Outer Ridge Research Articles

Influence of Ocean Circulation and Benthic Exchange on Deep Northwest Atlantic Nd Isotope Records During the Past 30,000 Years

AbstractNeodymium (Nd) isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance. To better constrain the controls of water mass provenance and nonconservative effects on the archived Nd isotope signal, we present a new depth transect of Nd isotope reconstructions from the Blake Bahama Outer Ridge along the North American continental margin covering the past 30 ka. We investigated five sediment cores that lie directly within the main flow path of the Deep Western Boundary Current, a major advection route of North Atlantic Deep Water. We found offsets between core tops and seawater Nd isotopic compositions that are observed elsewhere in the Northwest Atlantic. A possible explanation for this is the earlier suggested redistribution of sediment by nepheloid layers at intermediate as well as abyssal depths, transporting material downslope and along the continental margin. These processes potentially contributed to Nd isotope excursions recorded in Northwest Atlantic sediment cores during the Bølling‐Allerød and early Holocene. An Atlantic‐wide comparison of Nd isotope records shows that the early Holocene excursions had an additional contribution from conservative advection of unradiogenic dissolved Nd. Nevertheless, the trends of the Nd isotope records are in general agreement with previous reconstructions of water mass provenance from the entire Atlantic and also reveal millennial‐scale changes during the last deglaciation in temporal high resolution, which have rarely been reported before. Further, the new records confirm that during cold periods the Northwest Atlantic was bathed by an increased contribution of southern sourced water.

Late Quaternary climate and environmental change derived from glacial deposits in the Parlung Zangbo Valley, southeastern Tibetan Plateau

ABSTRACTThis study investigated the late Quaternary climate and environmental characteristics of two tributary valleys (Xingmu and Depu Valleys) in the Parlung Zangbo Valley, southeastern Tibetan Plateau. Optically stimulated luminescence (OSL) samples collected from moraines at the mouth of Xingmu Valley produce a wide age range from 13.9 ka to 76 ka. The ages measured from the lenticular sand are consistent with the relative geomorphic sequence of the landforms. Lenticular sand layers below the moraine were dated to 37.9 ka and 44.7 ka, indicating that fluvial processes were likely dominant in the valley during Marine Isotope Stage (MIS) 3. The outer moraine ridges at the valley mouth were formed during 13.9 ka and 26.5 ka, corresponding to MIS2. At Depu Valley, OSL samples from two sets of lateral and terminal moraines close to the modern glacier, provide ages from 1.4 ka to 29.2 ka. The paleosol layer widely developed during 2.6 cal ka BP and 8.7 cal ka BP in the study area, reflecting a relatively warm condition during the mid-Holocene.

Bosumtwi impact structure, Ghana: Evidence for fluidized emplacement of the ejecta

AbstractThe about 10.5 km diameter Bosumtwi impact crater is one of the youngest large impact structures on Earth. The crater rim is readily noticed on topographic maps or in satellite imagery. It defines a circular basin filled by water (Lake Bosumtwi) and lacustrine sediments. The morphology of this impact structure is also characterized by a circular plateau extending beyond the rim and up to 9–10 km from the center of the crater (about 2 crater radii). This feature comprises a shallow ring depression, also described as an annular moat, and a subdued circular ridge at its outer edge. The origin of this outermost feature could so far not be elucidated based on remote sensing data only. Our approach combines detailed topographic analysis, including roughness mapping, with airborne radiometric surveys (mapping near‐surface K, Th, U concentrations) and field observations. This provides evidence that the moat and outer ring are features inherited from the impact event and represent the partially eroded ejecta layer of the Bosumtwi impact structure. The characteristics of the outer ridge indicate that ejecta emplacement was not purely ballistic but requires ejecta fluidization and surface flow. The setting of Bosumtwi ejecta can therefore be considered as a terrestrial analog for rampart craters, which are common on Mars and Venus, and also found on icy bodies of the outer solar system (e.g., Ganymede, Europa, Dione, Tethys, and Charon). Future studies at Bosumtwi may therefore help to elucidate the mechanism of formation of rampart craters.

