Prism Width Research Articles

The mean pressure distribution on the free end of a square prism

In this experimental study, the mean pressure distribution was measured on the free end of a surface-mounted finite-height square prism for different aspect ratios, incidence angles, and boundary layer thicknesses. The Reynolds number based on the width of the prism was kept constant at Re = 6.5 × 104, the aspect ratio of the prism was changed from AR = 1 to 11, and the incidence angle was varied in small increments from α = 0° to 45°. The thickness of the boundary layer on the ground plane relative to the prism width was either δ/D = 0.8 or δ/D = 2.6, representing a thin or thick boundary layer. When the prism was oriented at α = 0°, distinct mean pressure distributions were observed for prisms nearly or completely immersed in the boundary layer, and also for the very slender high-aspect ratio prisms. The mean normal force coefficient steadily increased with the aspect ratio but its value decreased in the presence of the thicker boundary layer. When the prism was oriented at α = 45°, strong pressure gradients were encountered near the leading edges for prisms nearly or completely immersed in the boundary layer, and the conical vortex angles increased with aspect ratio. For intermediate aspect ratios, these pressure gradients weakened and the vortex angles became insensitive to AR. When the incidence angle was between 0° and 45°, the asymmetric mean pressure distribution meant that the conical vortices were located at different angles. The position of the conical vortex located more centrally above the free end was more sensitive to changes in aspect ratio. The influence of the boundary layer on the vortex angles was more pronounced for smaller aspect ratios. In addition, the behaviour of the normal force coefficient with incidence became more complex for higher aspect ratios.

Experimental observation of flow-induced vibrations of a transversely oscillating D-section prism

Fluid–structure interactions of non-circular prisms are of significance from a scientific and practical viewpoint. In this paper, we present a new experimental observation of flow-induced vibrations and associated spectral characteristics of a transversely oscillating D-section prism at an angle of attack α varying from 0° to 180°, where α = 0° and 180° represent the configuration with the upstream curved and flat part, respectively. The Reynolds number range is 530–9620, and the reduced velocity range is 1–32, based on the projected prism width in the crossflow direction. The mass ratio of the prism is 11.35, and the structural damping ratio in still water is 0.0036. Based on the response amplitudes and spectral traits, the D-prism exhibits the typical vortex-induced vibration (VIV) at α = 0°–30°, the first transition response at α = 45°–60°, the small-amplitude VIV response at α = 105°–135°, the second transition response at α = 150°–165°, the combined VIV-galloping response at α = 90°, and the pure galloping at α = 75° and 180°. The second transition response between low- and high-amplitude branches is found to be hysteretic and intermittent. Flow physics behind the D-prism responses are further elucidated by the wake patterns based on a high-speed camera and the flow velocity spectra downstream of the prism.

Study of the human enamel prisms maturation nature in different periods of postpartum ontogenesis by atomic force microscopy

It is necessary to study the human enamel prisms size at different periods of postpartum ontogenesis by atomic force microscopy. The study involved 94 males which were divided into groups by age: 15-20, 21-30, 31-40, 41-50, 51-60 years old, each examined male had one 3.8 or 4.8 tooth removed (from the fracture line in the region angle of the mandible, according to orthodontic indications) for medical reasons. The shape, roughness, length and width of the enamel prisms were studied in the Image Analysis NT-VDT program according to the method of Omsk State Medical University. The enamel prisms structure at all ages has a regular, ordered shape with 6-sided and 7-sided figures. The most constant structure occurs at the age group of 41-50, 51-60 years. The fastest enamel prisms growth occurs in the direction that increases the prism length at all ages. Growth on a plane which increases the prism width is slow at 41-50 years. It is catching up with the growth rate of enamel prisms in length at 51-60 years old. Enamel prisms at 15-20, 21-30 years old stretch faster in the horizontal direction. In maturation process, due to correct and harmonious growth, enamel prisms are timely modified from pyramidal form in the early postpartum period to a prismatic form in the late postpartum period of ontogenesis.

