Higher Terminal Velocity Research Articles

Synthetic X-ray emission from white dwarf accreting planetary material

ABSTRACT The emission of hard X-rays associated with white dwarfs (WDs) can be generated by the presence of a stellar companion, either by the companion’s coronal emission or by an accretion disc formed by the material stripped from the companion. Recent studies have suggested that a Jupiter-like planet can also be a donor of the material whose accretion on to the WD can generate hard X-rays. We use the guacho code to reproduce the conditions of this WD–planet scenario. With the example of the hard X-ray WD KPD 0005+5106, we explore different terminal wind velocities and mass-loss rates of a donor planet for a future network of simulations to investigate the luminosity and the spectral and temporal properties of the hard X-ray emission in the WD–planet systems. Our simulations show that the material stripped from the planet forms a disc and accretes on to the WD to reach temperatures high enough to generate hard X-rays as usually seen in X-ray binaries with low-mass companions. For high terminal wind velocities, the planet material does not form a disc, but it rather accretes directly on to the WD surface. The simulations reproduce the X-ray luminosity of another X-ray accreting WD (G 29-38), and only sometimes reaches the hard X-ray luminosity of KPD 0005+5106. The X-ray variability is stochastic and does not reproduce the period of KPD 0005+5106, suggesting that the additional physical processes (e.g. hot spots resulting from magnetic channelling of the accreting material) need to be explored.

On the settling of aligned spherical particles in various quiescent media

We investigated experimentally the settling behaviour of vertically aligned spherical particles within various quiescent media at different release frequencies. The particles had a diameter of $d = 4$ mm and density of $\rho _s = 2200$ kg m $^{-3}$ , and were released near the free surface of water, ethanol, a G60 water–glycerine mixture (60 % glycerine by weight) and oil media at frequencies of $f_P = 4$ , 6 and 8 Hz, thereby allowing study of Galileo numbers, $Ga \in [16, 976]$ . Particle tracking velocimetry quantified the motion of nearly 800 particles in a 600 mm high tank, and particle image velocimetry examined flow patterns around the particles. Results revealed that the centre of mass of the particle trajectories exhibited preferential in-plane motions, with significant lateral dispersion and large $Ga$ in water and ethanol, and nearly vertical paths with low $Ga$ in the G60 mixture and oil media. Varying degrees of particle separation resulted in higher terminal velocities than for a single particle. Hence, particle drag decreased in all cases, with the oil medium showing the highest drag reduction under the closest particle separation, reaching up to nearly 70 % of that for the single particle. The vertical and lateral pair dispersions, $R^2_z$ and $R^2_L$ , exhibited ballistic scaling, with dependences on the initial separation, $r_0$ , and the type of medium. With large $Ga$ , $R^2_z$ displayed a ballistic regime followed by a slower rate, whereas with small $Ga$ , $R^2_z$ maintained a consistent ballistic regime throughout settling. Finally, normalized $R^2_z$ demonstrated distinct scaling (exponent 2/3 and 1) dependent on the normalized initial separation and $Ga$ .

Monitoring broad emission-line components in spectra of the two low-metallicity dwarf compact star-forming galaxies SBS 1420+540 and J1444+4840

ABSTRACT We report the discovery of broad components with P-Cygni profiles of the hydrogen and helium emission lines in the two low-redshift low-metallicity dwarf compact star-forming galaxies SBS 1420+540 and J1444+4840. We found small stellar masses of 106.24 and 106.59 M⊙, low oxygen abundances 12 + log O/H of 7.75 and 7.45, high velocity dispersions reaching σ ∼ 700 and ∼1200 km s−1, high terminal velocities of the stellar wind of ∼1000 and ∼1000–1700 km s−1, respectively, and large EW(H β) of ∼300 Å for both. For SBS 1420+540, we succeeded in capturing an eruption phase by monitoring the variations of the broad-to-narrow component flux ratio. We observe a sharp increase of that ratio by a factor of 4 in 2017 and a decrease by about an order of magnitude in 2023. The peak luminosity of ∼1040 erg s−1 of the broad component in L(H α) lasted for about 6 yr out of a three-decades monitoring. This leads us to conclude that there is probably a luminous blue variable candidate (LBVc) in this galaxy. As for J1444+4840, its very high L(H α) of about 1041 ergs s−1, close to values observed in active galactic nuclei (AGNs) and Type IIn supernovae (SNe), and the variability of no more than 20 per cent of the broad-to-narrow flux ratio of the hydrogen and helium emission lines over a 8 yr monitoring do not allow us to definitively conclude that it contains an LBVc. On the other hand, the possibility that the line variations are due to a long-lived stellar transient of type AGN/SN IIn cannot be ruled out.

