Facet Orientation Research Articles

The biomechanical impact of facet tropism on the intervertebral disc and facet joints in the cervical spine

Background ContextFacet tropism is defined as the angular difference between the left and the right facet orientation. Facet tropism was suggested to be associated with the disc degeneration and facet degeneration in the lumbar spine. However, little is known about the relationship between facet tropism and pathologic changes in the cervical spine and the mechanism behind. PurposeThis study was conducted to investigate the biomechanical impact of facet tropism on the intervertebral disc and facet joints. Study DesignA finite element analysis study. MethodsThe computed tomography (CT) scans of a 28-year-old male volunteer was used to construct the finite element model. First, a symmetrical cervical model from C2 to C7 was constructed. The facet orientations at each level were simulated using the data from our previously published study. Second, the facet orientations at the C5–C6 level were altered to simulate facet tropism with respect to the sagittal plane. The angular difference of the moderate facet tropism model was set to be 7 degrees, whereas the severe facet tropism model was set to be 14 degrees. The inferior of the C7 vertebra was fixed. A 75 N follower loading was applied to simulate the weight of the head. A 1.0 N⋅m moments was applied on the odontoid process of the C2 to simulate flexion, extension, lateral bending, and axial rotation. ResultsThe intradiscal pressure (IDP) at the C5–C6 level of the severe facet tropism model increased by 49.02%, 57.14%, 39.06%, and 30.67%, under flexion, extension, lateral bending, and axial rotation moments, in comparison with the symmetrical model. The contact force of the severe facet tropism model increased by 35.64%, 31.74%, 79.26%, and 59.47% from the symmetrical model under flexion, extension, lateral bending, and axial rotation, respectively. ConclusionsFacet tropism with respect to the sagittal plane at the C5–C6 level increased the IDP and facet contact force under flexion, extension, lateral bending, and axial rotation. The results suggested that facet tropism might be the anatomic risk factor of the development of cervical disc degeneration or facet degeneration. Future clinical studies are in need to verify the biomechanical impact of facet tropism on the development of degenerative changes in the cervical spine.

Pine‐Leaf‐Shaped α‐Fe2O3 Micro/Nanostructures with a Preferred Orientation along the (110) Plane for Efficient Reversible Lithium Storage

AbstractPine‐leaf‐like α‐Fe2O3 micro/nanostructures with (110)‐facet orientations are prepared by a hydrothermal process using Mg2+ as an inducer and are investigated as conversion‐type anode materials for lithium‐ion batteries (LIBs). The unique micro/nanostructured building blocks significantly shorten the diffusion distance for lithium ions and improve the kinetics of the lithium ion extraction/insertion process, and the unique hierarchical morphology provide buffer space for the volume change of the electrode during the charge–discharge processes. Thus, favorable performances for lithium storage are demonstrated for the micro/nanostructured α‐Fe2O3 electrodes. In addition, the facet orientation of the particles is also found to have a substantial impact on the electrode performance, and the growth of the micro/nanoparticles in a preferred orientation along the (110) plane facilitated the anisotropic diffusion of lithium ions along channels in the [1 00] direction. From the dual benefits of the stable hierarchical micro/nanostructure and the preferred growth of the particles along the (110) plane, excellent electrochemical performance with a reversible capacity of up to 915 and 565 mA h g−1 at rates of 100 and 5000 mA g−1, respectively, and a capacity retention of 690 mA h g−1 at 1000 mA g−1 after 200 cycles is demonstrated for the α‐Fe2O3 micro/nanostructure prepared under optimized conditions.

An Electrochemically Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting

AbstractBiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed‐assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4, exhibiting a remarkable photocurrent density of 2.5 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10‐fold higher than that of the pristine photoanode. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm−2, delivering an applied bias photon‐to‐current efficiency (ABPE) of 1.1 %. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. These findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.

An Electrochemically Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting.

BiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed-assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4 , exhibiting a remarkable photocurrent density of 2.5 mA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10-fold higher than that of the pristine photoanode. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm-2 , delivering an applied bias photon-to-current efficiency (ABPE) of 1.1 %. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. These findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.

