from purely deterministic simulations toward simulations involving stochastic processes can help to meet this demand.One of the aspects in the design assessment of nuclear reactors is flow-induced vibration (FIV). A lot of experimental effort has already been allocated to FIV phenomena in the past, and more recently also numerical approaches have been applied. However, it was not clear to what extent vibration characteristics would change for a geometry different from the design drawing. In this study the effect of a random bow deformation on the vibration behavior of a flexible tube in a rigid bundle is investigated using fluid–structure interaction simulations. As the (stressless) geometry presumably has a stochastic nature, the modal characteristics should be treated accordingly.For this uncertainty quantification of the modal characteristics, the generalized Polynomial Chaos method was applied. First, only the steady flow through the bundle was considered, without simulating the vibration. This sufficiently reduced the computational cost to apply the Monte Carlo method, which was used to validate the more efficient Polynomial Chaos method. This latter method was found adequate to predict the stochastic modal characteristics of the deformed, flexible tube.

Operational Modal Analysis of a Triangular-Pitch Tube Bundle Subjected to Two-Phase Cross-Flow

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. Electricité de France (EDF) has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi-analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was operated with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions in order to represent the so-called in-plane and out-of-plane vibrations. This paper outlines the experimental results and some detailed physical analysis of some selected points of the experiment series: the response modes are identified by means of operational modal analysis (OMA) (i.e., under unmeasured flow excitation) and presented in terms of frequency, damping, and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluid-elastic instability (FEI).

The Shared Worker: A New Labor Classification for the Sharing Economy

Federal labor law requires employers to give employees a rigid bundle of benefits, including the right to unionize, unemployment insurance, worker’s compensation insurance, health insurance, family medical leave, and more. These benefits are not free – benefits cost about one third of wages – and someone must pay for them. Which of these benefits are worth their cost? This article takes a theoretical approach to that problem and proposes a flexible benefits solution. Labor law developed under a traditional model of work: long-term employees who depended on a single employer to engage in goods-producing work. Few people work that way today. Instead, modern workers are increasingly using multiple technology platforms (such as Uber, Lyft, TaskRabbit, Amazon Flex, DoorDash, Handy, Moonlighting, FLEXABLE, PeoplePerHour, Rover, Snagajob, TaskEasy, Upwork, and many more) to provide short-term service-producing work. Labor laws are a bad fit for this “gig economy.” New legal paradigms are needed. The rigid labor law classification of all workers as either “employees” (who get the entire bundle of benefits) or “independent contractors” (who get none) has led to many lawsuits attempting to re-define who is an “employee” in the gig economy. This issue grows larger as more than one fifth of the workforce is now categorized as an independent contractor. Ironically, the requirement to provide a rigid bundle of benefits to employees has resulted in fewer workers receiving any benefits at all. This article argues for unbundling employment benefits so workers in the gig economy can obtain a more optimal mix of benefits and wages. This article also provides a framework for a more flexible system of employee benefits. This article thus makes three contributions. First, this article demonstrates how a rigid requirement of employment benefits can harm workers. Second, this article shows how labor law should incorporate advances in economic theory that heretofore it generally ignored. Third, this article presents a flexible framework to solve the refractory problem of rigid worker categorization.

A Shish-kebab superstructure in low-crystallinity elastomer nanocomposites: Morphology regulation and load-transfer