Design and evaluation of INS/GNSS loose and tight coupling applied to launch vehicle integrated navigation

<abstract><p>A satellite launcher requires accurate and reliable navigation to reach orbit safely. This challenging application includes vertical launch, flying through diverse layers of the atmosphere, discontinuous acceleration and stages separation, high terminal velocities and hostile temperature and vibration ranges. The Inertial Navigation System (INS) is typically coupled with a Global Navigation Satellite System (GNSS) receiver to achieve the desired solution quality along the complete ascent trajectory. Here, several INS/GNSS integrated navigation strategies are described and evaluated through numerical simulations. In particular, we evaluate different INS/GNSS integration using: loose coupling, tight coupling and an intermediate Kalman filter on the receiver to enhance the loosely coupled navigation solution. The main contributions are: a compensation model of tropospheric delays on the GNSS observables, a compensation of processing/communication delays on GNSS receiver outputs, covariance adaptations to consider vehicle's high dynamics, and an specific way to integrate the filtered solution and its covariance provided by the GNSS receiver. The tightly coupled integrated navigation proved to be the best choice to handle possible GNSS receiver positioning solution outages, to exploit more degrees of freedom for the compensation of GNSS observables and the possibility to make a cross validation of individual GNSS observables with INS-based information. This is specially important during the periods with a low number of satellites in view when the GNSS positioning solution can not be validated or even computed by the GNSS receiver alone. Finally, a test with hardware in the loop is provided to validate the numerical result for the selected tightly coupled INS/GNSS.</p></abstract>

Terminal velocities of a deformed Leidenfrost liquid: Experiments and self-propulsion model

We derive a new model entirely from first principles to explain the Leidenfrost self-propulsion phenomenon in a quantitative way, where the deformable nature of the liquid has been taken into account for the first time. Our annular ring design enables liquid droplets to reach high terminal velocities, up to 0.42\ifmmode\pm\else\textpm\fi{}0.04 m/s, which is potentially beneficial to energy harvesting and flow chemistry applications.

Competition–colonisation trade‐offs are found among but not within wind‐dispersed Pinus species

Abstract The competition–colonisation trade‐off is recognised as a key mechanism for diversity maintenance, whereby weak competitors can avoid competition with stronger competitors due to their greater dispersal ability. To date, most theoretical and empirical work has focused on trade‐offs among different species yet a within‐species perspective is crucial to assess the scope for natural selection on competition–colonisation trade‐offs. For six wind‐dispersed Pinus species encompassing a wide range of seed masses, we examined whether within and among species there was evidence that heavier seeds typically disperse shorter distances but produce seedlings that are stronger competitors with a higher likelihood of successful establishment, under different treatment conditions. Within species, we found seedling establishment to be independent of diaspore terminal velocity (a measure of dispersal potential), which would maximise the variation in potential dispersal distances and locations reached by the seeds shed from a parent tree, and therefore the chances that some offspring will reach a favourable recruitment site. However, among Pinus species the likelihood of seedling emergence and survival was higher in species that produce heavier seeds with higher terminal velocity. We found a marked competition–colonisation trade‐off among all six species consistent with expectations from coexistence theory. In contrast, within species, there was no evidence of competition–colonisation trade‐offs for any species, despite differences in the relationships between diaspore mass and terminal velocity. This is consistent with weak selection within species for a competition–colonisation trade‐off. The results suggest that within‐species trade‐offs do not influence the risk of invasive spread. A free Plain Language Summary can be found within the Supporting Information of this article.