Justification of dump parameters in conditions of high water saturation of soils

The object of research is the stability parameters of the massif of a single-tier dump of soft overburden rocks with a flooded slope when it is formed by a dragline excavator. One of the most problematic areas is determining the safe distance of the dragline excavator from the upper edge of the slope in the conditions of the formation of a single-tier dump of soft overburden rocks, flooded with water.The calculation of the width of the prism of possible shift was carried out using the Rocscience Slide software, which, taking into account the parameters of the slope and the physical and mechanical properties of the rock mass, automatically restores a number of curved sliding surfaces for individual safety factors. The obtained data were processed using the Microsoft Excel software, thanks to which, by the least squares method, graphs of the functions of the possible shift prism width from the height of the tier of a dump of soft overburden rocks and the level of its flooding were constructed.For the conditions of the formation of a single-tier dump of soft rocks of overburden with a height of 40–100 m and a flooding level of 0–30 m, the width of the prism of a possible shift was calculated for sliding surfaces with a safety factor of 1 and 1.2. These values are, respectively, 0–85.9 m and 0–122.6 m within the established calculation limits and depending on the method of constructing curved surfaces. The distance between the points of intersection of the horizontal surface of the tier with curved sliding surfaces with a safety factor of 1 and 1.2 is 16–52.5 m. The dependences of the width of the prism of possible shift (a) on the height of the tier of a dump of soft overburden rocks (Ho) and its level flooding (Hw), taking into account the physical and mechanical properties of the dumped mountain range, including saturated with water. The minimum deviation from the initial value of the coordinates of the points is achieved when setting the second-degree polynomial as the trend line for the function a=f(Hw), and for a=f (Hо) – a straight line.The obtained data for calculating the parameters of the possible shift prism suggest the possibility of forming a single-tier dump of soft overburden rocks with a height of 40–60 m with unloading of rock mass into the worked-out space and 70–100 m with loading the unstable part of the slope with an EK-11/70 excavator-dragline (Novokramatorsk Machine-Building plant, Ukraine).

Effect of side walls on flow around prisms

Two-dimensional laminar flow around three side-by-side rectangular prisms placed between two parallel walls is numerically investigated at a Reynolds number Re = 100. The cross-sectional aspect ratio of each prism is b/h = 3, where b and h are the prism width and height, respectively. The gap spacing (g) between the two adjacent prisms and between the wall and the outer prism is varied from g* (= g/h) = 0.8 to 3.4. The focus is given on the influence of g* on flow structures, Strouhal number (St), and fluid forces. Three distinct flow regimes are identified, namely single vortex street (0.8 ≤ g* < 1.1), twin vortex streets (1.1 < g* < 2.1), and triple vortex streets (2.1 < g* ≤ 3.4). Lift forces on the outer prisms are attractive for single vortex street and repulsive for twin and triple vortex streets. The St being identical for the three prisms exponentially declines from 0.39 to 0.18 with g* increasing from 0.8 to 3.4. Fluctuating lift and time-mean drag also shrink with increasing g*, time-mean drag becoming higher for the middle prism than for the outer prisms. Empirical relations of St and forces are obtained as a function of g*.

Intravesicular Phosphatase PHOSPHO1 Function in Enamel Mineralization and Prism Formation.

