Disk Sides Research Articles

Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

Abstract The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (∼1–20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

Reduced order modelling of full-span rotating stall for the flow control simulation of axial compressors

A 2D mean-radius reduction of the flow inside an axial compressor is proposed here as basic model for long-term simulations of active control strategies. In fact, research on active control of compressor instabilities is still based on the 0-D lumped volume approach of Moore and Greitzer, 1 , 2 with enhancements, or on one-dimensional axial flow models. In the present work, the dynamics of the compressor flow instabilities is represented in both the axial and peripheral directions. Although this intermediate-level analysis cannot capture fully 3D aspects of rotating stall inception and the part-span stall, it has shown to include a wide variety of details with respect to simpler models, while it still retains computational requirements that allow for the long-term simulation of an entire compression system. In this framework, the paper focuses on the derivation of a flow model that can mimic the onset and the development of the instabilities leading the compressor to full-span rotating stall. The flow inside the compressor is solved by means of two-dimensional Euler equations whereas the effects of blade rows are modelled by quasi-steady actuator disks. The characteristic-based flux treatment on the actuator disk sides ensures a correct propagation of the wave signals. Therefore, flow perturbations can be followed until they lead to instabilities within the flow field. Both small and large amplitude disturbances are treated. Aerodynamic instabilities are numerically investigated and compared to experimental results. The numerical technique has been validated against available experiments on NASA Rotor 1B and against numerical and experimental data on the throttling of the BR710 multi-stage compressor rig.

Application and validation of a simplified numerical approach for the estimation of windage power losses in spur gears

In this paper a computational fluid dynamics (CFD) code is applied to three-dimensional simulations of windage power loss generated by spur gears rotating in air. Emphasis is placed on the simplification which can be made in the numerical approach in order to gain cost and time needed for reaching a converged solution when using both fine mesh and important angular velocity. It appears that the similarity of the flows which are observed in the vicinity of both gear and disk sides is helpful. It is finally possible to compute the flow pattern near the teeth without simulating the contribution of the sides when appropriate boundary conditions are applied at the inlet of a truncated computational domain. The predictions of windage power losses using this original method are satisfying.

Heat Transfer for the Blade of a Cooled Stage and One-Half High-Pressure Turbine—Part I: Influence of Cooling Variation

Heat-flux measurements are presented for a one-and-one-half stage high-pressure turbine operating at design-corrected conditions with modulated cooling flows in the presence of different inlet temperature profiles. Coolant is supplied from a heavily film-cooled vane and the purge cavity (between the rotor disk and the upstream vane) but not from the rotor blades, which are solid metal. Thin-film heat-flux gauges are located on the uncooled blade pressure and suction surface (at multiple span locations), on the blade tip, on the blade platform, and on the disk and vane sides of the purge cavity. These measurements provide a comprehensive picture of the effect of varying cooling flow rates on surface heat transfer to the turbine blade for uniform and radial inlet temperature profiles. Part I of this paper examines the macroscopic influence of varying all cooling flows together, while Part II investigates the individual regions of influence of the vane outer and purge cooling circuits in more detail. The heat-flux gauges are able to track the cooling flow over the suction surface of the airfoil as it wraps upwards along the base of the airfoil for the uniform vane inlet temperature profile. A similar comparison for the radial profile shows the same coolant behavior but with less pronounced changes. From these comparisons, it is clear that cooling impacts each temperature profile similarly. Nearly all of the cooling influence is limited to the blade suction surface, but small changes are observed for the pressure surface. In addition to the cooling study, a novel method of calculating the adiabatic wall temperature is demonstrated. The derived adiabatic wall temperature distribution shows very similar trends to the Stanton number distribution on the blade.