Multitude of PTCDA Superstructures on Ag(111) and Vicinal Surfaces

Organic molecules that covalently bond to metal surfaces, like perylene tetracarboxylic acid dianhydride (PTCDA) on Ag, may cause large-scale reconstruction of the interface, in particular if the adsorption takes place on a “stepped” (i.e., vicinal) surface. Under certain conditions, such surfaces develop a large variety of high-index facets that are stabilized by superstructures of the PTCDA adsorbate. These superstructures can be commensurate, point-on-line, or incommensurate with respect to the substrate facets depending on facet orientation and step direction. The present scanning tunneling microscopy and low-energy electron diffraction data were taken from two different vicinal surfaces, Ag(775) and Ag(10 8 7), both inclined by 8.5° with respect to the (111) direction but in different azimuthal directions. Altogether, we identify and evaluate 18 new superstructures and correlate their data with the properties of the corresponding facets. The observed richness of superstructures and the occurrence of ...

Catalysts Facet Orientation and Surface Modifications for Improved Activity of Alcohol Oxidation

Many problems encountered in hydrogen-fuel-cell technology, particularly those of hydrogen storage and distribution, can be circumvented by replacing hydrogen with liquid fuels, such as methanol and ethanol. However, the electrocatalytic oxidation reactions of methanol and ethanol are slow and incomplete even on the best existing Pt-based catalysts, which greatly impeded the wide-spread application of direct alcohol fuel cell (DAFC). Our group demonstrated that one class of surfaces can be very active for the oxidation of methanol and ethanol [1]. These electrocatalysts consist of one Pt monolayer (PtML) under tensile strain when placed on extended or nanoparticle surfaces. Their activity and selectivity can be controlled with Pt-support interaction. Our experimental and DFT studies demonstrated a correlation between the strain induced by PtML-support interaction and the catalytic activity. Significant enhancement in the activity associated with the tensile strain and decreased activity associated with the compressive strain. Most recently, we deposited PtML on Au single crystals and shape-controlled nanocrystals enclosed with different crystallographic facets[1,2], and electrochemical behaviors (Figure 1a) suggested that the deposited PtML possessed facets matching to the underlying Au. Surface structure can determine catalytic properties and a large density of atomic steps on high-index facets is especially desirable for breaking chemical bonds such as C-C bond splitting in ethanol total oxidation. Such property of translating facet-specific features from substrates to the supported PtMLopens new opportunities to enhance catalytic performances. Another approach to improve activity involves modifying PtML surfaces with different co-catalysts. For example, Ru modified PtML/Au showed significantly enhanced activity for methanol oxidation and FTIR studies demonstrated that no adsorbed CO was formed during the reaction. The incorporation of co-catalysts such as Rh, Ir and Sn with PtML shifted onset potential of ethanol oxidation to more negative values (Figure 1b) and promoted a complete oxidation of ethanol to CO2. Details of electrochemical, structural and spectroscopic studies, discussion of reaction mechanisms and possibilities of these findings to resolve the major impediment hindering the development of practical DAFCs and to open new studies of C-C bond splitting in variety of important reactions will be presented in the meeting. Acknowledgements This work was financially supported by the US DOE, Office of Basic Energy Science, Material Science and Engineering Division, Division of Chemical Sciences, Geosciences and Biosciences Division (Contract No. DE-SC0012704).

Functional analyses of the primate upper cervical vertebral column

Recent work has highlighted functional correlations between direct measures of head and neck posture and primate cervical bony morphology. Primates with more horizontal necks exhibit middle and lower cervical vertebral features that indicate increased mechanical advantage for deep nuchal musculature and mechanisms for column curvature formation and maintenance. How features of the C1 and C2 reflect quantified measures of posture have yet to be examined. This study incorporates bony morphology from the upper cervical levels from 20 extant primate species in order to investigate further how posture correlates with cervical vertebrae morphology. Results from phylogenetic generalized least-squares analyses indicate that few vertebral features exhibit a significant relationship with posture when accounting for differences in size. When size-adjusted traits were correlated with posture, vertebral variation had a stronger relationship with neck posture than head posture variables. Two C1 traits—relative posterior arch length and superior facet curvature—were correlated with neck posture variables. Relative posterior arch length exhibits a positive relationship with neck posture, while superior articular facet curvature demonstrates a negative relationship, such that as the neck becomes more horizontal, the greater the facet curvature. Four C2 features were also correlated with neck posture: relative pedicle and lamina lengths, relative superior facet orientation, and dens orientation. Relative pedicle and lamina lengths become craniocaudally longer as the neck becomes more horizontal. Relative C2 superior facet orientation and dens orientation exhibit negative correlations with posture, such that as the neck becomes more horizontal, the superior facet becomes more caudally inclined and the dens more dorsally inclined. These results produce a similar functional signal observed in the middle and lower cervical spine. Modeling the cervical vertebrae of more pronograde taxa within a sigmoidal spinal column model is further discussed and may prove useful in refining and testing future hypotheses of primate cervical mechanics.