The transport of mineral ions from the enamel organ-associated blood vessels to the developing enamel crystals involves complex cargo packaging and carriage mechanisms across several cell layers, including the ameloblast layer and the stratum intermedium. Previous studies have established PHOSPHO1 as a matrix vesicle membrane-associated phosphatase that interacts with matrix vesicles molecules phosphoethanolamine and phosphocholine to initiate apatite crystal formation inside of matrix vesicles in bone. In the present study, we sought to determine the function of Phospho1 during amelogenesis. PHOSPHO1 protein localization during amelogenesis was verified using immunohistochemistry, with positive signals in the enamel layer, ameloblast Tomes' processes, and in the walls of ameloblast secretory vesicles. These ameloblast secretory vesicle walls were also labeled for amelogenin and the exosomal protein marker HSP70 using immunohistochemistry. Furthermore, PHOSPHO1 presence in the enamel organ was confirmed by Western blot. Phospho1−/− mice lacked sharp incisal tips, featured a significant 25% increase in total enamel volume, and demonstrated a significant 2-fold reduction in silver grain density of von Kossa stained ground sections indicative of reduced mineralization in the enamel layer when compared to wild-type mice (p < 0.001). Scanning electron micrographs of Phospho1−/− mouse enamel revealed a loss of the prominent enamel prism “picket fence” structure, a loss of parallel crystal organization within prisms, and a 1.56-fold increase in enamel prism width (p < 0.0001). Finally, EDS elemental analysis demonstrated a significant decrease in phosphate incorporation in the enamel layer when compared to controls (p < 0.05). Together, these data establish that the matrix vesicle membrane-associated phosphatase PHOSPHO1 is essential for physiological enamel mineralization. Our findings also suggest that intracellular ameloblast secretory vesicles have unexpected compositional similarities with the extracellular matrix vesicles of bone, dentin, and cementum in terms of vesicle membrane composition and intravesicular ion assembly.

Intrinsic features of flow past three square prisms in side-by-side arrangement

An investigation on the flow around three side-by-side square prisms can provide a better understanding of complicated flow physics associated with multiple, closely spaced structures in which more than one gap flow is involved. In this paper, the flow around three side-by-side square prisms at a Reynolds number$Re=150$is studied systematically at$L/W=1.1{-}9.0$, where$L$is the prism centre-to-centre spacing and$W$is the prism width. Five distinct flow structures and their ranges are identified, viz. base-bleed flow ($L/W&lt;1.4$), flip-flopping flow$(1.4&lt;L/W&lt;2.1)$, symmetrically biased beat flow$(2.1&lt;L/W&lt;2.6)$, non-biased beat flow$(2.6&lt;L/W&lt;7.25)$and weak interaction flow$(7.25&lt;L/W&lt;9.0)$. Physical aspects of each flow regime, such as vortex structures, vortex dynamics, gap-flow behaviours, shedding frequencies and fluid forces, are discussed in detail. A secondary (beat) frequency other than the Strouhal frequency (primary frequency) is observed in the symmetrically biased and non-biased beat flows, associated with the beat-like modulation in$C_{L}$-peak or amplitude, where$C_{L}$is the lift force coefficient. Here we reveal the generic and intrinsic origin of the secondary frequency, establishing its connections with the phase lag between the two shear-layer sheddings from the two sides of a gap. When the two sheddings are in phase, no viscous force acts at the interface (i.e. at the centreline of the gap) of the two sheddings, resulting in the largest fluctuations in streamwise momentum, streamwise velocity and pressure; the maximum$C_{L}$amplitude thus features the in-phase shedding. Conversely, when the two sheddings are antiphase, a viscous force exists at the interface of the two sheddings and restricts the momentum fluctuation through the gap, yielding a minimum$C_{L}$amplitude. When the phase relationship between the two sheddings changes from in phase to antiphase, the extra viscous force acting at the interface becomes larger and causes the$C_{L}$amplitude to change from a maximum to a minimum.

The effect of incidence angle on the mean wake of surface-mounted finite-height square prisms

The mean wake of a surface-mounted finite-height square prism was studied experimentally in a low-speed wind tunnel to explore the combined effects of incidence angle (α) and aspect ratio (AR). Measurements of the mean wake velocity field were made with a seven-hole pressure probe for finite square prisms of AR=9, 7, 5 and 3, at a Reynolds number of Re=3.7×104, for incidence angles from α=0° to 45°. The relative thickness of the boundary layer on the ground plane, compared to the prism width, was δ/D=1.5. As the incidence angle increases from α=0° to 15°, the mean recirculation zone shortens and the mean wake shifts in the direction opposite to that of the mean lift force. The downwash is also deflected to this side of the wake and the mean streamwise vortex structures in the upper part of the wake become strongly asymmetric. The shortest mean recirculation zone, and the greatest asymmetry in the mean wake, is found at the critical incidence angle of αcritical≈15°. As the incidence angle increases from α=15° to 45°, the mean recirculation zone lengthens and the mean streamwise vortex structures regain their symmetry. These vortices also elongate in the wall-normal direction and become contiguous with the horseshoe vortex trailing arms. The mean wake of the prism of AR=3 has some differences, such as an absence of induced streamwise vorticity near the ground plane, which support its classification as lying below the critical aspect ratio for the present flow conditions.

