Number Of Lamellae Research Articles

Swelling of fiber-reinforced soft tissues is affected by fiber orientation, fiber stiffness, and lamella structure.

Native and engineered fiber-reinforced tissues are composites comprised of stiff collagen fibers embedded within an extrafibrillar matrix that is capable of swelling by absorbing water molecules. Tissue swelling is important for understanding stress distributions between collagen fibers and extrafibrillar matrix, as well as for understanding mechanisms of tissue failure. The swelling behavior of fiber-reinforced tissues in the musculoskeletal system has been largely attributed to the glycosaminoglycan content. Recent work demonstrated anisotropy in the swelling response of the annulus fibrosus in the intervertebral disc. It is well known that collagen fiber orientation affects elastic behavior, but the effect of collagen fiber network on tissue swelling behavior is not well understood. In this study, we developed three series of models to evaluate the effect of collagen fiber orientation, fiber network architecture (i.e., single or multi-fiber families within a layer), and fiber stiffness on bulk tissue swelling, which was simulated by describing the extrafibrillar matrix as a triphasic material, as proposed by Lai et al. Model results were within one standard deviation of reported mean values for changes in tissue volume, width, and thickness under free swelling conditions. The predicted swelling response of single-fiber family structures was highly dependent on fiber orientation and the number of lamellae in the bulk tissue. Moreover, matrix swelling resulted in tissue to twist, which reduced fiber deformations, demonstrating a balance between fiber deformation and matrix swelling. Large changes in fiber stiffness (20 × increase) had a relatively small effect on tissue swelling (~ 2% decrease in swelling). In conclusion, fiber angle, fiber architecture (defined as single- versus multiple fiber families in a layer), and the number of layers in a single fiber family structure directly affected tissue swelling behavior, including fiber stretch, fiber reorientation, and tissue deformation. These findings support the need to develop computational models that closely mimic the native architecture in order to understand mechanisms of stress distributions and tissue failure.

Two new species of Odontostilbe historically hidden under O. microcephala (Characiformes: Cheirodontinae)

ABSTRACT Specimens historically identified as Odontostilbe microcephala from the upper rio Paraná and Andean piedmont tributaries of the río Paraguay are reviewed and split in three species. We found that the distribution of O. microcephala is restricted to the Andean slope of the río Paraguay basin. The species is distinguished from congeners with subterminal mouth by the elongate body, usually 10-12 gill rakers on upper branch and smaller horizontal orbital diameter (24.6-32.8 % HL, mean 28.7%). Specimens from upper rio Paraná constitute two new species, diagnosed from other Cheirodontinae by the presence of mesopterygoid teeth, grouped on median portion and forming a continuous row. The new species are distinguished from each other by having premaxillary teeth with five cusps vs. nine cusps and by the number of lamellae in left and right sides of central median raphe of olfactory rosette with 20-21 vs. 11-12.

Effects of light intensities after anthesis on the photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize (Zea mays L. )

We examined the changes of photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize in response to different light intensities in the field, with the summer maize hybrid Denghai 605 as experimental material. Two treatments of both shading (S) and increasing light (L) from flowering to physiological maturity stage were designed, with the ambient sunlight treatment as control (CK). Under shading treatment, poorly developed thylakoid structure, blurry lamellar structure, loose granum, large gap between slices and warping granum were the major characteristics in chloroplast. Meanwhile, photosynthetic rate (Pn), transpiration rate, stomatal conductance, chlorophyll content, and actual photo-chemical efficiency (ΦPSII) decreased, whereas the maximal photochemical efficiency and non-photochemical quenching increased, which resulted in decreases in grain yield under shading treatment. However, a better development was observed in chloroplasts for L treatment, with the number of grana and lamellae increased and lamellae arranged compactly. In addition, Pn and ΦPSII increased under L treatment, which increased grain yield. The chloroplast arrangement dispersed in mesophyll cells and chloroplast ultrastructure was destroyed after shading, and then chlorophyll synthesis per unit leaf area and photosynthetic capacity decreased. In contrast, the number of grana and lamellae increased and lamellae arranged compactly after increasing light, which are beneficial for corn yield.

Vincenzo Malacarne (1744-1816) and the First Description of the Human Cerebellum.