Three-dimensional morphometric analysis of the talus: implication for variations in kinematics of the subtalar joint.

Three-dimensional (3D) movement of the clinical subtalar joint (CSTJ) is primarily determined by the morphology of the articular surfaces of the talus. The purposes of this study were to assess the 3D orientation of the CSTJ facets of the talus and the talar head and to determine the tri-axial angular relationship. Fifty dry tali were scanned using computed tomography to create a 3D bone model of the talus. The tri-axial angles of the anterior, middle, and posterior facets and the talar head were calculated. A correlation analysis between the angles of the posterior facet and the talar head was also performed. The transverse angle at both the posterior facet and the talar head was significantly correlated with the sagittal angle (r = -0.441, p < 0.001; and r = -0.694, p < 0.001, respectively). The sagittal angle of the posterior facet was significantly correlated with that of the talar head (r = 0.478, p < 0.001). When the posterior facet of the talus and the talar head exhibits a greater downward and lesser medial orientation, a greater inversion/eversion at the CSTJ should be induced, while an opposite orientation should induce greater plantarflexion/dorsiflexion and medial/lateral rotation at the CSTJ. Our findings will be useful for planning rehabilitation programs and surgical interventions to correct the subtalar joint orientation in clinical settings.

Hyperlordosis is Associated With Facet Joint Pathology at the Lower Lumbar Spine.

A retrospective study. Our study opted to clarify the remaining issues of lumbar lordosis (LL) with regard to (1) its physiological values, (2) age, (3) sex, and (4) facet joint (FJ) arthritis and orientation using computed tomography (CT) scans. Recent studies have questioned whether LL really decreases with age, but study sample sizes have been rather small and mostly been based on x-rays. As hyperlordosis increases the load transferred through the FJs, it seems plausible that hyperlordosis may lead to FJ arthritis at the lower lumbar spine. We retrospectively analyzed the CT scans of 620 individuals, with a mean age of 42.5 (range, 14-94) years, who presented to our traumatology department and underwent a whole-body CT scan, between 2008 and 2010. LL was evaluated between the superior endplates of L1 and S1. FJs of the lumbar spine were evaluated for arthritis and orientation between L2 and S1. (1) The mean LL was 49.0 degrees (SD 11.1 degrees; range, 11.4-80.1 degrees). (2) LL increased with age and there was a significant difference in LL in our age groups (30 y and below, 31-50, 51-70, and ≥71 y and above) (P=0.02). (3) There was no significant difference in LL between females and males (50 and 49 degrees) (P=0.17). (4) LL showed a significant linear association with FJ arthritis [P=0.0026, OR=1.022 (1.008-1.036)] and sagittal FJ orientation at L5/S1 (P=0.001). In a logistic regression analysis, the cutoff point for LL was 49.4 degrees. This is the largest CT-based study on LL and FJs. LL significantly increases with age. As a novelty finding, hyperlordosis is significantly associated with FJ arthritis and sagittal FJ orientation at the lower lumbar spine. Thus, hyperlordosis may present with back pain and patients may benefit from surgical correction, for example, in the setting of trauma.

The Neandertal vertebral column 2: The lumbar spine

Here we provide the most extensive metric and morphological analysis performed to date on the Neandertal lumbar spine. Neandertal lumbar vertebrae show differences from modern humans in both the vertebral body and in the neural arch, although not all Neandertal lumbar vertebrae differ from modern humans in the same way. Differences in the vertebral foramen are restricted to the lowermost lumbar vertebrae (L4 and L5), differences in the orientation of the upper articular facets appear in the uppermost lumbar vertebrae (probably in L1 and L2–L3), and differences in the horizontal angle of the transverse process appear in L2–L4. Neandertals, when compared to modern humans, show a smaller degree of lumbar lordosis. Based on a still limited fossil sample, early hominins (australopiths and Homo erectus) had a lumbar lordosis that was similar to but below the mean of modern humans. Here, we hypothesize that from this ancestral degree of lumbar lordosis, the Neandertal lineage decreased their lumbar lordosis and Homo sapiens slightly increased theirs. From a postural point of view, the lower degree of lordosis is related to a more vertical position of the sacrum, which is also positioned more ventrally with respect to the dorsal end of the pelvis. This results in a spino-pelvic alignment that, though different from modern humans, maintained an economic postural equilibrium. Some features, such as a lower degree of lumbar lordosis, were already present in the middle Pleistocene populations ancestral to Neandertals. However, these middle Pleistocene populations do not show the full suite of Neandertal lumbar morphologies, which probably means that the characteristic features of the Neandertal lumbar spine did not arise all at once.