Mammalian enamel maturation: Crystallographic changes prior to tooth eruption.

Using the distal molar of a minipig as a model, we studied changes in the microstructural characteristics of apatite crystallites during enamel maturation (16-23 months of postnatal age), and their effects upon the mechanical properties of the enamel coat. The slow rate of tooth development in a pig model enabled us to reveal essential heterochronies in particular components of the maturation process. The maturation changes began along the enamel-dentine junction (EDJ) of the trigonid, spreading subsequently to the outer layers of the enamel coat to appear at the surface zone with a 2-month delay. Correspondingly, at the distal part of the tooth the timing of maturation processes is delayed by 3-5 month compared to the mesial part of the tooth. The early stage of enamel maturation (16-20 months), when the enamel coat is composed almost exclusively of radial prismatic enamel, is characterized by a gradual increase in crystallite thickness (by a mean monthly increment of 3.8 nm); and an increase in the prism width and thickness of crystals composed of elementary crystallites. The late stage of maturation (the last two months prior to tooth eruption), marked with the rapid appearance of the interprismatic matrix (IPM) during which the crystals densely infill spaces between prisms, is characterized by an abrupt decrease in microstrain and abrupt changes in the micromechanical properties of the enamel: a rapid increase in its ability to resist long-term load and its considerable hardening. The results suggest that in terms of crystallization dynamics the processes characterizing the early and late stage of mammalian enamel maturation represent distinct entities. In regards to common features with enamel formation in the tribosphenic molar we argue that the separation of these processes could be a common apomorphy of mammalian amelogenetic dynamics in general.

Effects of Dipole and Quadrupole Modes on the Switchable Total Transmission and Reflection in an Array of Rectangular Silver Prisms

Using an array of rectangular silver prisms, we numerically demonstrated that close to 100% transmission and reflection of the electromagnetic wave can be switched by slightly changing the incident wavelengths of less than 10 nm. The calculations showed that the resonance wavelengths are associated with the coherent dipole coupling among nanoparticles, and similar phenomena can also be achieved when the quadrupole mode of the metal nanoparticles is excited. While the change from total transmission to total reflection can be obtained relatively easier when the dipole mode is excited, the difference of the resonance wavelengths between the total transmission and reflection is larger. At the resonance wavelength of quadrupole excitation, the change between the total transmission and the reflection is very sharp and shows a Fano-shaped spectral profile; however, achieving close to 100% transmission and reflection is challenging. We studied the effects of prism width, height, and interparticle distance on the ...

What 2‐D multichannel seismic and multibeam bathymetric data tell us about the North Sumatra wedge structure and coseismic response

AbstractRecent large earthquakes have prompted studies to reevaluate seismicity and rupture propagation behavior along the world's major subduction margins. Our study area covers the entire fore arc from northwest of northern Sumatra to west of Simeulue Island, the southern portion of the 2004 tsunamigenic earthquake rupture zone. The accretionary prism width is up to ~180 km, water depths between ~4.5 km near the Sunda Trench and &lt;1 km on fore‐arc high. The wedge consists of a steep outer slope (5–12°), a plateau ~100–120 km wide with anticlinal folds spaced 2–15 km apart, and a steep inner slope adjacent to the Aceh Basin. Analysis of seismic profiles and bathymetry reveal three main structural zones consistent along‐strike, from the trench landward: (1) predominantly landward vergent folds, (2) mixed vergent folds, and (3) predominantly seaward vergent folds. This paper uses those zones to propose a geometry of an underlying rigid backstop. This backstop is seaward dipping and extends from under the Aceh Basin to beneath the mixed vergence zone. A dynamic backstop possibly exists seaward of the rigid backstop and is responsible for the steep slope of the outer prism. Indurated accreted sediments form the landward vergence zone. Along with the possible dynamic backstop beneath the outer wedge, and the rigid backstop in the inner wedge, all behave as a solid block coseismically. This block allows great earthquake rupture to propagate farther seaward toward the Sunda Trench, with resultant hazardous tsunamigenic potential.