Effect of different miniplate osteosynthesis in different mandibular angle fracture patterns on bite force: A 3D finite element analysis

ObjectiveBite force can be used as a clinical indicator of masticatory performance. As bite force is reduced with fractures and also, miniplate fixation has become the standard treatment, the aim of this study is to determine the optimal method for mini-plating in the fracture of the mandible angle to reach the best mastication power. MethodsA three-dimensional model generated from CBCT (Cone-beam computed tomography) of human mandible for Finite Element Analysis. Four different fracture patterns were simulated on the models. Each fracture pattern was fixed by five different methods of miniplate fixation. Each compared to others after simulation and applying the force of the masticatory muscles and result reported in Newton unit. ResultsThe highest mastication force belonged to a pattern in which a miniplate was placed on an outer oblique ridge and another miniplate in the lower border of the buccal mandibular cortex. The lowest mastication force also belonged to placing a mini plate on the upper side of the cortex. ConclusionFinite Element Analysis is an effective method for indirect measurement of mastication power. In order to biomechanically rebuild optimal mastication force in patients with fracture of the lower angle of the jaw, it is recommended to use two miniplates in two different planes.

Spatial and temporal cross-cutting relationships between fault structures and slope failures along the outer Kumano Basin and Nankai accretionary wedge, SW Japan

Abstract New, high-resolution multi-beam bathymetric data from RV Sonne cruise SO251 show a widely variable surface morphology along the southern Kumano Basin and Nankai accretionary prism off SW Japan. Combined with a three-dimensional seismic volume, these data provide insight into the ubiquitous and varied nature of faulting typical of accretionary prism settings, a high number of submarine landslides across the entire study area that vary both spatially and temporally, a pronounced absence of slide deposit bathymetric manifestations, widely varied slope angles and a potential subducted seamount scar. We have mapped scars of 442 primary and 184 secondary landslides and have measured the areas evacuated by these slides. Most of the slides are completely disintegrative, so surficial landslide deposits are almost absent. The incidence with which temporally sequential slope failures and fault structures cross-cut themselves and one another provides evidence of potential failure pre-conditioning such as gas hydrates, pore fluid overpressures and bottom current activity. Seismic loading and slope over-steepening are then the most likely final trigger mechanisms to slope failure. The majority of observed landslides (64%) occur seawards of the outer ridge, providing insight into the relationship between surficial landsliding and subsurface tectonic processes along this accretionary prism.

Characterization of hydrate and gas reservoirs in plate convergent margin by applying rock physics to high-resolution seismic velocity model

Gas hydrates are widely distributed in the Kumano forearc basin, which is located above accretionary prism in the Nankai margin off the Kii peninsula, Japan. Bottom-Simulating Reflector (BSR) at the base of gas hydrate stability zone has been imaged as a strong acoustic impedance contrast on the reflection seismic profiles. In order to better define the accumulations of gas hydrates and free gases, we performed a high-resolution seismic velocity analysis to 3D seismic data using a method of conventional semblance spectra via automatic velocity picking algorithm. The results revealed that gas hydrate-bearing sediments above the BSR and free gas-bearing sediments below the BSR are characterized by P-wave velocities of 1900–2500 m/s and 1000–1800 m/s, respectively. Then, the velocity model was converted into gas hydrate and free gas saturation using rock physics approaches. The results indicated that saturation of gas hydrates ranges from 0% to 45% in the pore space, and highly concentrated around the outer ridge where faults are densely developed. Additionally, concentrations of free gas ranging from 0% to 20% in the pore space are widely distributed below BSRs and are considerably high above ridge structure generated by displacement of large fault splayed from the deep plate boundary décollement. Based on these results, we suggest that the gas hydrates concentrated due to the free gas influx which migrated upward through the steeply dipping strata and faults (or fractures) cutting through the basin. The accumulations of gas and/or hydrates are further controlled by fault movements in the accretionary prism beneath the forearc basin. Therefore, these factors generated by intensive tectonic movements in the plate subduction zone control the distribution and saturation pattern of gas hydrate and free gas formations.

An innovative PVC mandrel for controlling the cross-sectional deformation of double-ridged rectangular tube in rotary draw bending

In order to control the cross-sectional deformation of double-ridged rectangular tube (DRRT) in rotary draw bending (RDB), a PVC mandrel just supporting the back of ridge grooves was introduced. The characteristics of cross-sectional deformation of DRRT and its evolution with the new PVC mandrel were revealed numerically by comparing with that with the mandrel-core die. In order to evaluate the application scope of the new PVC mandrel, the cross-sectional deformation for different specifications of DRRT in RDB were also researched. The results show that: (1) the flange sagging Δh, space deformation between ridges Δd, and width deformation of inner ridge groove Δw by using the new PVC mandrel can be better controlled than that by using the mandrel-core die. But the width deformation of the outer ridge groove ΔW gets a little larger; (2) by using the new PVC mandrel, the maxima of absolute values of Δh and Δw and the maximum of ΔW all increase firstly with the process of bending and then change little when the bending angle is larger than 60°, which are consistent with the variation of the peak value of tangent stress on the flange, while the maximum of absolute value of Δd increases continuously. (3) For small-sized DRRT, its cross-sectional deformation can be well controlled by using the new PVC mandrel. However, with the increase of dimension of DRRT, the cross-sectional deformation of DRRT increases obviously, and its distribution is extremely non-homogeneous.

