Narrow Disc Research Articles

The Spectral Web of stationary plasma equilibria. II. Internal modes

The new method of the Spectral Web to calculate the spectrum of waves and instabilities of plasma equilibria with sizeable flows, developed in the preceding Paper I [Goedbloed, Phys. Plasmas 25, 032109 (2018)], is applied to a collection of classical magnetohydrodynamic instabilities operating in cylindrical plasmas with shear flow or rotation. After a review of the basic concepts of the complementary energy giving the solution path and the conjugate path, which together constitute the Spectral Web, the cylindrical model is presented and the spectral equations are derived. The first example concerns the internal kink instabilities of a cylindrical force-free magnetic field of constant α subjected to a parabolic shear flow profile. The old stability diagram and the associated growth rate calculations for static equilibria are replaced by a new intricate stability diagram and associated complex growth rates for the stationary model. The power of the Spectral Web method is demonstrated by showing that the two associated paths in the complex ω-plane nearly automatically guide to the new class of global Alfvén instabilities of the force-free configuration that would have been very hard to predict by other methods. The second example concerns the Rayleigh–Taylor instability of a rotating theta-pinch. The old literature is revisited and shown to suffer from inconsistencies that are remedied. The most global n = 1 instability and a cluster sequence of more local but much more unstable n=2,3,…∞ modes are located on separate solution paths in the hydrodynamic (HD) version of the instability, whereas they merge in the MHD version. The Spectral Web offers visual demonstration of the central position the HD flow continuum and of the MHD Alfvén and slow magneto-sonic continua in the respective spectra by connecting the discrete modes in the complex plane by physically meaningful curves towards the continua. The third example concerns the magneto-rotational instability (MRI) thought to be operating in accretion disks about black holes. The sequence n=1,2,… of unstable MRIs is located on one continuous solution path, but also on infinitely many separate loops (“pancakes”) of the conjugate path with just one MRI on each of them. For narrow accretion disks, those sequences are connected with the slow magneto-sonic continuum, which is far away though from the marginal stability transition. In this case, the Spectral Web method is the first to effectively incorporate the MRIs into the general MHD spectral theory of equilibria with background flows. Together, the three examples provide compelling evidence of the computational power of the Spectral Web Method.

A new species ofChoerophryne(Anura: Microhylidae) from Papua New Guinea

Abstract I describe a new species of small microhylid frog from the southern versant of New Guinea that is characterized by its long and narrow proboscis, relatively large size and long legs, narrow discs on all fingers, hidden tympanum, and details of color pattern. This represents the twelfth species of long-snouted Choerophryne known and the third from the southern versant of the island's Central Dividing Range. It is only known from a single specimen, so phylogenetic and biogeographic relationships remain unassessed.

A fossil genus of the Frullaniaceae (Porellales, Jungermanniopsida) from the mid-Cretaceous of Myanmar

Recent findings established the Albian-Cenomanian amber of Myanmar (Burmese amber) as an important source of Mesozoic cryptogams. Here, we describe an inclusion within Burmese amber as Protofrullania cornigera gen. et sp. nov. in the extant family Frullaniaceae (Porellales, Jungermanniopsida). Diagnostic characters include its incubous leaves consisting of a dorsal lobe and a ventral lobule forming a watersac, and strap-shaped, prominent underleaves producing a rhizoid bundle from the uppermost sector of the long, narrow disc. Bark fragments connected to some of the rhizoid bundles provide evidence that the fossil was an epiphyte.

A new legskate, Sinobatis andamanensis (Rajiformes: Anacanthobatidae),from the Andaman Sea (northeastern Indian Ocean).

A new legskate, Sinobatis andamanensis sp. nov. is described from a small collection of specimens taken off Phuket (Thailand) during an exploratory survey of the Andaman Sea. It is the first species of Sinobatis and the only legskate known from the northern Indian Ocean. Sinobatis andamanensis sp. nov. has an especially long and narrowly pointed snout (preorbital length exceeding 23% TL) with an interorbital distance 7-9.5 in snout length (up to 6.7 in other Sinobatis species). Molecular data are unavailable for most members of the genus, but based on morphology it shares with S. caerulea bluish dorsal and ventral surfaces when fresh and a long ventral head (length 36-42% TL). As well as differing in several morphometric differences, Sinobatis andamanensis sp. nov. seems to be a much smaller legskate (males adult from 186 mm DW vs. still immature at 540 mm DW in S. caerulea). Sinobatis bulbicauda also has an expanded posterior tail, but S. andamanensis sp. nov. differs from that species in having a narrower disc (width at anterior orbit 3.7-4.9 vs. 5.2-7.8 times mouth width) and anterior pelvic-fin lobes (base width 2.7-5.0 vs. 1.7-3.2 in distance between pelvic-fin origins), and shorter and less-conical tooth cusps and fewer vertebrae (total centra 126-133 vs. 148-171).

Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G 196-3 B

The origin of the very red optical and infrared colours of intermediate-age ($\sim$10 - 500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of dust may account for the observed reddish nature. We explored an alternative scenario by simulating protoplanetary and debris discs around G196-3B, which is an L3 young brown dwarf with a mass of $\sim 15$ $M_{\rm Jup}$ and an age in the interval 20 - 300 Myr. The best-fit solution to G196-3B's photometric spectral energy distribution from optical wavelengths through 24 $\mu$m corresponds to the combination of an unreddened L3 atmosphere ($T_{\rm eff} \approx 1870$~K) and a warm ($\approx$ 1280 K), narrow ($\approx$ 0.07 - 0.11 R$_{\odot}$) debris disc located at very close distances ($\approx$ 0.12 - 0.20 R$_{\odot}$) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass $\ge 7\times 10^{-10}$ M$_{\oplus}$ comprised of sub-micron/micron characteristic dusty particles with temperatures close to the sublimation threshold of silicates. Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G196-3B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height ($\approx 6 \times 10^3$ km). Our inferred debris disc model is able to reproduce G196-3B's spectral energy distribution to a satisfactory level of achievement.

Menopause as a potential cause for higher prevalence of low back pain in women than in age-matched men

SummaryFemale sex hormones play an important role in the aetiology and pathophysiology of a variety of musculoskeletal degenerative diseases. Postmenopausal women show accelerated disc degeneration due to relative oestrogen deficiency, resulting in narrower intervertebral disc space in women than age-matched men, increased prevalence of spondylolisthesis, and increased prevalence of facet joint osteoarthritis. Postmenopausal women also show higher osteoporosis related spine fracture rate, particularly at the thoracic–lumbar junction site. I propose the concept that low back pain (LBP) is more prevalent in postmenopausal women than age-matched men and is associated with the physiological changes caused by the relatively lower level of sex hormones after menopause in women. Considering hormone replacement treatment (HRT)'s consistent efficacy reported with menopause-associated osteoarthritis, an in-depth understanding of the role of the gonadal hormones in LBP modulation warrants further study. HRT initiated at early postmenopausal phase may be protective for recurring LBP. If this is the case, further cost–benefit analysis should be performed for optimal HRT regimen in cases of women with high risk of recurring severe LBP.

Lense–Thirring precession around supermassive black holes during tidal disruption events

A tidal disruption event (TDE) occurs when a star wanders close enough to a black hole to be disrupted by its tidal force. The debris of a tidally disrupted star are expected to form an accretion disc around the supermassive black hole. The light curves of these events sometimes show a quasi-periodic modulation of the flux that can be associated with the precession of the accretion disc due to the Lense-Thirring ("frame-dragging") effect. Since the initial star orbit is in general inclined with respect to the black hole spin, this misalignment combined with the Lense-Thirring effect leads to a warp in the disc. In this paper we provide a simple model of the system composed by a thick and narrow accretion disc surrounding a spinning supermassive black hole, with the aim to: (a) compute the expected precession period as a function of the system parameters, (b) discuss the conditions that have to be satisfied in order to have rigid precession, (c) investigate the alignment process, highlighting how different mechanisms play a role leading the disc and the black hole angular momenta into alignment.

Sometimes two arms are enough--an unusual life-stage in brittle stars (Echinodermata: Ophiuroidea).