The Facet Orientation of the Subaxial Cervical Spine and the Implications for Cervical Movements and Clinical Conditions.

Computed tomography study. To obtain detailed information on the facet orientation in the subaxial cervical spine and explore the correlation to the cervical movements and relevant clinical conditions. Although facet orientation was well studied in the lumbar spine, the literatures on the cervical facet orientation were limited and the descriptions were nonspecific. The computed tomography scans of 100 individuals were reconstructed. For each level from C2/C3 to C6/C7, the horizontal plane, the mid-sagittal plane, the coronal plane, and the two facet planes were established. The normal vectors of the five planes were used for the calculation of the facet orientation and the facet tropism. The angle of the facet plane with respect to the horizontal plane at the C6/7 level was the largest (left side: 64.34° ± 6.60°, right side: 63.37° ± 6.81°, P >0.05). The angle of the facet plane with respect to the coronal plane decreased from C2/C3 level to C6/C7 level. Regarding the angle of the facet plane with respect to the sagittal plane, for the paired facet joints, three types were found: posteromedially oriented, posterolaterally oriented, and ipsilaterally oriented. All (100%) of the facet joints at the C2/C3 level and 65% at the C3/C4 level were posteromedially oriented. In the lower levels of the cervical spine, the posteromedially oriented facet joints were less common. The facet tropism was common phenomenon in the subaxial cervical spine. This study provided detailed information on the facet orientation in the subaxial cervical spine. The cervical facet orientation correlated well with the spinal movements and related clinical conditions. 3.

Investigation of fatigue crack initiation facets in Ti-6Al-4V using focused ion beam milling and electron backscatter diffraction.

In the very high cycle fatigue regime, internal crack initiation can occur in Ti-6Al-4V because of the formation of facets, which are α grains that have fractured in a transcrystalline and planar manner. Because this crack initiation phase occupies most of the fatigue life, it is essential to understand which mechanisms lead to facet formation. Fatigue tests have been performed on drawn and heat-treated Ti-6Al-4V wires, and the facets at internal crack initiation sites have been analysed in detail in terms of their appearance, their spatial orientation and their crystallographic orientation. The facets were not smooth, but showed surface markings at the nanoscale. In nearly all cases, these markings followed a linear pattern. One anomalous facet, in a sample with the largest grain size, contained a fan-shaped pattern. The facets were at relatively steep angles, mostly between 50° and 70°. Cross-sections of the fracture surfaces have been made by focused ion beam milling and were used to measure the crystallographic orientation of facets by electron backscatter diffraction. Most facet planes coincided with a prismatic lattice plane, and the linear markings were parallel to the prismatic slip direction, which is a strong indication that prismatic slip and slip band formation led to crack initiation. However, the anomalous facet had a near-basal orientation, which points to a possible cleavage mechanism. The cross-sections also exposed secondary cracks, which had formed on prismatic lattice planes, and in some cases early stage facet formation and short crack growth phenomena. The latter observations show that facets can extend through more than one grain, and that there is crack coalescence between facets. The fact that drawn wires have a specific crystallographic texture has led to a different facet formation behaviour compared to what has been suggested in the literature.

Quantitative three‐dimensional ice roughness from scanning electron microscopy

AbstractWe present a method for inferring surface morphology of ice from scanning electron microscope images. We first develop a novel functional form for the backscattered electron intensity as a function of ice facet orientation; this form is parameterized using smooth ice facets of known orientation. Three‐dimensional representations of rough surfaces are retrieved at approximately micrometer resolution using Gauss‐Newton inversion within a Bayesian framework. Statistical analysis of the resulting data sets permits characterization of ice surface roughness with a much higher statistical confidence than previously possible. A survey of results in the range −39°C to −29°C shows that characteristics of the roughness (e.g., Weibull parameters) are sensitive not only to the degree of roughening but also to the symmetry of the roughening. These results suggest that roughening characteristics obtained by remote sensing and in situ measurements of atmospheric ice clouds can potentially provide more facet‐specific information than has previously been appreciated.