Hydrodynamics in a new liquid–solid circulating conventional fluidized bed

A new type of liquid–solid fluidized bed, named circulating conventional fluidized bed (CCFB) which operates below particle terminal velocity was proposed and experimentally studied. The hydrodynamic behavior was systematically studied in a liquid–solid CCFB of 0.032 m I.D. and 4.5 m in height with five different types of particles. Liquid–solid fluidization with external particle circulation was experimentally realized below the particle terminal velocity. The axial distribution of local solids holdup was obtained and found to be fairly uniform in a wide range of liquid velocities and solids circulation rates. The average solids holdup is found to be significantly increased compared with conventional fluidization at similar conditions. The effect of particle properties and operating conditions on bed behavior was investigated as well. Results show that particles with higher terminal velocity have higher average solids holdup.

Research on a New Process of Agile Turn with Engine Reignition Based on Optimal Control

A new process of agile turn with engine reignition is proposed in this paper. Compared with the traditional process, this process includes deceleration phase, larger angle manoeuvre phase, and engine reignition phase. Firstly, the paper describes the new process of agile turn. Then, several constraints in this process are described. Considering all these constraints and assumptions, a new dynamic model including two-stage engine and deceleration parachute is established. Then, the optimal control laws are designed and the timing point determination of the secondary engine ignition is discussed. By using Pontryagin principle, the optimal control laws for each actuator are derived. In terms of determining the optimal timing point of the secondary engine ignition, the paper gives the process of proof. Finally, several numerical simulations are given to demonstrate the effectiveness of the method proposed in this paper. According to all these numerical simulations, it is obvious that the new process of agile turn proposed in this paper is better than traditional process especially in having a smaller turning radius, a shorter turning time, and a high terminal velocity.

Plant reproductive traits in old and recently-restored temperate forest understories

Recently-restored forests on former agricultural land have impoverished herbaceous understories. This is partly due to the poor colonizing capacity of understory plants, which makes them slow in responding to land use change. Functional traits can be used to compare old and recent understories and provide insight about which plant syndromes are missing after restoration intervention. In this work, we focus on the seed and germination traits of herbaceous understories, investigating how they influence community assembly in restored woodlands.We studied temperate deciduous oak forests in two locations at the centre and southern limit of the European Atlantic region (Loder Valley Nature Reserve, England; and Tragamón Oak Grove, Spain). In each location, we sampled a pair of old and recently-restored forest sites and established 10 permanent plots, where we surveyed understory species abundances every two months for one year. We recorded plant reproductive traits for the species found and measured germination traits in laboratory experiments with seeds collected in situ. Finally, we calculated community-weighted means (CWM) for each trait and plot.The reproductive traits of old and recent forest understory species had significant differences in both locations. Old forest communities had shorter plants that flowered earlier and were more dependent on vegetative reproduction. They produced less seeds, which were heavier and had higher terminal velocity. The germination of these seeds occurred at colder temperatures and was less dependent on light. However, some dormancy-related traits seem more related to bioclimatic differences between the two locations (England and Spain).Old and recently-restored communities vary consistently for several reproductive traits, with old community traits reflecting a poor dispersal capacity and a specialized germination niche in shaded habitats under a deciduous canopy. When designing species mixes for restoration efforts, plants with particular old understory traits should be given priority.