In this paper, a regulated morphology of multi-walled carbon nanotube bundles (CNTBs) in olefin block copolymer (OBC) is achieved via a facile method of short-time strong sonication and solution blending. Inside the CNTBs which consist of several to dozens of nanotubes, the nanotubes exhibit a well aligned structure. With the incorporation of CNTBs, a hybrid shish-kebab superstructure is formed that nanotubes in CNTBs form the central stems and OBC crystals form kebabs on the surface of nanotubes. Superior reinforcement is achieved, e.g., the tensile strength and Young’s modulus can be both tripled with 2 wt% CNTB incorporation. A downshift of G'band of CNTBs in nanocomposites in in situ Raman Spectra can be strikingly 10.09 cm−1, presenting remarkably effective load-transfer and leading to significant reinforcement. Additionally, unique morphology of CNTBs and the low compliance of rigid shish-kebab superstructure with large stereo hindrance could also contribute to the reinforcement of OBC/CNTB nanocomposites. In rheological tests, the nanocomposites exhibit quite low rheological percolation threshold of 0.34 wt% and gel point of 0.634 wt% as well as notable difference in terminal behavior in low frequency zone compared to that of neat OBC, revealing that the rigid bundle structure of CNTBs has remarkable effect on the viscoelastic behavior of OBC. Open image in new window

Transcription factor CREB is involved in CaSR-mediated cytoskeleton gene expression.

Our previous studies illustrated that a steady increase of intracellular calcium concentration ([Ca2+]i) was important for maintaining microtubules (MTs) rearrangement in apoptotic cells. However, little is known about the effect of calcium sensing receptor (CaSR)-mediated increase in [Ca2+]i on cytoskeleton gene expression. We examined the impact of taxol or CaSR agonist/antagonist on the regulation of [Ca2+]i concentration, cytoskeleton arrangement, phosphorylated CREB and cytoskeleton gene expressions in HeLa cells with dominant negative plasmid of CREB (PM). This study demonstrated that Gdcl3 (a specific CaSR agonist) evoked a rapid increase of [Ca2+]i, formed a rigid bundle of MTs which surrounded the nucleus and decreased the cytoskeleton gene expressions in HeLa cells. These effects were rescued by addition of NPS2390 (a specific CaSR antagonist). Moreover, CaSR activity affected cytoskeleton gene expression through transcription factor CREB. Histoscores of pCREB immunoreactivity in tissues of cervical adenocarcinoma, renal clear cell carcinoma, and diffuse large B-cell lymphoma were markedly increased compared with non malignant tissue. These data demonstrate, for the first time, that CaSR-mediated increase in [Ca2+]i probably modulate cytoskeleton organization and gene expression via transcription factor.

Assembly of MreB Filaments on Liposome Membranes: A Synthetic Biology Approach

The physical interaction between the cytoskeleton and the cell membrane is essential in defining the morphology of living organisms. In this study, we use a synthetic approach to polymerize bacterial MreB filaments inside phospholipid vesicles. When the proteins MreB and MreC are expressed inside the liposomes, the MreB cytoskeleton structure develops at the inner membrane. Furthermore, when purified MreB is used inside the liposomes, MreB filaments form a 4-10 μm rigid bundle structure and deform the lipid vesicles in physical contact with the vesicle inner membrane. These results indicate that the fibrillation of MreB filaments can take place either in close proximity of deformable lipid membrane or in the presence of associated protein. Our finding might be relevant for the self-assembly of cytoskeleton filaments toward the construction of artificial cell systems.

Experiments and computations of a loosely supported tube in a rigid bundle subjected to single-phase flow

In this paper the problem of computing the nonlinear vibro-impact responses of loosely supported heat-exchanger tubes subjected to fluidelastic coupling forces, as well as to the turbulence excitation from transverse flows, is addressed. Emphasis is on the fluidelastic modeling within a time domain nonlinear framework, as well as on the stabilizing effect of impacts on the fluidelastic coupling forces. Theoretical computations of the linear and vibro-impacting regimes of a flow-excited flexible cantilever test tube, within a rigid 3×5 square bundle, are based on the experimentally identified fluidelastic coupling force coefficients and turbulence spectrum. Computations are then compared with the experimental vibratory responses, enabling a full validation of the modeling approach. Furthermore, interesting conclusions are drawn, concerning (a) the energy balance between sources and sinks, for a vibro-impacting tube subjected to fluidelastic forces and (b) the dependence of the vibration response frequency on impacts at the loose supports, and their effect on the nonlinear restabilization of fluidelastically unstable tubes. Details on the following aspects are reported in the paper: (1) numerical modeling of the fluidelastic coupling forces for the time domain computations; (2) experimental identification of the fluidelastic coupling coefficients; (3) computations and experiments of both linear and vibro-impacting responses under the combined action of turbulence and fluidelastic coupling and (4) energy aspects of the vibro-impacting fluidelastically coupled tube responses.