Facet-Dependent Thermal Instability in LiCoO2.

Thermal runaways triggered by the oxygen release from oxide cathode materials pose a major safety concern for widespread application of lithium ion batteries. Utilizing in situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at high temperatures, we show that oxygen release from LixCoO2 cathode crystals is occurring at the surface of particles. We correlated this local oxygen evolution from the LixCoO2 structure with local phase transitions spanning from layered to spinel and then to rock salt structure upon exposure to elevated temperatures. Ab initio molecular dynamics simulations (AIMD) results show that oxygen release is highly dependent on LixCoO2 facet orientation. While the [001] facets are stable at 300 °C, oxygen release is observed from the [012] and [104] facets, where under-coordinated oxygen atoms from the delithiated structures can combine and eventually evolve as O2. The novel understanding that emerges from the present study provides in-depth insights into the thermal runaway mechanism of Li-ion batteries and can assist the design and fabrication of cathode crystals with the most thermally stable facets.

Controlling Surface Termination and Facet Orientation in Cu2O Nanoparticles for High Photocatalytic Activity: A Combined Experimental and Density Functional Theory Study.

Cu2O nanoparticles with controllable facets are of great significance for photocatalysis. In this work, the surface termination and facet orientation of Cu2O nanoparticles are accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu2O nanoparticles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. Density functional theory simulations confirm that sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increase the density of exposed Cu atoms at the surfaces and thus benefit the photocatalytic activity. It also shows that the poor reactivity of the Cu-terminated Cu2O (100) surface is due to the high energy barrier of holes at the surface region.

Relationship between facet tropism and facet joint degeneration in the sub-axial cervical spine

BackgroundFacet tropism is the angular asymmetry between the left and right facet joint orientation. Although debatable, facet tropism was suggested to be associated with disc degeneration, facet degeneration and degenerative spondylolisthesis in the lumbar spine. The purpose of this study was to explore the relationship between facet tropism and facet degeneration in the sub-axial cervical spine.MethodsA total of 200 patients with cervical spondylosis were retrospectively analyzed. Facet degeneration was categorized into 4 grade: grade I, normal; grade II, degenerative changes including joint space narrowing, cyst formation, small osteophytes (<3 mm) without joint hypertrophy; grade III, joint hypertrophy secondary to large osteophytes (>3 mm) without fusion of the joint; grade IV, bony fusion of the facet joints. Facet orientations and facet tropisms with respect to the transverse, sagittal and coronal plane were calculated from the reconstructed cervical spine, which was based on the axial CT scan images. The paired facet joints were then categorized into three types: symmetric, moderated tropism and severe tropism. Univariate and multivariate analysis were performed to evaluate the relationship between any demographic and anatomical factor and facet degeneration.ResultsThe mean age of enrolled patients was 46.23 years old (ranging from 30 to 64 years old). There were 114 males and 86 females. The degrees of facet degeneration varied according to cervical levels and ages. Degenerated facet joints were most common at C2-C3 level and more common in patients above 50 years old. The facet orientations were also different from level to level. By univariate analysis, genders, ages, cervical levels, facet orientations and facet tropisms were all significantly different between the normal facets and degenerated facets. However, results from multivariate logistic regression suggested only age and facet tropism with respect to the sagittal plane were related to facet degeneration.ConclusionFacet degeneration were more common at C2-C3 level. Older age and facet tropism with respect to the sagittal plane were associated with the facet degeneration.

The role of allometry and posture in the evolution of the hominin subaxial cervical spine