Potential risk of interspecific hybridization in ex situ collections

Spontaneous hybridization in ex situ conservation facilities could potentially contaminate endangered plant species destined for the reintroduction into the wild. Despite the general recognition of the importance of such danger, studies exploring the consequences of hybridization including subsequent performance of the hybrids in comparison to the original species are rare. The aim of the present study was to assess the potential consequences of hybridization between the endangered endemic serpentinophyte species, Minuartia smejkalii, and its congener allopatric species, M. caespitosa. We performed controlled inter-specific crosses and compared seed production, germination, growth, seed morphology and dispersal ability between M. smejkalii and the hybrids. Our results showed that M. smejkalii and M. caespitosa can hybridize and produce viable seeds. Number of seeds per capsule produced by M. smejkalii and the hybrids did not differ but germination rates were higher in the hybrids. In addition, hybrids produced a higher number of flowers than M. smejkalii in open sites and serpentine soils, indicating that the hybrids perform better in the extreme serpentine conditions than the original serpentine species. Our simulation results showed a higher dispersal potential in hybrids compared to M. smejkalii despite their higher terminal velocity. Our results provide evidence that hybrid individuals from ex situ collections might outcompete the endemic M. smejkalii in the wild, if they are introduced by mistake. Therefore, for conservation and reintroduction purposes, ex situ hybridization events should be considered as a potential threat and treated carefully. We recommend establishing an adequate management of potentially crossable species and cautiously selecting individuals to be used for restoration.

Limited evidence for a consistent seed mass‐dispersal trade‐off in wind‐dispersed pines

Abstract Much of the variation in dispersal potential among seeds of different plant species has been related to a putative trade‐off between dispersal potential and seed mass. Yet to date there are few taxonomically controlled comparisons that explore the generality of this relationship across and within multiple species. We measured the seed mass and dispersal traits across multiple pine species that encompassed a 100‐fold range in seed mass. We expected that for the larger seeded species, the resource investment required in the cone to house seeds and their wings may constrain dispersal potential. We examined the relative roles of samara and cone traits in determining the terminal velocity, and investigated how the relative investment of resources in cone structure related to seed mass and samara dispersal traits. Finally, we examined the partitioning of variation in seed mass and terminal velocity within and among individuals of each species. We found a strong positive relationship between seed mass and samara terminal velocity across all 12 species; however, this seed mass‐dispersal trade‐off was only significant within two of our species. For most species, wing loading was the most important trait determining samara terminal velocity. Across species, increases in cone investment were associated with heavier seeds with longer wings but higher terminal velocities, while within‐species increases in cone investment were associated with decreases in terminal velocity. The majority of the variation in terminal velocity occurred within individual trees, while seed mass variation mostly occurred among trees and may therefore be subject to stronger selection pressure. Synthesis. We have found strong support for a trade‐off between seed mass and dispersal potential across a wide range of wind‐dispersed Pinus species. Importantly, we show that this trade‐off is largely absent within species, potentially reducing selective pressure. This may be largely due to the relationships between cone investment and samara traits, whereby increases in cone investment result in a proportionally greater increase in wing size than seed mass. Where resources are limited, investment in seed mass may be prioritized over dispersal.

Nonintrusive investigation of large Al-kaolin fractal aggregates with slow settling velocities

Although a combination of aggregate characteristics dictate particle settling, it is commonly assumed that large particles have higher terminal velocities. This simplifying assumption often leads to overprediction of large aggregate settling velocities which in turn negatively impacts on estimates of sedimentation clarification efficiency. Despite its importance, little attention has been given to large aggregates with slow-settling velocities. This paper addresses this gap by investigating slow-settling velocities of large, heterodisperse and multi-shape Al-kaolin aggregates using non-intrusive methods. A particle image velocimetry technique (PIV) was applied to track aggregate velocity and a non-intrusive image technique was used to determine aggregate characteristics, including size (df), three-dimensional fractal dimension (Df), density (ρf), aggregate velocity (Vexp) and Reynolds number (Re). Results showed no strict dependence of settling velocity on large aggregate size, shape and density, as Al-kaolin aggregates with the same size exhibited different settling velocities. A comparison of the results with the well-known Stokes’ law for velocity modified by a shape factor showed that the settling velocities measured here can vary from 2 to 14 fold lower than the predicted values for perfect sphere-shape aggregates with the same density and size. Furthermore, results have also shown large Al-kaolin aggregate's drag coefficient (Cd) to be around 56/Re, for average fractal aggregate sphericity of around 0.58.