Computer hardware for radiologists: Part 2

Computers are an integral part of modern radiology equipment. In the first half of this two-part article, we dwelt upon some fundamental concepts regarding computer hardware, covering components like motherboard, central processing unit (CPU), chipset, random access memory (RAM), and memory modules. In this article, we describe the remaining computer hardware components that are of relevance to radiology. “Storage drive” is a term describing a “memory” hardware used to store data for later retrieval. Commonly used storage drives are hard drives, floppy drives, optical drives, flash drives, and network drives. The capacity of a hard drive is dependent on many factors, including the number of disk sides, number of tracks per side, number of sectors on each track, and the amount of data that can be stored in each sector. “Drive interfaces” connect hard drives and optical drives to a computer. The connections of such drives require both a power cable and a data cable. The four most popular “input/output devices” used commonly with computers are the printer, monitor, mouse, and keyboard. The “bus” is a built-in electronic signal pathway in the motherboard to permit efficient and uninterrupted data transfer. A motherboard can have several buses, including the system bus, the PCI express bus, the PCI bus, the AGP bus, and the (outdated) ISA bus. “Ports” are the location at which external devices are connected to a computer motherboard. All commonly used peripheral devices, such as printers, scanners, and portable drives, need ports. A working knowledge of computers is necessary for the radiologist if the workflow is to realize its full potential and, besides, this knowledge will prepare the radiologist for the coming innovations in the ‘ever increasing’ digital future.

Erratum to: Analyzing and dating the structure of the Phaistos Disk

The original version of this article unfortunately contains mistakes in the second section concerning the disk sides. The first line in the fourth paragraph should read: The spiral of both sides has 18 boxes with a small but important box on side A right after the 18th box counted from the center. The sixth paragraph should read: This structure is not visible on first glance, e.g., both box groups, the inner spiral and the outer rim, were often identified as one contiguous group, as can be seen in the literature, where the side A’s box names ranged from A01not stopping at A18—to A30; obviously, the short break at A18 is overlooked, and the possibility to identify a Saros cycle is missed.

Peculiarities of Pyroelectric Resonance–Antiresonance Phenomena in PZT Ceramics

The pyroelectric characteristics of lead–zirconate–titanate (PZT) ceramics of composition near the morphotropic phase boundary were studied by the photothermomodulation method. The frequency spectra of the amplitude and phase of pyroelectric response in the current and voltage modes were transformed into thermowave profiles. The asymmetry of thickness profiles of the pyroactivity distribution and its reversal under reversing poling voltage polarity were revealed. Attention has been concentrated on elucidation of the peculiarities of pyroelectric resonance–antiresonance (PyRAR) and inverse antiresonance–resonance (PyARR) sequences observed in the 25–35 kHz range thermowave excitation of flexural mode thermomechanical vibrations induced by periodical thermal stresses in the undersurface layer of PZT disks. External voltage‐controllable reversible inversion of the sequence PyRAR to PyARR under IR‐beam probing of the opposite disk sides, being at different polarities of poling voltage, was found. The connection between poling voltage polarity, the shape of the thermowave profile of pyroelectric parameters, and the inversion of Py (RAR–ARR) sequence were ascertained. The results are compared with those observed earlier for edge‐fixed PVDF and P(VDF/TrFE) copolymer films and discussed in regard to highly sensitive pyroelectric detectors.

The Infrared Emission of Circumstellar Envelopes, Dark Silhouettes, and Photoionized Disks in HiiRegions

We have modeled the infrared (IR) spectral energy distribution (SED) of circumstellar disks embedded in a H II region and photoevaporated by the external ultraviolet radiation. The model applies to the photoevaporated disks (proplyds) in the Orion Nebula, most of them illuminated by the O6.5 star θ1 Ori C. First we calculate the IR emission of a pre-main-sequence star surrounded by a dusty globule that is immersed within an H II region. The globule is assumed to be spherical, homogeneous, optically thin at IR wavelengths, and photoevaporated according to the Dyson model. Second, we consider the IR emission of a disk directly exposed to the nebular environment. The reprocessing disk is passive and treated according to the Chiang & Goldreich model. We improve over the Chiang & Goldreich treatment by tracing the propagation of the various radiative fluxes (from the star exciting the H II region, nebular, and grazing from the disk central star) through the disk superheated atmosphere. Since the opposite disk sides receive different amounts of radiation, the flaring angle and the surface temperature distributions are different, resulting in well-distinguished SEDs for the two disk faces. Finally, we combine the globule and disk models to estimate the IR emission of proplyds. The energy input from the central star and the nebular environment increase the disk flaring angle, and therefore also the amount of stellar radiation intercepted by the disk. The relative intensity of the disk versus envelope emission varies with the tilt angle relative to the directions of θ1 Ori C and the Earth. We explore the dependence of the SEDs upon the tilt angle with respect to the Earth, the distance from θ1 Ori C, the size on the envelope, the inner disk radius, and the temperature of the central star. The resulting SEDs are characterized by a broad peak of emission at 30-60 μm and are in general significantly different from those of isolated disks in low-mass star-forming regions like Taurus-Auriga. Our model indicates that in the presence of an external radiation field, relatively evolved Class 2 objects may display a SED peaking at mid-IR and far-IR wavelengths. Also, the model can account for the strong mid-IR excess we have recently detected at 10 μm from embedded disks in the Orion Nebula.