Cervical vertebrae not only protect the spinal cord but also are the insertion and origin points for muscles related to the movement of the head, upper limb, and trunk, among others, and are thus important elements in primate evolution. While previous work has been undertaken on the first two cervical vertebrae, there is a dearth of studies on the subaxial cervical spine in hominines. In this paper, we provide detailed morphological information on two important aspects of the subaxial cervical vertebrae (C3 – C7): mid-sagittal morphology and superior facet orientation. We studied large samples of African apes including modern humans and the most complete fossil hominin subaxial cervical vertebrae using both traditional and geometric morphometrics. There are significant differences between extant hominoids related to the relative length and orientation of the spinous process as well as to the orientation of the articular facets, which are related to size, locomotion, and neck posture. In fact, fossil hominins do not completely conform to any of the extant groups. Our assessment of mid-sagittal morphology and superior articular facet orientation shows that australopiths have more Homo-like upper subaxial cervical vertebrae coupled with more “primitive” lower cervical vertebrae. Based on these results, we hypothesize that those changes, maybe related to postural changes derived from bipedalism, did not affect the entire subaxial cervical spine at once. From a methodological point of view, the combination of traditional and geometric morphometric data provides a more integrative perspective of morphological change and evolution, which is certainly useful in human evolutionary studies.

The cervical spine of Australopithecus sediba

Cervical vertebrae are rare in the early hominin fossil record, presenting a challenge for understanding the evolution of the neck and head carriage in hominin evolution. Here, we examine the cervical vertebrae of Australopithecus sediba, which unlike other South African taxa is known from associated cervical vertebrae. The A. sediba cervical vertebrae exhibit human-like values for wedging, pedicle cross-sectional areas, and articular facet heights, indicating reduced ventral loading relative to African apes. These features combine with a pattern of vertebral body bone distribution and caudally progressive size expansion suggesting a mode of cervical lordosis, load mitigation, and head carriage similar to humans and distinct from the cantilevered mode of head carriage of the extant African great apes. Yet these derived features in A. sediba are accompanied by ape-like vertebral body and dorsal pillar sizes, articular facet orientation, and uncinate process morphology signaling reduced lateral and rotational coupled movements between vertebral elements and indicate a considerably stiffer neck than in humans. A primitively long and horizontally-oriented C7 spinous process is likely related to a prognathic viscerocranium, although the complimentary C3 spinous process is short, implying large moments emanating from scapular and shoulder elevators rather than large muscles of head stabilization. Cross-sectional spinous process shape and robust anterior tubercles similarly signal increased arm elevation consistent with climbing behavior in corroboration with arboreal signatures previously observed in the shoulder, arms, and hand of A. sediba. Spinal canal shape and size suggests that A. sediba lacked the cervical spinal cord enlargement of Homo that confers humans with enhanced motor control to the upper limbs. The cervical spine of A. sediba thus presents a mosaic of primitive and derived characters, with anatomical features relating to neck posture and head carriage mirroring humans juxtaposed with most other aspects of functional anatomy that resemble chimpanzees.

Enhanced Activity of Ag Nanoplatelets on Few Layers of Graphene Film with Preferential Orientation for Dehydrogenative Silane–Alcohol Coupling

Ag nanoplatelets (4–7 nm height and 30–50 nm lateral size) supported on a few layers of graphene having preferential facet orientation have been prepared by pyrolysis of nanometric films of chitosan on quartz containing adsorbed Ag+ ions at 900 °C under argon. The strong interaction of Ag nanoplatelets and graphene has been deduced from the morphology of the Ag nanoplatelets, their dimensions, the preferential facet orientation, and the 0.4 eV shift toward higher values of the binding energy of the Ag 3d peak in XPS. The facet-oriented Ag on a few layers of graphene film exhibits for the dehydrogenative coupling of dimethylphenylsilane and n-butanol turnover numbers of 1.62 × 106 that are higher than that of analogous Ag-graphene catalysts lacking strong grafting and preferential orientation.

Sensing the facet orientation in silver nano-plates using scanning Kelvin probe microscopy in air

The work function of nano-materials is important for a full characterization of their electronic properties. Because the band alignment, band bending and electronic noise are very sensitive to work function fluctuations, the dependence of the work function of nano-scale crystals on facet orientation can be a critical issue in optimizing optoelectronic devices based on these materials. We used scanning Kelvin probe microscopy to assess the local work function on samples of silver nano-plates at sub-micrometric spatial resolution. With the appropriate choice of the substrate and based on statistical analysis, it was possible to distinguish the surface potential of the different facets of silver nano-plates even if the measurements were done in ambient conditions without the use of vacuum. A phenomenological model was used to calculate the differences of facet work function of the silver nano-plates and the corresponding shift in Fermi level. This theoretical prediction and the experimentally observed difference in surface potential on the silver nano-plates were in good agreement. Our results show the possibility to sense the nano-crystal facets by appropriate choice of the substrate in ambient conditions.