Vincenzo Malacarne, professor of medicine, surgery, and obstetrics in Turin, Pavia, and Padua, Italy, represented a perfect example of an eighteenth century "letterato", combining interests in humanities, sciences, and politics, embodying the ideal of an encyclopedic and universal culture. He made important contributions in anatomy and surgery, teratology, obstetrics, neurology, and history of medicine, adopting a interdisciplinary approach based on the correlation between anatomy, surgery, and clinics. He deserves a special place in the history of neurology because of the first complete description of the human cerebellum. He quantified the units of the cerebellar internal structures, the lamellae being numbered for a systematic description of the human cerebellum. He thought the mental faculties depended on their number, considering a relation between the number of cerebellar lamellae and the expression of intellectual faculties. In this way, he made first statistics on human faculties. He advanced the concept that the number of cerebellar folia was influenced by the environment, thus providing the first nature-nurture hypothesis made on the basis of observations, and the concept of neuroplasticity in the scientific literature. Finally, he also contributed to the emergence of a new science, namely electrophysiology, because he laid down experimental foundations of a project on the recording of brain electricity, comparing the structure of the human brain with Volta's galvanic pillar.

Dynamic Monte Carlo simulations of effects of nanoparticle on polymer crystallization in polymer solutions

The presence of different nanoparticles can result in different polymer crystallization behaviors. Dynamic Monte Carlo simulations were used to study the effects of filler dimension and size on polymer crystallization. One-dimensional nanoparticle has the strongest ability to induce polymer crystallization, and can induce the formation of crystals with uniform orientation. The system filled with two-dimensional nanoparticle has the stronger crystallizability than that filled with zero-dimensional nanoparticle. Two factors, i.e., surface area and segmental orientation in interfacial regions, contribute to the different crystallizability. Further simulations revealed that more surface area can result in more interfacial oriented segments. In addition, it was found that the decrease of the length of one-dimensional filler causes the decrease of polymer crystallization rate and number of crystal lamellae. The decrease of the length of one-dimensional filler also leads to the drop of the degree of segmental orientation in interfacial regions, and thus crystal orientation was disrupted. These findings indicate that polymer crystallization behaviors could be effectively controlled by the addition of different nanofillers.

A new species of Hemidactylus (Squamata: Gekkota: Gekkonidae) from Qara Dagh Mountains, Kurdistan Region, with a key to the genus in Iraq.

We describe a new species of gecko of the genus Hemidactylus from the oak woodlands of Zagros Forest Steppe of Qara Dagh Mountains, Sulaimani, northeastern Iraq, based on morphological and molecular characteristics. Hemidactylus kurdicus sp. nov. is distinguished from all other related Arid clade Hemidactylus species in the Middle East by having a single pair of postmental scales; it differs H. turcicus, H. robustus, H. ulii, H. sinaitus, H. shihraensis and H. yerburii based on the number of lamellae under the first and fourth toes of pes. Mitochondrial DNA including CytB and 12S identify a consistent divergence between H. kurdicus and H. persicus. An identification key to the genus Hemidactylus in Iraq is presented.

Humic acid of commercial origin causes changes in gill morphology of silver catfish Rhamdia quelen exposed to acidic water: Response of silver catfish gills to low pH and humic acid.

The effect of dissolved organic carbon (DOC) against the burden of low pH was assessed in silver catfish Rhamdia quelen through the gills. A commercial humic acid (HA) was used as the source of DOC at 0 (control), 10, 25, and 50mg/l. For each HA concentration, two pH levels were tested: 6.5 (control) and 5.5. After 40 days of exposure, the gills were removed and morphological variables were analyzed through light and scanning electronic microscopy. The low water pH caused a reduction in the length of filaments, number of lamellae, and gill respiratory surface area (GRSA) and an increase in chloride cells (CCs) number in the filament epithelium. When HA was added to the test water, GRSA increased and CCs proliferated in lamellae, suggesting ionic and respiratory disturbances. Scanning electronic microscopy revealed that CC morphometric variables, that is, apical area, fractional area, and density, were undisturbed by the pH reduction, but increased in the presence of HA. This study indicates that the commercial HA did not protect silver catfish against low pH stress. Instead, it caused changes that may affect vital processes such as ion regulation and ventilation and, consequently, reduce growth.

Gross brain morphology of the armoured catfish Rineloricaria heteroptera, Isbrücker and Nijssen (1976), (Siluriformes: Loricariidae: Loricariinae): A descriptive and quantitative approach.