Four-step Tensioning Construction Method and Experimental Study for Rigid Bracing Dome

Rigid bracing dome is a new pre-stressed space structure. In the study, according to the features of the new space structure, a four-step tensioning construction method is proposed and corresponding tensioning control principle is also given. The rigid bracing dome designed in the experimental study has a diameter of 6 m and is equally divided into eight parts in the circumferential direction. The four-step tensioning construction method is explored in detail. The synchronous symmetric tensioning schemes in eight directions, four directions and two directions are studied respectively. The deviations of the experimental model are analyzed by using the orthogonal test design method. The key experimental problems are analyzed to propose corresponding solutions. The construction method is simple and efficient. An appropriate symmetric tensioning scheme can be chosen according to the requirements of practical projects. The deviation of outer ridge cable force is mainly caused by the following factors: vertical coordinates of support and rods, and the lengths of outer ridge cable, inner ridge cable, inner ring rod, and outer ring rod. The coordinate deviations of center rods are mainly affected by the lengths of outer ring rod and inner ridge cable. The construction method and corresponding solutions can be used to guide engineering practices.

Submarine glacial landforms and sedimentary environments in Vaigattbogen, northeastern Spitsbergen

Vaigattbogen is located in northern Svalbard. The area is currently affected by several tidewater glaciers. This study uses multibeam-, sub-bottom acoustic data, and four sediment cores to reconstruct the Late Weichselian and Holocene glacial history in Vaigattbogen. During the last glacial, ice flowed northwards through Vaigattbogen and fed into the Hinlopen Strait Ice Stream. Streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities. De Geer moraines in the shallower parts of Vaigattbogen imply that multiple halts and/or re-advances interrupted the ice retreat in these areas. A sediment core suggests that the north basin deglaciated prior to 9.1cal.kaBP. In the south basin, two large moraine ridges and networks of crevasse-squeeze ridges suggest that at least two surge-type advances occurred during the Holocene. The Hinlopenbreen glacier surged in the early 1970s and deposited the inner (R.2) of the two large moraine ridges. Radiocarbon ages from a sediment core recovered from the crest of the outer (R.1) ridge yield a basal age of 2.6cal.kaBP. However, the core did not sample subglacial diamict and the age of the ridge could be anything between 2.6cal.kaBP and early Holocene. The R.1 ridge formed prior to the Little Ice Age (LIA), implying that more than one tidewater glacier has experienced a pre-LIA surge on the east coast of Spitsbergen, suggesting that surging during the Holocene was a regional phenomenon. The R.1 ridge is double-crested with small crevasse-squeeze ridges between the crests suggesting that more than one surge-type advance occurred during the Holocene reaching approximately the same location. Data from eastern Svalbard indicate differences in surge-landform assemblages suggesting that different mechanisms could have governed surge-cycles throughout the Holocene.

Petrochemical and Petrotectonic Characterisation of Ophiolitic Volcanics from Great Nicobar Island Andaman-Sumatra Belt

ABSTRACT In Great Nicobar island ophiolite is restricted to the eastern coast of the island and occur as small isolated out crops in the terrain of Oligocene sediments. The ophiolitic rocks are represented by pillowed basalt, massive andesite and pyroclastic andesite. These volcanics represent dismembered members of the upper part of the ophiolite. Basalt is porphyritic in nature where phenocrysts of augite and plagioclase laths are set in a fine grained glassy to chloritic matrix. Andesites consists of phenocrysts of augite, altered feldspar and minor quartz which are set in ground mass of epidote-chlorite glass. Trace element and REE pattern suggests more fertile mantle source for andesite than that of basalt. Trace element characteristics indicate that the andesites and basalts were possibly derived from the same melt where andesite represents the more fractionated product. In Andaman Islands dismembered ophiolite with complete ophiolite stratigraphy are found only within the Eocene sediments. But the field disposition suggests that in Great Nicobar emplacement of the ophiolite continued even after the Oligocene sedimentation. The characters of the ophiolitic rocks in Great Nicobar island are similar to that of the Sunda outer arc ridge.