Off West Africa (Angola-Morocco), benthos samples were collected in the years 2005-2012. These contained 124 specimens of brittle stars with two long arms and three extremely short or absent arms and an elongated, narrow disc. These unusual brittle stars, as well as 33 specimens with five fully developed arms, were identified as Amphiura ungulata. The specimens with unequal arms were juvenile stages, whereas adults had five equal arms. The large number of specimens with unequal arms suggests that this condition is not the result of damage and regeneration, but a normal growth pattern in this species. This study documents the morphology by SEM, amends the species description, and discusses possible explanations for the evolution of this condition. Although brittle star species with unequal arm growth have been reported, this is an extreme case that was unknown before this study.

INDIRECT DETECTION OF FORMING PROTOPLANETS VIA CHEMICAL ASYMMETRIES IN DISKS

We examine changes in the molecular abundances resulting from increased heating due to a self-luminous planetary companion embedded within a narrow circumstellar disk gap. Using 3D models that include stellar and planetary irradiation, we find that luminous young planets locally heat up the parent circumstellar disk by many tens of Kelvin, resulting in efficient thermal desorption of molecular species that are otherwise locally frozen out. Furthermore, the heating is deposited over large regions of the disk, ±5 AU radially and spanning azimuthally. From the 3D chemical models, we compute rotational line emission models and full Atacama Large Millimeter Array simulations, and find that the chemical signatures of the young planet are detectable as chemical asymmetries in observations. HCN and its isotopologues are particularly clear tracers of planetary heating for the models considered here, and emission from multiple transitions of the same species is detectable, which encodes temperature information in addition to possible velocity information from the spectra itself. We find submillimeter molecular emission will be a useful tool to study gas giant planet formation in situ, especially beyond AU.

Reduced Stark shift in three-dimensionally confined GaN/AlGaN asymmetric multi-quantum disks

The optical transitions of the three-dimensionally confined GaN/AlGaN asymmetric multi quantum disks were characterized by micro photoluminescence and time-resolved photoluminescence. Several fine emission lines, originating from the wide and narrow quantum disks, were observed around 3.7 eV from a single nanocolumn dispersed on a patterned SiO2 substrate. The photoluminescence from the wide quantum disk shifts a little with increasing excitation power, while that from the narrow quantum disk does not shift. This effect can be explained by carrier tunneling for the 3-dimensionally confined quantum disks. Kelvin probe force microscopy results confirm that the GaN/AlGaN multiquantum disks are surrounded by a GaN shell, which has a higher potential than core GaN.

The effects of screw configuration on the screw fill degree and special mechanical energy in twin-screw extruder for high-moisture texturised defatted soybean meal

To control the mechanical energy output by adjusting the screw configuration during soybean protein extrusion texturisation, the relationship between the screw configuration and the special mechanical energy was investigated. Different types of screw elements, element lengths and positions were designed and configured, while the other parameters were kept unchanged. The screw fill degree and specific mechanical energy output were detected. The results demonstrate that when the helix angle of conveying elements turns from forward (45°) to reverse (−37.5°), the disc width of the kneading elements decreases from 7.5mm to 5mm, and when the disc stagger angle turns from forward (45°) and forward (90°) to reverse (−45°), the screw fill degree and specific mechanical energy increase. When the length of the reverse kneading element increases, the screw fill degree and specific mechanical energy increase. When the distance between the reversing knead element and the die increases or the element space between the reversing knead element increases, the specific mechanical energy appears to decrease. Thus, the elements with reverse helix or stagger angles, narrow kneading disc, long length and flow-restricting ability increase the screw fill degree and induce high special mechanical energy. The special mechanical energy increases when the reverse kneading element is located at the screw position where the material viscosity is relatively high during extrusion.

The Impact of Initial Conditions in N-Body Simulations of Debris Discs

AbstractNumerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

Research of mechanical traction characteristics of direct sowing equipment

The objective of this study is to define the influ-ence of working speed on the traction force of a direct sowing machine with complex coulters and various press wheels (a narrow disc and a finger disc) under various soil compactions. The machine was pulled at three different speeds – 5 km•h-1, 7 km•h-1, and 9 km•h-1 – in soils of three different compactions. In the first trial soil compaction was 44 kPa at 50 mm depth, in the second trial – 493 kPa, in the third trial – 827 kPa. The traction force was measured using six sensors – three for horizontal force, two for vertical force, and one for side force. The research indicated that pulling direct sowing machine without a press wheel at working speed of 5 km•h-1 requires almost the same total traction force as pulling direct sowing machine with a narrow disc press wheel, while sowing machine with tined disc requires higher traction force at approximately 0.06 kN. Increasing the working speed of direct sowing machine with disc press wheel up to 7 km•h-1, horizontal traction force increases, while vertical traction force decreases. Increasing the working speed up to 9 km•h-1, the traction forces do not expose significant increase compared to the working speed of 7 km•h-1. DOI: http://dx.doi.org/10.5755/j01.mech.20.5.7149