The gross morphology of the brain of Rineloricaria heteroptera and its relation to the sensory/behavioural ecology of the species is described and discussed. The sexual and ontogenetic intraspecific variation in the whole brain length and mass, as well as within/between the eight different brain subdivisions volumes, is also examined and discussed. Negative allometry for the whole brain length/mass and relative growth of the telencephalon and optic tecta was observed. Positive allometry was observed for the relative growth of the olfactory bulbs and medulla oblongata. Univariate and multivariate statistical analyses did not reveal significant differences in the brain subdivision growth rates among sexes and/or developmental stages, except for the optic tectum and some portions of the medulla oblongata, with juveniles and males showing more developed optic tecta and medullary subdivisions, respectively. The growth rates for each brain subdivision were relatively constant, and the slopes of the growth equations were almost parallel, except for those of the olfactory bulbs and medulla oblongata subdivisions, suggesting some degree of tachyauxesis of subdivisions against the entire brain. The corpus cerebelli was the more voluminous brain subdivision in most specimens (principally adults), followed by the optic tectum (the more voluminous subdivision in juveniles), hypothalamus, and telencephalon, in that order. Differences in the number of lamellae and relative size of the olfactory organ were also detected among developmental stages, which were more numerous and larger in adults. Based on these results, it is possible to infer an ontogenetic shift in the habitat/resource use and behaviour of R. heteroptera. Vision, primarily routed through the optic tectum, could be fundamental in early stages, whereas in adults, olfaction and taste, primarily routed through the olfactory bulbs and medulla oblongata, play more important roles.

Pulsed laser annealing of carbon black

Laser heating was used to study the rates and trajectories of carbon black during the earliest stages of annealing. A commercial carbon black, Regal 250 (R250 Cabot Corporation) was heated with a Q-switched Nd:YAG laser and a continuous wave CO2 laser. Structural transformations were observed with transmission electron microscopy. Micrographs were processed with in-house codes for the purpose of extracting distributions of fringe length, tortuosity (curvature), and number of lamellae per stack. Time-temperature-histories with nanosecond temporal resolution and temperature reproducibility within tens of degrees Celsius were determined by spectrally resolving the laser induced incandescence signal and applying multi-wavelength pyrometry. The Nd:YAG laser fluences include: 25, 50, 100, 200, 300, and 550 mJ/cm2. The maximum observed temperature ranged from 2400 °C to the C2 sublimation temperature of 4180 °C. The CO2 laser was used to collect a series of isothermal (2600 °C) heat treatments versus time (100 ms–20 s). Laser heated samples are compared against R250 annealed in a furnace at 2600 °C. The material transformation trajectory of Nd:YAG laser heated R250 was different than the traditional furnace heating. The traditional furnace annealing pathway is followed for CO2 laser heating as based upon equivalent end structures.

Ultraestructural analysis of human pre‐Descemet's tissue

PurposeTo analyze the elastic component of the posterior corneal stromal using electron transmission microscopy and inmunohistochemical techniques.MethodsFour pieces of cornea and sclero‐corneal angle were included in the study which were obtained from three deceased donors. The mean age was 57,67 years. From each piece a sample of tissue was processed for transmission electron microscopy examination and another sample was paraffin‐embedded for their study using optic microscopy. The optical sections were immunostained with anti‐fibrillin1 antibody.ResultsThe ultrastructural study showed that the posterior corneal stroma was comprised of fibrillary collagen lamellae.The number of lamellae vary from 3 to 10 in a random distribution from the line formed by the last queratocytes to the Descemet′s membrane. Mainly, the lamellae were separated by type IV collagen and elastic tissue. There were no differences between fibrillary collagen lamellas of the stroma anterior and posterior to the last line of queratocytes.In all cases, an electrodense band was observed alongside being closely related to the Descemet's membrane. This band was interrupted with gaps between the interruptions that vary in size and shape, like stitching. This band was continued towards the trabecular meshwork, where this material was located principally inside the trabecular sheets. This material appeared to be elastic tissue, this was confirmed by inmunostaining with anti‐ Fibrillin 1 antibody.ConclusionsPosterior stroma does not constitute a special layer of the cornea. However, a band of elastic tissue is observed close to the Descemet membrane that is continued into the trabecular meshwork. This elastic band could contribute notably to corneal biomechanical properties.