Systematic Study of Pressure Fluctuation in the Riser of a Dual Inter-Connected Circulating Fluidized Bed: Using Single and Binary Particle Species

This study systematically investigates the pressure fluctuation in the riser of a dual interconnected circulating fluidized bed (CFB) representing a 10 kWth cold-flow model (CFM) of a chemical-looping combustion (CLC) system. Specifically, a single-species system (SSS) and a binary-mixtures system (BMS) of particles with different sizes and densities were utilized. The pressure fluctuation was analyzed using the fast Fourier transform (FFT) method. The effect of introducing a second particle, changing the inventory, composition (i.e., 5, 10 to 20 wt.%), particle size ratio, and fluidization velocity were investigated. For typical SSS experiments, the results were similar to those scarcely reported in the literature, where the pressure fluctuation intensity was influenced by varying the initial operating conditions. The pressure fluctuations of BMS were investigated in detail and compared with those obtained from SSS experiments. BMS exhibited different behaviour; it had intense pressure fluctuation in the air reactor and in the riser when compared to SSS experiments. The standard deviation (SD) of the pressure fluctuation was found to be influenced by the fluidization regime and initial operating conditions, while the power spectrum density (PSD) values were more sensitive to the presence of the particles with the higher terminal velocity in the binary mixture.

Tracing the signs of local dispersal in the temperate forest understorey using spatially structured vegetation data

AbstractQuestionsDispersal is important for the formation of biodiversity patterns. However, studying dispersal is difficult, particularly in established communities. We examined local dispersal processes in the forest herbaceous layer by looking at the abundance of plants in the neighbourhood of the surveyed plots and using dispersal traits and fecundity‐related attributes.LocationThermophilous oakwood in south Moravia, Czech Republic.MethodsWe collected plant community and environmental data from 2 m × 2 m plots nested in a 5 m × 5 m square grid, covering 0.36 hectares of temperate forest. We created binomial generalised linear models of species occurrence in the 2 m × 2 m plots, using species frequencies in four adjacent 5 m × 5 m plots (plot neighbourhood) and environmental data, to account for dependence caused by habitat factors. We analysed the relationships between neighbourhood effects and species attributes using linear regression.ResultsApproximately one third of species had a stronger association to neighbourhood alone than to local environment factors. For the remaining species, there was a large joint effect of neighbourhood and environment. However, the link between dispersal traits and the neighbourhood effect was weak. The trait analyses showed that plumed appendages were negatively correlated to neighbourhood effects, whereas possession of elongated appendages, high terminal velocity, clonal spread and absence of seed appendages exhibited insignificant positive relationships to the neighbourhood.ConclusionsAt the scale of metres, the distributional patterns of forest herbs cannot be solely associated with dispersal. The reasons could be methodological: our data contain a limited set of species with mostly database‐derived attributes. However, there may also be ecological mechanisms involved. The spatial distribution of plants could be modified by limited seed production and further reshaped by extinctions during earlier ontogenetic stages.