Multi-Objective Parameter Optimization for Cross-Sectional Deformation of Double-Ridged Rectangular Tube in Rotary Draw Bending by Using Response Surface Methodology and NSGA-II

Cross-sectional deformation of double-ridged rectangular tube (DRRT) inevitably occurs due to the inhomogeneous deformation induced by external boundary conditions in rotary draw bending (RDB). Unreasonable factor combination would aggravate the cross-sectional deformation of DRRT. So, a powerful and efficient method combining Response Surface Methodology (RSM) and Non-Sorted Genetic Algorithm II (NSGA-II) was proposed to optimize the factors to control the cross-sectional deformation of DRRT in RDB. Firstly, an orthogonal experiment was used to screen out the important factors. It was obtained that three factors—clearance between DRRT and mandrel, clearance between DRRT and bending die, and boosting of pressure die—have an important influence on the cross-sectional deformation of DRRT. It can also be observed that the variation trend of flange sagging (FS) is always consistent with that of space deformation between ridges (SDR) with the changing of factors. RSM based on a Box-Behnken design was then used to establish response surface models. The proposed response surface models were used to analyze the relationship of the important parameters to the responses, such as space deformation between ridges, and width deformation of outer and inner ridge grooves (WDO and WDI). Finally, multi-objective parameter optimization for the cross-sectional deformation of DRRT in RDB was performed by using the established model and NSGA-II algorithm. The interaction of responses was revealed and the value range of each response in the space of Pareto optimal solutions was determined. It can be observed that there is always an evident conflict between SDR and WDO in the space of Pareto optimal solutions. By using this optimization method, the absolute values of SDR and WDI were significantly reduced—by 13.17% and 17.97%, respectively—compared with those before optimization, while WDO just increase only a little.

Synthesis of circular and triangular gold nanorings with tunable optical properties.

This communication describes a robust wet-chemical synthetic strategy for the preparation of monodispersed circular and triangular gold nanorings. The localized surface plasmon resonance of the nanorings can be tuned by controlling the outer diameter and ridge thickness of the nanorings.

Study on the ridge grooves deformation of double-ridged waveguide tube in rotary draw bending based on analytical and simulative methods

Cross sectional deformation of double-ridged waveguide tube easily occurs in rotary draw bending due to its structural features of hollowness, thin-wall and shape complexity. Particularly, the ridge grooves deformation would largely affect the transmission characteristics of double-ridged waveguide tube. Thus, using plasticity deformation theory, an analytical method to investigate the ridge grooves deformation is proposed, in which the ridge grooves deformation is considered to be resulted from three parts of deformation, including flange sagging, web deflection and variation of flange width. Then, the analytical method is verified by a FE model from various viewpoints. Finally, the contribution of every part to the ridge grooves deformation under different conditions is analyzed combining analytical and simulative methods. The results show that: (1) The contribution of flange sagging to the width deformation of outer and inner ridge grooves is usually far small and can be omitted. The web deflection results in the decrease of width deformation of outer ridge groove, but the variation of flange width increases that. The web deflection and variation of flange width all lead to the increase of width deformation of inner ridge groove. (2) With the increase of bending angle, the width deformation of outer ridge groove changes little while the absolute value of width deformation of inner ridge groove increases. When the bending radius decreases, the absolute value of width deformation of outer and inner ridge grooves all increase. With the increase of core number, the width deformation of outer ridge groove changes from shrinking to widening while there is no change for the width deformation of inner ridge groove.

Influence of different mandrels on cross-sectional deformation of the double-ridge rectangular tube in rotary draw bending process

Cross-sectional deformation of the double-ridged rectangular tube inevitably occurs in the rotary draw bending process. It has serious effect on the characteristic of microwave transmission and restricts the quality and performance of tube. Different mandrels play different roles in the bending process, so the rigid and polyvinyl chloride (PVC) mandrels are applied in the E-typed and H-typed rotary draw bending of double-ridged rectangular tube to study their influence on the cross-sectional deformation. Based on the platform of ABAQUS/Explicit, the three-dimensional finite element models for E-typed and H-typed rotary draw bending of H96 brass double-ridged rectangular tube with rigid and PVC mandrels have been established and validated by experiment. Results show that whether in the E-typed or H-typed bending, the PVC mandrel has better inhibitory effect on the cross-sectional long-side deformation δL, short-side deformation δW, and spacing deformation between the bottom of ridge grooves δw of the tube. And the PVC mandrel can be more helpful to reduce the width deformation of ridge grooves of the tube in H-typed bending. The rigid mandrel can restrain the width expansion deformation of outer ridge groove of the tube more effectively in E-typed bending. However, whether using the rigid or PVC mandrel, the width shrinkage deformation of inner ridge groove of the tube in E-typed bending is less affected by the type of mandrels. And the width of two ridge grooves on sidewalls of the tube in H-typed bending also has the obvious shrinkage deformation.