Genetic and morphological variability among the populations assigned to the genus Tropiocolotes Peters, 1880 (Squamata: Gekkonidae) in south Iran

Geckos of the genus Tropiocolotes are known from Africa through the Middle East to Iran and currently include ten recognized species. Recently Tropiocolotes naybandensis was described from Iran based on morphological data. Here, we confirm the taxonomic status of this species using both molecular and morphological data, and compare it with other populations of Tropiocolotes from Iran. A distinct new clade with high node support from southern Iran shows high genetic divergence from the clade of T. naybandensis and T. steudneri from Africa. Based on morphological examinations, three meristic characters differentiate the two clades: (1) number of gulars; (2) number of subdigital lamellae under first toe; (3) number of postmental scales. Data from two mtDNA genes (16S rRNA and COI) indicate mean genetic divergences for 16S and COI between T. naybandensis and a population from Bandar-e Lengeh of 3.8% and 6.2%, respectively. In addition, the genetic divergences between these two groups and a sample of T. steudneri from Egypt are 10.8% and 10.1% for 16S and 18% and 16.7% for COI, respectively. We thus confirm the specific status of T. naybandensis and present evidence for the existence of a new species level taxon of Tropiocolotes in south Iran.

Investigation of certain physical\u2013chemical features of oil recovery by an optimized alkali\u2013surfactant\u2013foam (ASF) system

The objective of this study is to discover a synergistic effect between foam stability in bulk and micro-emulsion phase behaviour to design a high-performance chemical system for an optimized alkaline–surfactant–foam (ASF) flooding for enhanced oil recovery (EOR). The focus is on the interaction of ASF chemical agents with oil in the presence and absence of a naphthenic acid component and in situ soap generation under bulk conditions. To do so, the impact of alkalinity, salinity, interfacial tension (IFT) reduction and in situ soap generation was systematically studied by a comprehensive measurement of (1) micro-emulsion phase behaviour using a glass tube test method, (2) interfacial tension and (3) foam stability analysis. The presented alkali–surfactant (AS) formulation in this study lowered IFT between the oil and aqueous phases from nearly 30 to 10−1–10−3 mN/m. This allows the chemical formulation to create considerably low IFT foam flooding with a higher capillary number than conventional foam for displacing trapped oil from porous media. Bulk foam stability tests demonstrated that the stability of foam diminishes in the presence of oil with large volumes of in situ soap generation. At lower surface tensions (i.e. larger in situ soap generation), the capillary suction at the plateau border is smaller, thus uneven thinning and instabilities of the film might happen, which will cause acceleration of film drainage and lamellae rupture. This observation could also be interpreted by the rapid spreading of oil droplets that have a low surface tension over the lamella. The spreading oil, by augmenting the curvature radius of the bubbles, decreases the surface elasticity and surface viscosity. Furthermore, the results obtained for foam stability in presence of oil were interpreted in terms of phenomenological theories of entering/spreading/bridging coefficients and lamella number.

Effect of Surface Dilatational Modulus on Foam Flow in a Porous Medium

Abstract In order to clarify the role of surface dilatational property in foam flow in a porous medium, three systems were prepared: a system with low surface dilatational modulus and high surface tension, a system with low surface dilatational modulus and low surface tension, and a system with high surface dilatational modulus and low surface tension. By measuring the lamella number and pressure drop across the porous medium, it has been found that differing from flow in a capillary tube, a system with high surface dilatational modulus could achieve a high pressure drop in a porous medium. The conclusion drawn as to the reason is that bubbles with smaller diameter resulting from a structure induced breakup and high dilatational modulus are the main reasons. Flow experiments at 40°C also demonstrate the effect of surface dilatational modulus on the pressure drop.

Clarification of the Terminology of the Olfactory Lamellae in Chondrichthyes.

Several papers regard the anatomy of the peripheral olfactory organ, the olfactory rosette, in the class of Chondrichtyes. The complex shape of this organ and the differences among species give clues to functional, evolutionary, and ecological observations; data on a larger number of species are needed in order to have a more complete insight. The rosette is made up of a central support and of numerous lamellae, which are lined by the sensory epithelium. The size, shape and number of these lamellae, which are highly variable among species, are noteworthy because they affect the sensory surface area, the water dynamic within the olfactory chamber, and the organization of the olfactory bulb. In the literature about Chondrichthyes, the definition of olfactory lamella is confused, because authors use the same words for different structures. The average number of lamellae is distinctive for each species, and the meaning of this difference is not completely understood and, in this frame, a not unambiguous definition of lamella leads to difficulties in comparing data from different publications and analyzing them together. We aim to give here an unambiguous definition of olfactory lamella, that should be each single fold of tissue extending from the raphe, and of lamellar number of a given species, that should be the average number of lamellae in one olfactory organ. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:2039-2045, 2017. © 2017 Wiley Periodicals, Inc.