Use of Software for Image Analysis and Calibration of Automated Rain Simulator

Aims: To calibrate and evaluate a rain simulator, with automatic operation, as well as determine the average size, the effect of the height of the equipment (2.12; 2.42 and 2.72 m) and of the oscillations of the spray nozzle of the rain simulator (21, 29 and 40 oscillations min-1). Finally, to test and to compare the results of the count of drops by the software of analysis and processing of images Able Image Analyser, ImageJ and Safira.
 Study Design: The experimental design was completely randomized, with 3 x 3 x 3 factorial scheme, with three repetitions (81 units).
 Place and Duration of Study: The research was conducted in a greenhouse, in the municipality of Rondonópolis, Mato Grosso, located geographically at latitude 16°27'49 "S, longitude 550°34'47" W.
 Methodology: For the calibration tests, the rainfall simulator was adjusted according to the heights (2.12; 2.42 and 2.72 m) and oscillations (21, 29 and 40 oscillations min-1), followed by trays with a uniform layer of wheat flour, 2 cm thick, where the simulated raindrops were sprayed for a period of 4 seconds. From this procedure, the drops were dried, sifted, weighed and counted. Droplet analysis was performed using three image analysis software Able Image Analyser, ImageJ and Safira.
 Results: The softwares Able Image Analyzer, ImageJ and Safira did not show any significant difference in counting of the number of drops. It was observed that in the oscillation factor in setting that if gets drops of larger size (21 oscillations min-1) the terminal velocity is also greater. In the height factor of the equipment, the drops presented larger sizes at the lower height (2.12 m). There are larger drops, higher terminal velocity as the height of the spray nozzle decreases, and higher kinetic energy value per unit area as the height of the spray nozzle increases. The range of drop sizes observed was 1.2 mm to 3.1 mm.
 Conclusion: Although the software does not present significant differences, the ImageJ software proved to be more suitable as a research tool, since it has the license of free use and greater ease of use. Satisfactory results were obtained compared to natural rains in more than one combination of height and swings.

CFD analysis on the directional stability and terminal velocity of the OMNI-Max anchor with a booster

The OMNI-Max anchor, a newly developed gravity installed anchor, offers a cost effective anchoring solution with improved reliability for deep-water mooring facilities. However, the anchor final penetration depth is relatively shallow in the soil with high strength gradient. A booster, which can be attached at the tail of the OMNI-Max anchor, is designed with the aim to improve both the anchor directional stability and terminal velocity, such that the anchor can penetrate deeper into the seabed and consequently gain higher holding capacity. The objective of this paper is to investigate the directional stability and terminal velocity of the OMNI-Max anchor and hybrid anchor (i.e. an OMNI-Max anchor with a booster) based on the computational fluid dynamics (CFD) approach. The numerical simulation results demonstrated that the booster is beneficial in moving the position of the hydrodynamic centre towards the anchor rear, hence the directional stability of the hybrid anchor is improved. Moreover, the anchor terminal velocity was increased from 22.44 m/s to 32.01 m/s by the aid of a booster. Finally, an optimised design on the booster geometry was performed to ensure that the hybrid anchor can obtain high terminal velocity and maintain directional stability at the same time.

PREPARATION OF MICRON-SIZED DROPLETS AND THEIR HYDRODYNAMIC BEHAVIOR IN QUIESCENT WATER

To study the hydrodynamics of rising droplets (especially less than 1 mm) in quiescent water, a microfluidic device with co-flowing configuration was integrated to prepare micron-sized droplets. Soybean oil and toluene droplets of size from 100 to 600 µm were obtained by five co-flowing devices with different capillary sizes. It is found that the capillary device with smaller tip size produces smaller droplets and, for a given device, the droplet size decreases with the increase of continuous phase flow rate. Alternatively, the increase of dispersed phase flow rate has little influence on the droplet size. To predict the droplet size, a correlation for dimensionless droplet diameter as a function of Capillary number (Ca), Reynolds number (Re) and viscosity ratio was proposed. Then, the hydrodynamics of a single droplet and of droplet swarms rising in quiescent water were extensively investigated. The experimental results show that the terminal velocity of a single micro-droplet is consistent with that of rigid spheres with the same size and density, while the terminal velocity of a droplet swarm is obviously higher than that of a single droplet. Experimental observation shows that the motion of a droplet swarm in static water is such a manner that each droplet alternately accelerates by chasing others, causing a higher terminal velocity. Furthermore, the terminal velocities of millimeter-sized toluene droplets rising in water were measured. Compared with rigid spheres, the droplets of dp=1~4.6 mm have higher terminal velocities, while the droplets of dp>4.6 mm have lower terminal velocities. Finally, by taking into account the interfacial tension, internal circulation and shape deformation, a comprehensive explanation is proposed to describe the variation of the drag coefficient with the droplet size ranging from microns to millimeters.