Interspecific amphiploid‐derived alloplasmic male sterility with defective anthers, narrow disc florets and small ray flowers in sunflower

AbstractThe cytoplasmic male‐sterility (CMS)/fertility‐restoration system is important for hybrid sunflower (Helianthus annuus L.) seed production. The objective of this study was to characterize two novel alloplasmic CMSs, designated CMS GRO1 and CMS MAX3, with defective anthers, narrow disc florets with no swollen corolla, and short, narrow ray flowers derived from two tetraploid amphiploids (AMPs). Among 26 tested lines, only AMP Helianthus cusickii/P 21 and HA 410 failed to restore male‐fertility. Segregation of CMS, male‐fertile plants and plants with reduced male‐fertility was observed both in the testcross progeny of a six line half‐diallel cross of F1s with CMS MAX3 and in an F2 population of CMS GRO1 × RHA 274. Male‐fertility restoration was controlled by at least two dominant genes. Detailed analysis of the mitochondrial genes may provide insight into the differences between these CMSs and other CMS lines. The new CMSs will facilitate the studies of the incompatibility between cytoplasmic and nuclear genes, especially for the alloplasmic CMS involving perennial species, and also provide unique ornamental flower types and CMS sources for hybrid sunflower breeding.

Debris disc formation induced by planetary growth

Several hundred stars older than 10 million years have been observed to have infrared excesses. These observations are explained by dust grains formed by the collisional fragmentation of hidden planetesimals. Such dusty planetesimal discs are known as debris discs. In a dynamically cold planetesimal disc, collisional coagulation of planetesimals produces planetary embryos which then stir the surrounding leftover planetesimals. Thus, the collisional fragmentation of planetesimals that results from planet formation forms a debris disc. We aim to determine the properties of the underlying planetesimals in debris discs by numerically modelling the coagulation and fragmentation of planetesimal populations. The brightness and temporal evolution of debris discs depend on the radial distribution of planetesimal discs, the location of their inner and outer edges, their total mass, and the size of planetesimals in the disc. We find that a radially narrow planetesimal disc is most likely to result in a debris disc that can explain the trend of observed infrared excesses of debris discs around G-type stars, for which planet formation occurs only before 100 million years. Early debris disc formation is induced by planet formation, while the later evolution is explained by the collisional decay of leftover planetesimals around planets that have already formed. Planetesimal discs with underlying planetesimals of radii $\sim 100\,$km at $\approx 30$ AU most readily explain the Spitzer Space Telescope 24 and 70$ \mu$m fluxes from debris discs around G-type stars.

The bacterial contamination of allogeneic bone and emergence of multidrug-resistant bacteria in tissue bank.

Present study was carried out for the microbiological evaluation of allogeneic bone processed from femoral heads. A total 60 bacterial isolates comprising five different species including Streptococcus spp., Staphylococcus spp., Klebsiella spp., Bacillus spp., and Pseudomonas spp. were characterized based on their cultural and biochemical characteristics. Average bioburden was ranged from 5.7 × 101 to 3.9 × 104 cfu/gm. The majority (81.7%) of the microbial contaminants were detected as Gram positive with the predominant organism being skin commensal coagulase negative Staphylococci (43.3%). Antimicrobial resistance was evaluated by the activities of 14 broad and narrow spectrum antibiotic discs. Comparing the overall pattern, marked resistance was noted against Penicillin and Amoxicillin 100% (60/60). The most effective single antibiotics were Gentamicin, Tobramycin, and Ofloxacin which were bactericidal against 100% (60/60) isolates. Multidrug resistance (MDR) was confirmed in 70% (42/60) of the samples. Among them, the most prevalent antibiotypes were Penicillin, Amoxicillin, Oxacillin, Polymyxin, and Cefpodoxime (80% of total MDR). The study results revealed higher contamination rate on bone allografts and recommend the implementation of good tissue banking practices during tissue procurement, processing, and storage in order to minimize the chances of contamination.