The X-Ray Crystal Structure of the Keratin 1-Keratin 10 Helix 2B Heterodimer Reveals Molecular Surface Properties and Biochemical Insights into Human Skin Disease

Keratins 1 (K1) and 10 (K10) are the primary keratins expressed in differentiated epidermis. Mutations in K1/K10 are associated with human skin diseases. We determined the crystal structure of the complex between the distal (2B) helices of K1 and K10 to better understand how human keratin structure correlates with function. The 3.3 Å resolution structure confirms many features inferred by previous biochemical analyses, but adds unexpected insights. It demonstrates a parallel, coiled-coil heterodimer with a predominantly hydrophobic intermolecular interface; this heterodimer formed a higher order complex with a second K1-K10-2B heterodimer via a Cys401K10 disulfide link, although the bond angle is unanticipated. The molecular surface analysis of K1-K10-2B identified several pockets, one adjacent to the disulfide linkage and conserved in K5-K14. The solvent accessible surface area of the K1-K10 structure is 20-25% hydrophobic. The 2B region contains mixed acidic and basic patches proximally (N-terminal), whereas it is largely acidic distally (C-terminal). Mapping of conserved and nonconserved residues between K1-K10 and K5-K14 onto the structure demonstrated the majority of unique residues align along the outer helical ridge. Finally, the structure permitted a fresh analysis of the deleterious effects caused by K1/K10 missense mutations found in patients with phenotypic skin disease.

Impact of springback on the cross-sectional deformation of H96 brass double-ridged rectangular tube in E-typed rotary draw bending

Cross-sectional deformation is one of the critical factors that affect the forming accuracy of double-ridged rectangular tube (DRRT) in E-typed rotary draw bending (RDB). In the forming process, springback is inevitable and it has a direct impact on the cross-sectional deformation. Based on ABAQUS platform, three-dimensional finite element (3D-FE) models for bending and springback of H96 brass DRRT in E-typed RDB were established. With the models, the impact of springback on the cross-sectional deformation was studied. Results show that after springback, the deformation of cross-sectional height and two ridge grooves spacing increase in cores-support zone while decrease in no-cores-support zone. The impact of springback on width deformation is not significant. The maximum values of cross-sectional height deformation and two ridge grooves spacing deformation from 0° to 30° become larger after springback, while the change rules of these two from 30° to 90° are reversed. What’s more, the maximum value of width deformation from 0° to 60° becomes larger after springback while that of outer ridge groove width deformation becomes smaller, and these two from 60° to 90° both have the reversed change rules as well.

Construction methodology for lip surface of a submerged inlet

The design of submerged inlet remains a challenge as the design involves both the fuselage and the inlet internal duct. The inlet lip surface blending needs to meet stringent conditions, which vary considerably from fore lip to aft lip. The need for high aerodynamics performance also adds to the difficulty of the design process. In this paper a methodology is presented by which the inlet lip surface is mapped to a rectangular grid system which is topologically similar to the surface to be blended. A number of key grid lines can be identified, through the construction of the key curves, which are outer profile curve, inner profile curve, ridge curve and multiple blending curves. Furthermore, lip surface can be blended through the application of sweeping algorithm. A detailed example as presented in this paper illustrates the whole design procedure and technique to transform the design of a spatial curve into that of two planar curves on two developable surfaces. The above method facilitates the design of spatial curves for outer profile curve and ridge curve. The lip surface blending leaves a number of design parameters which can be manipulated to offer the scope of optimization of the aerodynamic performance in the subsequent CFD phase of the development. The numerical simulation conducted indicates that actual performances meet the design objectives well, which demonstrates the effectiveness of this design methodology.