Experimental characterization of flow field around a square prism with a small triangular prism

The characteristics of the flow field around a square prism containing a small triangular prism upstream were investigated by measuring lift and drag and visualizing the flow field through particle image velocimetry. Experimental parameters included triangular prism-to-square prism width ratio (H/B, H and B are side lengths of the triangular and square prisms, respectively) and triangular prism-to-square prism gap ratio (G/B, G is the gap distance between the triangular and square prisms). The drag reduction rate of the square prism increased and then decreased with increasing G/B at a constant H/B but increased with increasing H/B at a constant G/B. The maximum drag reduction rate was 78.5% at H/B = 0.6 and G/B = 1.5. The width and gap ratios also minimally affected the lift reduction rate of the square prism, with an average value of 52.4%. Stagnation regions were further observed upstream and downstream of the square prism.

Mitosis in Secretory Ameloblasts

Our objective is to test the dictum that secretory ameloblasts cannot divide. Dental biology textbooks often present this idea without citation or evidence; its source seems to be studies of rodent incisors from the 1960's. However, rodent incisors are ever‐growing, and not acceptable models for enamel epithelia in other mammals. There are two reasons to expect that ameloblasts divide. First, recent studies show that tensile forces induce mitosis in epithelia, and enamel epithelia likely undergo tension as enamel is deposited and the surface area of the growing crown expands. Second, we now know that ameloblasts are subject to the same biorhythms that synchronize proliferation of osteoblasts. If ameloblast division is also coordinated by the brain and occurs at night, it is unlikely to have been observed since most experimental protocols occur in daylight.To test the hypothesis, we first measured enamel area from surface and enamel‐dentine junction in Saimiri sciureus tooth sections. We also measured enamel rod width at both sites, as a proxy for ameloblast width. We found an average 9% greater area at the tooth surface, but no difference in enamel prism width. We also searched for mitotic figures in tooth buds of perinatal Saguinus spp. with random times of death, but found none. In conclusion, increasing tooth surface area from deep to superficial and no change in cell size suggests that ameloblast mitosis is likely. However, we did not find any mitotic figures, possibly because of sample size and lack of control over time of death.

Forearc structure and morphology along the Sumatra‐Andaman subduction zone

AbstractThe Sunda subduction margin, the location of recent magnitude 8–9 megathrust earthquakes, is characterized by major changes in prism and forearc morphology and structure along its 5000 km length. On the Sumatra‐Andaman section, measurements of prism width and surface slope (α) indicate along‐strike segments, inclu1ding abrupt changes, of prism morphology: (1) a narrow and steep prism between Burma and the Andamans; (2) broad with an averaged gentle slope in the Andamans, Nicobars, and North Sumatra; (3) steep and narrow in Central Sumatra; and (4) wider and less steep offshore South Sumatra, decreasing in width to West Java. Prism width varies from ~90 to 180 km and average surface slope from ~1 to 3° with a strong inverse correlation between width and slope, also observed globally. The prism deviates from typical taper geometry in parts of the margin, notably offshore North Sumatra where it is characterized by a steep toe and broad plateau. Along‐strike changes in morphology are strongly linked to input sediment thickness. Sections of the prism toe represent key global examples of unusual landward vergent thrusting. These sections correspond to a thick sediment input and to a wide prism with shallow surface slope. A low basal shear stress or backstop mechanism may drive this style of faulting. Prism morphology and structure appear to be driven predominantly by input sediment thickness linked to oceanic basement topography, with sediment properties, plate smoothness, and orthogonal subduction rate and obliquity also contributing, and no clear role of plate age or dip.