Wave-like warp propagation in circumbinary discs – II. Application to KH 15D

KH 15D is a protostellar binary system that shows a peculiar light curve. In order to model it, a narrow circumbinary precessing disc has been invoked, but a proper dynamical model has never been developed. In this paper, we analytically address the issue of whether such a disc can rigidly precess around KH 15D, and we relate the precessional period to the main parameters of the system. Then, we simulate the disc's dynamics by using a 1D model developed in a companion paper, such that the warp propagates into the disc as a bending wave, which is expected to be the case for protostellar discs. The validity of such an approach has been confirmed by comparing its results with full 3D SPH simulations on extended discs. In the present case, we use this 1D code to model the propagation of the warp in a narrow disc. If the inner truncation radius of the disc is set by the binary tidal torques at {\sim} 1 AU, we find that the disc should extend out to 6-10 AU (depending on the models), and is therefore wider than previously suggested. Our simulations show that such a disc does reach an almost steady state, and then precesses as a rigid body. The disc displays a very small warp, with a tilt inclination that increases with radius in order to keep the disc in equilibrium against the binary torque. However, for such wider discs, the presence of viscosity leads to a secular decay of the tilt on a timescale of {\approx} 3000 ({\alpha}/0.05)^(-1) years, where {\alpha} is the disc viscosity parameter. The presence of a third body (such as a planet), orbiting at roughly 10 AU might simultaneously explain the outer truncation of the disc and the maintenance of the tilt for a prolonged time.

Sculpting the disk around T Chamaeleontis: an interferometric view

(Abridged) Circumstellar disks are believed to be the birthplace of planets and are expected to dissipate on a timescale of a few Myr. The processes responsible for the removal of the dust and gas will strongly modify the radial distribution of the dust and consequently the SED. In particular, a young planet will open a gap, resulting in an inner disk dominating the near-IR emission and an outer disk emitting mostly in the far-IR. We analyze a full set of data (including VLTI/Pionier, VLTI/Midi, and VLT/NaCo/Sam) to constrain the structure of the transition disk around TCha. We used the Mcfost radiative transfer code to simultaneously model the SED and the interferometric observations. We find that the dust responsible for the emission in excess in the near-IR must have a narrow temperature distribution with a maximum close to the silicate sublimation temperature. This translates into a narrow inner dusty disk (0.07-0.11 AU). We find that the outer disk starts at about 12 AU and is partially resolved by the Pionier, Sam, and Midi instruments. We show that the Sam closure phases, interpreted as the signature of a candidate companion, may actually trace the asymmetry generated by forward scattering by dust grains in the upper layers of the outer disk. These observations help constrain the inclination and position angle of the outer disk. The presence of matter inside the gap is difficult to assess with present-day observations. Our model suggests the outer disk contaminates the interferometric signature of any potential companion that could be responsible for the gap opening, and such a companion still has to be unambiguously detected. We stress the difficulty to observe point sources in bright massive disks, and the consequent need to account for disk asymmetries (e.g. anisotropic scattering) in model-dependent search for companions.

PAPSS2 mutations cause autosomal recessive brachyolmia

BackgroundBrachyolmia is a heterogeneous group of skeletal dysplasias that primarily affects the spine. Clinical and genetic heterogeneity have been reported; at least three types of brachyolmia are known. TRPV4 mutations...

Two syntopic new species of the Pristimantis orestes Group (Anura: Strabomantidae) from northwestern Peru

Two new species of Pristimantis (Anura: Strabomantidae), tentatively assigned to the P. orestes Group, are described fromhumid puna (3596 m) of Cañaris, Provincia de Ferreñafe, Región Lambayeque on the eastern slopes of the Cordillera Oc-cidental in northwestern Peru. Pristimantis mariaelenae sp. n. is a medium-sized species characterized by the dorsumvarying from brown to reddish ochre, groin and posterior surface of the thigh with white blotches, pearly white venter withbrown blotches, distinct tympanic annulus and membrane, and tubercles on the eyelid, heel, and outer edge of the tarsus.Pristimantis stipa sp. n. also is a medium-sized species characterized by having narrow discs without marginal grooves, distinct tympanic annulus and membrane present, and Toe III slightly longer than Toe V.