Vertical Tapping Research Articles

Granular medium under vertical tapping: change of compaction and convection dynamics around the liftoff threshold.

A granular medium submitted to vertical tapping reveals simultaneously compaction and convection. The two phenomena are directly coupled and their dynamics can be quantified by a characteristic compaction time and by an estimation of the convective downhill speed along the wall. A remarkable change of behavior is observed around the liftoff acceleration threshold of the whole packing, with a drastic slowing down of both dynamics below this threshold. Above it, a collective shock wave densifies the packing at each tap, whereas, below it, cumulative localized rearrangements will compact the entire system in the long time range.

Numerical model for granular compaction under vertical tapping.

A simple numerical model is used to simulate the effect of vertical taps on a packing of monodisperse hard spheres. Our results are in good agreement with an experimental work done in Chicago and with other previous models, especially concerning the dynamics of the compaction, the influence of the excitation strength on the compaction efficiency, and some aging effects. The principal asset of the model is that it allows a local analysis of the packings. Vertical and transverse density profiles are used, as well as size and volume distributions of the pores. An interesting result concerns the appearance of a vertical gradient in the density profiles during compaction. Furthermore, the volume distribution of the pores suggests that the smallest pores, ranging in size between tetrahedral and octahedral sites, are not strongly affected by the tapping process, in contrast to the largest pores which are more sensitive to the compaction of the packing.

Inverse density segregation of binary particle mixtures subjected to vertical tappings and vibration

Abstract This paper investigates the inverse density segregation of binary particle mixtures under vertical tapping and vibration. Three different sized glass and steel beads (1290, 655 and 463 μm in diameter) were used in the experiment, together with three sizes of vessels (20 cm in height, 3 cm in thickness, and 10, 5 and 3 cm in widths). It has been observed that (i) as a general rule, the smaller the particle, the sharper the segregation of heavier particles to the upper region of the bed, (ii) an appropriate fluidity of the particle bed is essential for the inverse segregation to occur, and (iii) the bed height is an important factor to determine the degree of segregation, given the other conditions.

Evaluation of bone density using cutting resistance measurements and microradiography. An in vitro study in pig ribs.

A method using cutting resistance measurements during low-speed threading for identification of various bone densities has been evaluated with regard to its precision and potential. Pig ribs were used as test samples. Differing hand pressure, minor deviation (5 degrees) from a vertical tapping direction and individual threading did not reveal any significant differences in cutting resistance values. After implants were inserted into the threaded canals, the total bone as well as trabecular and compact bone areas surrounding the implants were calculated via a computer program and using microradiographs of the bone test samples. The outcome of the cutting resistance measurements was compared with that of the microradiographic technique, and good agreement was observed between the two procedures in the ability to identify bone density. Therefore, cutting resistance measurements may in the future also be used to clinically identify bone qualities in jaws.

Etude des modalités de la mycorhization de pivots d'Eucalyptus globulusdéveloppés en clinostat

Summary The present study analyze the aptitude to the mycorrhization with Pisolithus tinctorius of tap root of seedlings of Eucalyptus globulus grown in a clinostat. Unlike the vertical tap roots developed in normal conditions, these tap roots are strongly colonized. The fungus builds an ectomycorrhiza with a dense mantle and massive intercellular structures equivalent to an Hartig net. Physiological perturbations, induced by the modification of the growth of the tap root, would be involved in the mycorrhization.

Paleoenvironments of Root Casts from the Koobi Fora Formation, Kenya

A study of fossil mots and root casts from East Turkana, Kenya, has shown them to be useful paleoenvironmental indicators. Fossil root casts were obtained from the Pleistocene, Upper Member of the Koobi Fora Formation, deposited within the East Turkana Embayment of the Lake Turkana Basin. Lithofacies and biofacies analysis of the study locality allows the discrimination of several important environments which contain root casts, notably fluvial channels and shallow lacustrine conditions. Five common root cast morphologies have been observed: 1) horizontal, planar root mats; 2) vertical or vertically branching structures; 3) horizontal or horizontally branching structures; 4) diagonally branching structures; and 5) root balls (concretionary structures). Root cast morphology is shaped both by the original root morphology and post-mortem, diagenetic development. Line transect surveys of fossil root casts reveal two striking lithofacies-root cast associations. Laminated siltstones of the shallow lacustrine environment primarily contain root mats and horizontal roots, whereas sandstone-conglomerates of the fluvial paleochannels contain predominantly vertical and diagonal root casts, with no root mats. Studies of plant associations in the Lake Turkana area, and work on modern root morphologies suggest a probable explanation for these associations. In arid environments, water availability is a dominant factor in root morphology. Plants growing along intermittent streams or floodplains must frequently rely on perched water bodies or deeper phreatic water, therefore sending out long, vertical tap roots to take advantage of this resource. Plants living in permanent, shallow lacustrine environments or other areas where phreatic water is quite shallow have no such requirement, since their roots are nearly continuously immersed in ground water; during floods the plant stalk itself is subaqueous. The roots of these plants tend to extend laterally in thin mats over large areas. Thus, a study of root cast morphologies may allow for an assessment of paleogroundwater conditions in nonmarine sediments.