분리된 분할판에 의한 정방형주의 항력감소

Abstract: The Characteristics of the drag reduction of a square prism having a detached splitter plate at the wake side were investigated by measuring of lift and drag on the square prism. The experimental parameters were the width ratios(H/B=0.5~1.5) of splitters to the prism width and the gap ratios (G/B=0~2)between the prism and the splitter plate. As the results the amplitude of the lift on the square prism havinga detached splitter plate was remarkably decreased by comparison with the prototypical square prism. The drag reduction rate of the square prism was increased with H/B in case of the same G/B, and was increased and decreased with G/B in case of the same H/B. The maximum drag reduction rate was represented by 24.2% at H/B=1.5 and G/B=0.5. Key words: Drag reduction, Separated flow, Unsteady flow, Square prism, Splitter plate †교신저자(경상대학교 기계시스템공학과․해양산업연구소, E-mail: rokid@gnu.ac.kr, Tel: 055-772-9103)1 경상대학교 기계시스템공학과, E-mail: yoon21y@naver.com, Tel: 010-3848-62262 경상대학교 기계시스템공학과, E-mail: bii206@nate.com, Tel: 010-9798-95353 경상대학교 기계시스템공학과, E-mail: coo1702@nate.com, Tel: 010-3705-94614 경상대학교 기계시스템공학과, E-mail: ocs1419@naver.com, Tel: 010-8423-4503

Advances in mollusc sclerochronology and sclerochemistry: tools for understanding climate and environment

This Special Issue of Geo-Marine Letters compiles papers on marine, estuarine and freshwater mollusc shells as recorders of environmental and climatic conditions. Considering that many past studies have differentiated geochemical investigations from sclerochronological investigations, we propose that the sub-discipline term “sclerochemistry” be used when geochemical investigations are undertaken. This issue starts with two review papers that discuss the importance of physiology or vital effects on both sclerochronology and sclerochemistry. Several sclerochemical calibration studies on modern specimens of both bivalves and gastropods are presented (including δ18O, Mg/Ca, Sr/Ca and Ba/Ca), which illustrate the usefulness and difficulties associated with using these proxies. Studies on fossil mollusc shells are also provided, with one study that uses Pliocene scallop shells to understand past ocean circulation and another that addresses the problem of diagenesis. Finally, a sclerochronological study of crystal prism width across the shell is presented. This Special Issue demonstrates that many elemental and isotopic proxies contained in mollusc shells are complex. In spite of these complexities, environmental and climatic conditions can be extracted for use in palaeoclimatic and palaeoenvironmental research.

Does prism width from the shell prismatic layer have a random distribution?

A study of the distribution of the prism width inside the prismatic layer of Unio tumidus (Philipsson 1788, Diss Hist-Nat, Berling, Lundæ) from Lake Neuchâtel, Switzerland, has been conducted in order to determine whether or not this distribution is random. Measurements of 954 to 1,343 prism widths (depending on shell sample) have been made using a scanning electron microscope in backscattered electron mode. A white noise test has been applied to the distribution of prism sizes (i.e. width). It shows that there is no temporal cycle that could potentially influence their formation and growth. These results suggest that prism widths are randomly distributed, and related neither to external rings nor to environmental constraints.