Structure of the acrosomal bundle, a biological machine, at 9.5 Å resolution

In the unactivated Limulus sperm, a 60 μm-long bundle of actin filaments crosslinked by scruin is bent and twisted into a coil around the base of the nucleus. At fertilization the bundle uncoils and fully extends in five seconds to support a finger of membrane, the acrosomal process. This biological spring is powered by stored elastic energy and does not require the action of motor proteins or actin polymerization. Our 9.5 A electron cryomicroscopic structure of the extended bundle [1] shows that twist, tilt, and rotation of actin-scruin subunits deviate widely from a standard F-actin filament. This deviation appears to be related to the packing requirements of the scruin cross-linkers. The structural organization allows filaments to pack into a highly ordered and rigid bundle in the extended state, but also suggests a mechanism for storing and releasing energy between the coiled and extended states.

Structure of the acrosomal bundle.

In the unactivated Limulus sperm, a 60- micro m-long bundle of actin filaments crosslinked by the protein scruin is bent and twisted into a coil around the base of the nucleus. At fertilization, the bundle uncoils and fully extends in five seconds to support a finger of membrane known as the acrosomal process. This biological spring is powered by stored elastic energy and does not require the action of motor proteins or actin polymerization. In a 9.5-A electron cryomicroscopic structure of the extended bundle, we show that twist, tilt and rotation of actin-scruin subunits deviate widely from a 'standard' F-actin filament. This variability in structural organization allows filaments to pack into a highly ordered and rigid bundle in the extended state and suggests a mechanism for storing and releasing energy between coiled and extended states without disassembly.

Coherent hollow-core waveguide bundles for infrared imaging

Coherent IR fiber optic bundles for use in IR imaging from 2 to 12 µm are fabricated from rigid hollow-glass waveguide arrays. The bore of each hollow glass tube in the bundle is coated with thin films of metallic Ag followed by AgI for enhanced reflectivity. The coating of the rigid bundle is done using liquid phase chemistry techniques applied to all tubes simultaneously. The hollow-glass arrays are composed of up to 900 individual tubes with bore sizes as small as 50 µm. Several rigid hollow-core arrays are used to transmit an IR image of a small loop of hot wire and a sample of tissue heated by a CO2 laser.

Active Vibration Control for the Measurement of Fluidelastic Effects

A new method based on active vibration control is proposed to investigate fluidelastic coupling effects beyond fluidelastic instability. This active control method allows to extend the range of flow velocity explored for single input-single output control systems. The method is applied on a flexible tube inserted in a rigid bundle in water and air-water cross-flows. This structure becomes unstable for high flow velocities, fluidelastic forces then causing the damping of the fluid-structure system to fall towards zero. The active control method allows to carry out tests beyond the fluidelastic instability. The flow velocity range explored is doubled in two-phase flow.