Computational Parametric Analysis of the Mechanical Response of Structurally Varying Pacinian Corpuscles

The Pacinian corpuscle (PC) is a cutaneous mechanoreceptor that senses low-amplitude, high-frequency vibrations. The PC contains a nerve fiber surrounded by alternating layers of solid lamellae and interlamellar fluid, and this structure is hypothesized to contribute to the PC's role as a band-pass filter for vibrations. In this study, we sought to evaluate the relationship between the PC's material and geometric parameters and its response to vibration. We used a spherical finite element mechanical model based on shell theory and lubrication theory to model the PC's outer core. Specifically, we analyzed the effect of the following structural properties on the PC's frequency sensitivity: lamellar modulus (E), lamellar thickness (h), fluid viscosity (μ), PC outer radius (Ro), and number of lamellae (N). The frequency of peak strain amplification (henceforth "peak frequency") and frequency range over which strain amplification occurred (henceforth "bandwidth") increased with lamellar modulus or lamellar thickness and decreased with an increase in fluid viscosity or radius. All five structural parameters were combined into expressions for the relationship between the parameters and peak frequency, ωpeak=1.605×10-6N3.475(Eh/μRo), or bandwidth, B=1.747×10-6N3.951(Eh/μRo). Although further work is needed to understand how mechanical variability contributes to functional variability in PCs and how factors such as PC eccentricity also affect PC behavior, this study provides two simple expressions that can be used to predict the impact of structural or material changes with aging or disease on the frequency response of the PC.

Enhanced Screening for Ectasia Risk prior to Laser Vision Correction

ABSTRACT Aim To prospectively review current understanding and future trends of screening for keratectasia risk prior refractive laser vision correction (LVC). Background Progressive keratectasia is an uncommon but severe complication of LVC. Preoperative ectatic corneal disease is the most important risk factor. Screening for subclinical ectasia relies on proper interpretation of advanced diagnostic technologies, including front surface corneal topography, three-dimensional tomography, and biomechanical assessments. Summary Studies involving eyes with normal and stable corneas, compared to eyes with frank ectatic diseases and to eyes with normal topography from patients with very asymmetric ectasia, allow for developing advanced methods and testing its sensitivity. However, the ideal study populations for testing the sensitivity and specificity of ectasia risk assessments are respectively the preoperative of cases that developed ectasia and the ones with stable outcomes after LVC. Young age and low thickness are surrogates of corneal biomechanics, which may be replaced as risk factors by direct measurements. Keratectasia may also occur due to the surgical impact on corneal structure or due to significant trauma postoperatively. Percentage tissue altered higher than 40% is a more sensitive para­meter than a fixed value for minimal residual stromal bed of 250 µm. However, the biomechanical impact from surgery is related to the region and number of lamellae that are severed, so that flap thickness and geometry should play a more relevant role, which is in agreement with finite element simulations. Arti­ficial intelligence methods allow for combining parameters, which significantly enhance the accuracy for detecting ectasia risk. Conclusion An enhanced screening approach for preventing keratectasia should consider both preoperative patient-related data and procedure-related parameters to individually characterize ectasia susceptibility or predisposition. Clinical Significance Keratectasia is an uncommon, however, severe complication of LVC. Although prevention is the best strategy, an individualized enhanced ectasia screening approach for ectasia risk assessment prior to LVC procedures should integrate patient-related (individual ectasia susceptibility) and procedure-related parameters (biomechanical impact). How to cite this article Ambrósio Jr R, Belin MW. Enhanced Screening for Ectasia Risk prior to Laser Vision Correction. Int J Kerat Ect Cor Dis 2017;6(1):23-33.

Loss of Smooth Muscle α-Actin Leads to NF-κB-Dependent Increased Sensitivity to Angiotensin II in Smooth Muscle Cells and Aortic Enlargement.

Mutations in ACTA2, encoding the smooth muscle isoform of α-actin, cause thoracic aortic aneurysms, acute aortic dissections, and occlusive vascular diseases. We sought to identify the mechanism by which loss of smooth muscle α-actin causes aortic disease. Acta2-/- mice have an increased number of elastic lamellae in the ascending aorta and progressive aortic root dilation as assessed by echocardiography that can be attenuated by treatment with losartan, an angiotensin II (AngII) type 1 receptor blocker. AngII levels are not increased in Acta2-/- aortas or kidneys. Aortic tissue and explanted smooth muscle cells from Acta2-/- aortas show increased production of reactive oxygen species and increased basal nuclear factor κB signaling, leading to an increase in the expression of the AngII receptor type I a and activation of signaling at 100-fold lower levels of AngII in the mutant compared with wild-type cells. Furthermore, disruption of smooth muscle α-actin filaments in wild-type smooth muscle cells by various mechanisms activates nuclear factor κB signaling and increases expression of AngII receptor type I a. These findings reveal that disruption of smooth muscle α-actin filaments in smooth muscle cells increases reactive oxygen species levels, activates nuclear factor κB signaling, and increases AngII receptor type I a expression, thus potentiating AngII signaling in vascular smooth muscle cells without an increase in the exogenous levels of AngII.