SUPPRESSION OF FLUID FORCES ACTING ON TWO SQUARE PRISMS IN A TANDEM ARRANGEMENT BY PASSIVE CONTROL OF FLOW

The suppression of fluid forces acting on two square prisms in a tandem arrangement in which a flow approaching the upstream prism was controlled by a thin flat plate was examined, with variation in spacing between the plate and the upstream prism. The width of the plate was one-ninth of the prism width. The position of the control plate was varied from the front surface of the upstream prism to 2·25 times the prism width in the upstream direction, and the position of the downstream prism was varied from the rear surface of the upstream prism to 10 times the prism width in the downstream direction. A dramatic decrease in fluid forces acting on both prisms was observed for a certain range of control plate positions. For such optimum positions of the control plate, the shear layers that separated from the control plate attached near the edges of the front surface of the upstream prism and each shear layer bifurcated into two layers, one part of the shear layers making a quasi-steady recirculating region between the control plate and the upstream prism, and the other part separating from the leading edges and attaching again to the side-surfaces of the upstream prism. When the control plate was placed with spacings S/W=1·50∼1·90 (S: spacing between the control plate and the upstream prism, W: width of the prism), the above-mentioned flow pattern appeared, and the fluid forces and vortex shedding of the upstream prism were almost completely suppressed. Also, the upstream prism was found to be insensitive to the existence of the downstream prism when the latter was located downstream, approximately six or more times the prism width.

Unique enamel phenotype associated with amelogenin gene (AMELX) codon 41 point mutation.

Different mutations in the amelogenin gene (AMELX) result in the markedly different enamel phenotypes that are collectively known as amelogenesis imperfecta (AI). We hypothesize that unique phenotypes result from specific genetic mutations. The purpose of this study was to characterize the enamel compositional and structural features associated with a specific AMELX mutation in three families with X-linked AI. We performed mutational analysis by amplifying AMELX exons and sequencing the products. Permanent and primary affected (N = 6) and normal (N = 3) teeth were collected and examined by light, scanning, and transmission electron microscopy. Enamel proteins were evaluated by immunolocalization of amelogenin and amino acid analysis. AI-affected individuals all shared a common AMELX point mutation (C to A change at codon 41). The dental phenotypic findings were remarkably consistent in all affected individuals. The AI enamel was opaque, with numerous prism defects or holes encompassing the entire prism width. Affected crystallites appeared more radiolucent and morphologically less uniform, compared with that of normal enamel. Immunogold labeling with anti-amelogenin antibodies localized amelogenin to the crystallites but not to the inter-crystalline spaces. No immunogold labeling was seen in normal enamel. There was an increased and amelogenin-like protein content in AI enamel (0.95%) compared with normal enamel (0.13%). We conclude that this codon 41 C to A missense point mutation, in a highly conserved region of the AMELX gene, results in a remarkably consistent phenotype.

Observations on stria morphology in the lateral enamel of Pongo, Hylobates and Proconsul teeth.

The enamel of certain primates (orang-utans, siamangs and the early Miocene fossil hominoid, Proconsul) occasionally contains striae of Retzius that appear distinct from those more typical of the lateral and cervical enamel of other anthropoids. These striae can be described as "S-shaped" since their contour is markedly sinuous as it passes from the enamel dentine junction (EDJ) to the tooth surface. "S-shaped" striae have never been described in the comparative literature on primate enamel and yet they may be of some phylogenetic significance. This study explores the interrelationship between four variables in the enamel of an orang-utan, a siamang and a specimen of Proconsul heseloni (from Rusinga Island, Kenya) all of which contain "S-shaped" striae. The morphological components of this form of stria have been quantified here. The four variables measured were (1) prism width; (2) the angle the prisms make to the EDJ; (3) the angle the striae of Retzius make with respect to the EDJ, and (4) the daily rate of enamel formation. Each of these four variables was measured in inner enamel close to the EDJ, in enamel mid-way between the EDJ and the enamel surface, and in outer enamel. Our aim was both to quantify the components of "S-shaped" striae and to attempt to offer a developmental explanation for the appearance of these striae in fully formed enamel. We conclude that "S-shaped" striae may be associated with regions of lateral enamel where prism width either remains constant or even reduces as the enamel surface is approached. This, together with an increase in the linear daily rate of enamel secretion towards the outer enamel, a cervical inclination in the angulation of the prisms with respect to the EDJ, and an increased angulation of the striae of Retzius to the EDJ are all features that characterize "S-shaped" striae. This description will facilitate identification and quantification of any similar striae in the enamel of other primates. It will also allow careful comparison of each of the four variables one with another which may in turn help in establishing "S-shaped" striae as developmentally homologous between species.