The dry‐packing of columns in liquid chromatography

AbstractThis contribution comprises two parts, the one covering some variables in the dry‐packing of columns for liquid chromatography, the other the use of an automatic dry‐packer in liquid chromatography. A high‐pressure stainless steel column was dry‐packed using a 20‐44 μm size, irrregularly shaped, silica gel support. It was found that, when support was added in discrete amounts, lateral tapping produced a column of higher efficiency (HETP = 0.69 mm) than was the case for vertical tapping (HETP = 1.37 mm). Simultaneous vertical and lateral tapping produced an intermediate result. Bulk filling of the column followed by tapping was inferior to adding support in discrete amounts. An apparatus constructed to perform the vertical and lateral tapping operations automatically confirmed the above conclusions. It was concluded that commercially available dry‐packing apparatus do not offer the best action for packing an efficient column since they involve predominantly vertical tapping.

EFFECTS OF PLACEMENT LOCATION FOR PHOSPHORUS BANDED AWAY FROM THE SEED ON GROWTH AND UPTAKE OF SOIL AND FERTILIZER PHOSPHORUS BY FLAX

Growth chamber studies were conducted on the relative effects of various placements of NH4H232PO4 applied at 20 kg P ha−1 in a single band away from the seed on growth, and on uptake of soil and fertilizer P by flax (Linum usitatissimum L. ’Linott’) grown on two P-deficient Chernozemic soils; one calcareous, the other non-calcareous. Crop response was very sensitive to location of the placed P. Placement of the P away from, and up to 3.0 cm to the side and from 0–4.5 cm below the seed on average increased aboveground dry matter yield and P uptake of flax 8 wk after seeding by 2.3- and 2.1-fold, respectively, compared with the non-P fertilized soils. Maximum yields and P uptake, which were approximately four and three and a half times greater, respectively, than the non-P fertilized values, were achieved by placing the P no more than 1.5 cm to the side and 1.5–3.0 cm below the seed. Flax root development studies indicated that this was due largely to root development during the first few weeks being limited to a small cylinder of soil immediately surrounding the single vertical tap root. Distance of placement of P away from the seed was more critical for the calcareous soil, with crop use of the applied P being noticeably less for this soil (4.8–17.3%) than for the non-calcareous soil (18.3–40.2%).

Environmental Significance of Fossil Root Casts from Koobi Fora Formation (Pliocene-Pleistocene), East Turkana, Kenya: ABSTRACT

Roots and fossil root casts at East Turkana, Kenya, are valuable as paleo-environmental indicators. Roots are preserved within the Koobi Fora Formation as calcified concentric and nodular casts in lithologies independently interpreted as fluviodeltaic or lacustrine-coastal plain. Five common root cast types are recognized: (1) horizontal, planar root mats; (2) vertical or vertically branching root structures; (3) horizontal or horizontally branching root structures; (4) diagonally branching root structures; and (5) root clusters or balls. Root mats are usually in blocky or laminated muds. Typically, the mats extend laterally over tens of square meters, although an individual mat will be only about 5 cm thick. They appear to have grown in quiet-water lagoons. Vertical ro t structures are best developed in coarse-grained sands interpreted as fluvial channel, and secondarily in fine-grained silts believed to be interdistributary overbank deposits. They are uncommon in blocky or laminated lagoonal muds. Comparison of root morphologies among living East Turkana plants supports interpretation of the fossil associations. In arid environments water availability is a dominant factor in root morphology. Plants growing along intermittent streams or flood plains must frequently rely on perched water bodies or underground seepage, and therefore send out long vertical tap roots to take advantage of this limiting resource. Plants living within shallow reed swamps have no such requirement, as their roots are nearly continually immersed in ground water; during floods th plant stalk itself is subaqueous. The roots of these plants tend to extend laterally in thin mats over much of the lagoon. End_of_Article - Last_Page 434------------