Three New Combinations and a New Name in Chinese Boraginaceae

The new combinations Lappula karelinii (Fischer & Meyer) R. Kamelin, Lindelofia stylosa (Karelin & Kirilow) Brand subsp. pterocarpa (Ruprecht) R. Kamelin, and Onosma setosa Ledebour subsp. transrhymnense (Klokov ex M. Popov) Kamelin are made, and the new name 0. liui R. Kamelin & T. Popova is proposed. The revision of the Boraginaceae for the Flora of China is in progress, and this study has shown that four nomenclatural adjustments are needed in the genera Lindelofia, Lappula, and Onosma. These changes are proposed here to make the names available for the forthcoming volume 16 of the Flora. Lappula karelinii (Fischer & Meyer) R. Kamelin, comb. nov. Basionym: Echinospermum karelinii Fischer & Meyer, Ind. Sem. Hort. Petrop. 11: 67. 1845. TYPE: [Kazakhstan]. Soongaria. Grown at St. Petersburg Botanical Garden by C. A. Meyer in 1845 from seed collected by G. Karelin (holotype, LE). Lappula xinjiangensis C. Y. Yang ex C. J. Wang, Bull. Bot. Res. (Harbin) 1(4): 84. 1981, syn. nov. TYPE: China. Xinjiang: Burqin Xian, Ertix He, alt. 400 m, 28 May 1972, C. Y. Yang A-720042 (holotype, XJA). Lappula karelinii was treated by Popov (1953) as a variant of L. tenuis (Ledebour) Giirke, but the latter has a white tuberculate disk and nutlet sides instead of the smooth and polished disk and nutlets characteristic of L. karelinii. Wang (1981) described L. xinjiangensis C. Y. Yang ex C. J. Wang, but this plant is clearly conspecific with L. karelinii. Lindelofia stylosa (Karelin & Kirilow) Brand subsp. pterocarpa (Ruprecht) R. Kamelin, comb. et stat. nov. Basionym: Solenanthus nigricans Schrenk var. pterocarpus Ruprecht, Mem. Acad. Imp. Sci. St. Petersbourg, ser. 7, 14(4): 62. 1869. TYPE: [Kyrgyzstan]. TianShan, Dshaman-daban Pass, 19 July 1857, Osten-Sacken s.n. (holotype, LE). Subspecies pterocarpa was treated by Popov (1953) as a distinct species, although he argued that it probably deserves only a subordinate rank. It differs from subspecies stylosa by its dentate narrow wing on the nutlet margin. In contrast, subspecies stylosa has small, anchorlike prickles along the nutlet margin. Onosma liui R. Kamelin & T. Popova, nom. nov. Replaced name: Onosma strigosum Y. L. Liu, Acta Phytotax. Sin. 18: 65. 1980, non 0. strigosum Steven, Bull. Soc. Nat. Moscou 24: 594. 1851. TYPE: China. Sichuan: Rangtang, alt. 3,400 m, July 1975, no collector name, #9355 (holotype, CDBI). Onosma setosa Ledebour subsp. transrhymnense (Klokov ex M. Popov) Kamelin, comb. et stat. nov. Basionym: Onosma transrhymnense Klokov ex M. Popov, Spisok Rast. Gerb. Fl. SSSR 12: #3564. 1953. TYPE: [Kazakhstan]. Between Chernojarskoe and Pavlodar, on Irtysch River, 2 June 1890, P. Schmidt s.n. (holotype, LE). This subspecies differs from subspecies setosa in having yellow-green hirsute upper parts of the plant and corollas 1.5-1.8(-2) cm long. Subspecies setosa has whitish gray hirsute upper parts and corollas 22.2(-2.5) cm long. Both subspecies are distributed in Xinjiang Province (China), Russia, and Kazakhstan, but subspecies transrhymnense extends into Mongolia as well. Onosma setosa was treated by Liu (1989) as 0. echioides L., but the latter is an entirely different species. Acknowledgments. I am indebted to Ihsan AlShehbaz and Tatiana Shulkina for help in the preparation of this manuscript.