The morphology and evolution of tidal sand bodies in the macrotidal Gulf of Khambhat, western India

Tidal sand bars and tidal sand ridges are extensively developed in the macrotidal Gulf of Khambhat, offshore western India. The inner and outer regions of the gulf are characterised by the development distinct tidal sand bodies with discrete geometries and dimensions. The outer gulf ridges are long, narrow, curvilinear and several metres high (∼20 m). They are asymmetric in cross-section and migratory in nature, forming ‘ribbon’ like sand bodies separated by tidal channels. Active dunes on these ridges indicate the presence of sand and their orientation parallel to palaeo-shorelines supports a tidal origin. In contrast to the outer gulf tidal sand ridges, sand bars associated with macrotidal estuaries flanking the Gulf of Khambhat typically have an elongate to diamond shape and are only hundreds of metres in width and a few kilometres length. These tidal sand bars occur in the estuary mouths and within the tidally influenced fluvial reaches of the rivers flowing into the gulf. The height of these sand bars is in the range ∼1–3 m. Due to high tidal ranges and bi-directional flow the sand bars do not develop significant height and are formed between the mutually evasive ebb and flow channels. Their bi-directional foresets and the presence of abundant mud drapes associated with the dunes within in-channel sand bars indicate a tidal origin.The Gulf of Khambhat acquired the present configuration in the last few thousand years since the Pleistocene sea-level lowstand (last glacial maximum, ∼18 ka) when the entire continental shelf was subaerially exposed and rivers down-cut into the coastal plain. With increasing sea-level rise, the exposed shelf was drowned, flooding parts of the Modern western Indian peninsula, and large tidal sand ridges formed in the outer gulf. After the fall of sea-level at 2 ka the gulf acquired the Modern configuration with multiple estuaries on both coastlines, rivers supplied the embayment with sandy sediment, and tidal sand bars formed in the Modern estuaries.Quantitative data gathered from the Modern Gulf of Khambhat indicates that for the P50 case, a vertical drill hole will encounter tidal sand bodies (ridges and bars combined) of approximate dimensions 1700 m long, 470 m wide and 1.5 m high, with a spacing of 400 m. In subsurface hydrocarbon reservoirs, where data is sparse and only limited amount of core is available, this quantitative dataset can be useful to constrain subsurface geocellular models. Also, the overall geometry, distribution and aspect ratio of the tidal sand ridges and tidal sand bars can be used to identify ancient counterparts through seismic geomorphology or in core.

Rediagnosis of <i>Onigocia grandisquama</i> (Actinopterygii: Perciformes: Platycephalidae) and Comparison with Congeners

A platycephalid fish, Onigocia grandisquama ( Regan, 1908 ) is rediagnosed based on 52 specimens, including the holo-type, from the Indo-West Pacific. Geographic variation in the species was recognized in the number of pectoral-fin rays, the first example of such variation in fin ray counts in the Platycephalidae. The species displays wide intraspecific variation in the numbers of lachrymal, preocular, suborbital, and pterotic spines, with values for the first two overlapping with those of the very similar Onigocia spinosa (Temminck and Schlegel, 1843), making it difficult to separate the two. Onigocia grandisquama can be distinguished from O. spinosa, as well as from Onigocia macrocephala (Weber, 1913) and Onigocia macrolepis (Bleeker, 1854), which share with O. grandisquama an ocular flap on the posterior part of the eye, in lacking spines on the inner, middle, and/or outer ridges of the lachrymal. The generally greater number of pterotic spines also helps to separate O. grandisquama from its three congeners.

Growth requirements of different potato cultivars

A field trial with four potato cultivars (Faluka, Manitou, Madeleine and Stirling) was conducted in two consecutive years (2012 and 2013) at a laboratory field of Biotechnical Faculty in Ljubljana. The aim of the study was to evaluate different requirements of the selected cultivars in regard to the ridge and tuber cluster. The following parameters were defined and monitored: area of the form surrounding the tubers (ellipse), cross-sectional area of the ridge, vertical and horizontal tuber span in the ridge, the length of semi-axes (a) and (b) of the ellipse, minimum distance of tubers and ellipse from the outer ridge side. The results of 2012 trial indicated that the minimal ellipse method defining the ellipse was not satisfactory as statistical significance was limited due to a large volume of vacant space in the ridge not occupied by potato tubers. Therefore, the mathematical model was upgraded in 2013 and a physical parameter (tuber mass) was incorporated in the equation to better depict the tuber cluster. The trials were designed as a randomized block with five repetitions. The largest ellipse, horizontal tuber span in the ridge and the longest semi-axis (a) were recorded for the cv. Manitou resulting in the highest yield. However, no statistical differences were recorded in the horizontal tuber span, the length of the semi-axis (a) or cross-sectional area of the ridge among cultivars analysed. It was determined that different cultivars require specific growth space in the potato ridge. Moreover, the newly developed method proved efficient for determining growth requirements of potato tubers in the ridge.