Design considerations and initial performance of a 1.2 cm/sup 2/ beta imaging intra-operative probe

A novel small area beta (/spl beta//sup /spl plusmn//) detector is under development for nuclear emission imaging of surgically exposed, radiolabeled tumor beds. The imaging device front-end consists of a 0.5 mm thick by 1.25 cm diameter CaF/sub 2/(Eu) scintillator disk coupled to a rigid bundle of 2 mm diameter double clad optical fibers through a polystyrene light diffuser. The detector area (1.2 cm/sup 2/) was determined by the requirement of introducing the probe into small cavities, e.g. during neuro-surgical lesion resection, but large enough to produce images of clinical significance. Flexible back-end optical fibers (1.9 m long) were coupled to the front-end components allowing /spl sim/75 photo-electrons to be detected for mean beta energies of 250 keV, indicating that sufficient signal can be obtained with clinical beta emitters (e.g. /sup 18/F, /sup 131/I). The long flexible fibers guide the scintillation light to a Philips XP1700 series, fiber optic faceplate, Multi-Channel PMT. The parallel MC-PMT outputs are fed into a variable gain, charge divider network and an i-V pre-amplifier/line driver network, whose resulting four outputs are digitized and histogrammed with standard Anger positioning logic. The various components in the imaging chain were evaluated and optimized by both simulations and measurements. Line spread functions measured in the 10.8 mm FOV were 0.50 mm /spl plusmn/0.038 mm and 0.55 mm /spl plusmn/0.065 mm FWHM in X and Y, respectively. A 20% variation in pulse height and minimal variation in spatial resolution was observed. The differential image uniformity was measured to be /spl plusmn/15.6% with /spl sim/150 cts/pixel. Preliminary images show excellent reproduction of phantom activity distributions.

Distribution and Ultrastructure of Ciliated Sensory Receptors in the Posterior Mantle Epithelium of Dentalium rectius (Mollusca, Scaphopoda)

AbstractThe scaphopod mantle cavity opens posteriorly via the pavilion, a siphon‐like extension of the posterior mantle through which the respiratory currents pass. The pavilion was examined for ciliated sensory cells in Dentalium rectius Carpenter, 1865, using scanning and transmission electron micropscopy. Three types of sensory receptor were distinguished on the basis of number, length and ultrastructure of the associated cilia. Receptors with 2–5 cilia of ˜ 1.7 μm length lined the pavilion edge. A second type, possessing 1–2 cilia, ˜ 8.2 μm in length, was found throughout the internal and on part of the external surface of the pavilion. The third receptor type consisted of a rigid bundle of 16–40 cilia with a length of ˜ 14.4 μm, and was present close to the periphery and at the base of the pavilion near the entrance to the mantle cavity. The structure and distribution of these cells are similar to peripheral chemo‐ and mechanoreceptors which sample respiratory currents and the surrounding environment in other molluscs, but they may assume a greater functional significance in scaphopods due to the absence of an osphradium in this class.

Illuminating Manuscripts

ILLUMINATING MANUSCRIPTS / Glover Davis Like unicorn and dragon eagle soon may be an ornate symbol in a book. Hung from a column, wings will be a rune whose twisted lines, though smeared with carbon, hook light swimming potencies in channels shook by hand through leaves which raise a cottonwood— first letter in a lost genetic code. So when a clavicle began to rise with every gust from panes whose leaves and glass spilled through the seething curtains taped with gauze, my riffling fingers were like blades of grass against the place where dreaming feathers mass. The bulging skin implied with a wing of stone a sculptor's chisle loosened from the bone. Red cloth would scarve the cries of predators; the throbbing wound the world had come to be. But sudden blasts unbolted the french doors. Lightning illuminated a struck tree. Brocaded branches carved the roiling sky with capitals metallic leaves efface by constant spill of pieces cut like lace. The manuscript of leaves contained no reasons for an eagle's tumbling to the floor, his white hood daubed by spotting fingers red as suns. He had one eye, and when I spread the tight coil of a wing, the eye dusted with light spasmodically pulsed, as though the light were breath melted from mirrors just before his death. I knew I must not let the eagle die. I knew his powers—transcribed to letters spelt in loops and swirls across a brightening sky— 178 · The Missouri Review were trails of chalk the wind and hot sun melt. A blackened eye was gushing as I knelt and pressed the rigid bundle to my chest, hoping a heart would beat through either breast. Glover Davis The Missouri Review · 179 ...