Creeping flow of a wormlike micelle solution past a falling sphere: Role of boundary conditions

Creeping flow of a wormlike micelle solution past a falling sphere with varying surface roughness is considered. A combination of particle tracking velocimetry, particle image velocimetry and microscopy is used to obtain detailed information on the flow of the wormlike micelle solution based on CTAB/NaSal (9 mM/9 mM) around the falling spheres. We find that the surface roughness strongly affects the dynamics of the sphere motion in wormlike micelles such that roughened spheres fall with higher terminal velocities than smooth spheres. In addition, for the roughened spheres the stagnation point is closer to the sphere center of mass, and the magnitude of the negative wake is stronger. We also report, for the first time, formation of micron-size air bubbles at the surface of roughened spheres that are responsible for these unusual results. When these microbubbles are removed, roughened spheres fall with similar velocities as smooth spheres. The latter result may be considered as indirect evidence for no-slip boundary conditions in this CTAB/NaSal system. This hypothesis is further validated with local velocity profile measurements for the wormlike micelle solution sheared in a custom built Taylor–Couette geometry.

Seed traits, terminal velocity and germination in sexual diploid and apomictic triploid Hieracium alpinum (Asteraceae): Are apomicts better dispersers?

In this study, we examined the effect of seed characteristics (seed weight, seed length, seed width, pappus length and pappus width) and ploidy level on seed terminal velocity and germination in Hieracium alpinum, an arcto-alpine anemochorous species with vicariant diploid sexual and triploid apomictic populations producing diploid and triploid seeds, respectively. Importantly, triploids occupy a considerably larger range than diploids, suggesting that they have better colonization abilities putatively mediated by increased dispersal potential of the former. In total, 970 seeds collected from 228 mother plants from 30 populations across the distribution range were analysed. Diploid and triploid seeds did not differ significantly in most morphological traits, except for triploid seeds being wider. Terminal velocity was greater in diploid seeds compared to triploid seeds. This difference was not significant if a nested design (ploidy, population, mother plant) was used but significant if the population level was not considered, indicating high interpopulation variation in this trait. Terminal velocity was positively and significantly correlated with seed mass, length and width and negatively correlated with pappus length and width. Germination probability was positively associated with seed mass and negatively with ploidy (higher in diploids, compared to triploids). Our results thus indicate partly opposite dispersal-establishment strategies of diploid sexual and triploid apomictic biotypes of H. alpinum. One the one hand, the slightly greater values of terminal velocity of diploid seeds might reduce their dispersal potential, but on the other, their significantly greater germination rates, when compared to triploid seeds are likely to allow their more successful establisment. To sum up, our result do not support the hypothesis of heavier seeds with higher terminal velocity and higher germination rates in autopolyploids compared to their diploid progenitors.

Correlations between the germination capacity and selected physical properties of cultivated radish seeds

Relationships between the physical properties of seed and their germination capacity and energy is an important consideration for separating seeds of the highest or lowest quality. The objective of this study was to determine the correlations between the selected aerodynamic, geometric, frictional and mass parameters of cultivated radish (Raphanus sativus L.) seeds and their germination capacity for the purpose of improving seed quality. The parameters were determined for graded and discarded radish seeds and impurities were separated by a gravity separator. A germination test was performed, its results were verified every 12 hours, and the germination rate index was determined. A statistical analysis revealed that germinated and non-germinated seeds from the graded fraction did not differ significantly. In the discarded fraction, germinated seeds were characterized by higher terminal velocity (by approx. 10%), thickness (by approx. 9%) and mass (by approx. 26%) in comparison with non-germinated seeds. Significant positive correlations were noted between the germination time vs terminal velocity and mass of discarded seeds. Thus, the separation of radish seeds should take place in two stages using a gravity separator and a pneumatic separator. A vertical stream of air with the speed of approx. 8 m s -1 allows recovery of around 37% of discarded seeds that contain approx. 86% of healthy germs. The resulting seed mixture is characterized by greater germination energy and capacity than the seed fraction graded on a gravity separator only.