Effect of water-nitrogen coupling on photosynthesis and ultrastructure of cucumber leaves under CO2 enrichment

Using split plot and then-split plot design, effects of water-nitrogen coupling on photosynthesis and ultrastructure of cucumber (Cucumis sativus) (Jinyou No.35) under CO2 enrichment were investigated. The main plot had two CO2 concentrations: ambient CO2 concentration (400 μmol·mol-1, A) and doubled CO2 concentration (800±20 μmol·mol-1, E). The split plot had two treatments: no drought stress (95% of field capacity, W) and drought stress (75% of field capacity, D). The then-split plot contained low nitrogen treatment (450 kg·hm-2, N1) and high nitrogen treatment (900 kg·hm-2, N2). The results showed that under the condition of drought and high nitrogen, increasing CO2 enhanced the cucumber plant height, and no matter what kinds of water treatment, CO2 enrichment increased the leaf area significantly under high nitrogen. Under the condition of normal irrigation, the photosynthetic rate, stomatal conductance and transpiration rate of high nitrogen treatment were higher than low nitrogen treatment, while it was under the drought condition. Elevated CO2 enhanced the water use efficiency of cucumber leaf which increased with increasing nitrogen application rate. Under drought stress, cucumber adaxial surface porosity density was increased, and the CO2 enrichment and high nitrogen significantly reduced the stomatal density. Increasing nitrogen application improved the number of chloroplast, and reduced that of starch grains. Drought stress decreased the number of chloroplast, but tended to promote the number of starch grains. Drought stress increased the chloroplast length and width, and the size of the starch grains, while high nitrogen reduced the length and width of the chloroplast and starch grains. CO2 enrichment and high nitrogen increased grana thickness and layers (except ADN2), and the slice layer of EDN2 was significantly higher than that of ADN2. In conclusion, CO2 enrichment and suitable water and nitrogen could promote the development of chloroplast thylakoid membrane system, significantly increase the thickness of grana and the number of grana lamella, and effectively improve the chloroplast structure of cucumber, which would benefit the photosynthesis of cucumber plants and ability to utilize CO2 and water and nitrogen.

Incorporation of interfacial roughness into recursion matrix formalism of dynamical X-ray diffraction in multilayers and superlattices.

Diffraction in multilayers in the presence of interfacial roughness is studied theoretically, the roughness being considered as a transition layer. Exact (within the framework of the two-beam dynamical diffraction theory) differential equations for field amplitudes in a crystalline structure with varying properties along its surface normal are obtained. An iterative scheme for approximate solution of the equations is developed. The presented approach to interfacial roughness is incorporated into the recursion matrix formalism in a way that obviates possible numerical problems. Fitting of the experimental rocking curve is performed in order to test the possibility of reconstructing the roughness value from a diffraction scan. The developed algorithm works substantially faster than the traditional approach to dealing with a transition layer (dividing it into a finite number of thin lamellae). Calculations by the proposed approach are only two to three times longer than calculations for corresponding structures with ideally sharp interfaces.

Reconciling phylogenetic and morphological trends in North American Mammuthus

The morphology of mammoth upper third permanent molars (M3) is used to address regional- and continental-scale patterns in the structure of mammoth populations. Recent refinements to the understanding of Mammuthus phylogenetic diversity south of the Laurentide ice show extensive overlap between regional populations. We assess the underlying geographic structure in Mammuthus tooth morphology in light of these new genetic data. Comparison of regional trends in dental morphology show a single, morphologically variable, population of Mammuthus was present in North America during the Wisconsin glaciation. Within this population, there are no significant differences in degree of hypsodonty or molar shape however, there is a geographic pattern of lower enamel:dentin ratios in Mammuthus from the Channel Islands, West Coast, and Southwest/Mexico as measured by the number of molar lamellae and the standardized thickness of lamellae. These results contrast with historical perspectives of Mammuthus population structure suggesting at least four species of North American mammoths but are consistent with recent phylogeographic analyses of mitochondrial ancient DNA.