The shape and erosion of pebbles

The shapes of flat pebbles may be characterized in terms of the statistical distribution of curvatures measured along their contours. We illustrate this new method for clay pebbles eroded in a controlled laboratory apparatus, and also for naturally-occurring rip-up clasts formed and eroded in the Mont St.-Michel bay. We find that the curvature distribution allows finer discrimination than traditional measures of aspect ratios. Furthermore, it connects to the microscopic action of erosion processes that are typically faster at protruding regions of high curvature. We discuss in detail how the curvature may be reliable deduced from digital photographs.Comment: 10 pages, 11 figure

What is in a pebble shape?

We propose to characterize the shapes of flat pebbles in terms of the statistical distribution of curvatures measured along the pebble contour. This is demonstrated for the erosion of clay pebbles in a controlled laboratory apparatus. Photographs at various stages of erosion are analyzed, and compared with two models. We find that the curvature distribution complements the usual measurement of aspect ratio, and connects naturally to erosion processes that are typically faster at protruding regions of high curvature.Comment: Phys. Rev. Lett. (to appear

A multi-proxy approach to exploring Homo sapiens’ arrival, environments and adaptations in Southeast Asia

The capability of Pleistocene hominins to successfully adapt to different types of tropical forested environments has long been debated. In order to investigate environmental changes in Southeast Asia during a critical period for the turnover of hominin species, we analysed palaeoenvironmental proxies from five late Middle to Late Pleistocene faunas. Human teeth discoveries have been reported at Duoi U’Oi, Vietnam (70–60 ka) and Nam Lot, Laos (86–72 ka). However, the use of palaeoproteomics allowed us to discard the latter, and, to date, no human remains older than ~ 70 ka are documented in the area. Our findings indicate that tropical rainforests were highly sensitive to climatic changes over that period, with significant fluctuations of the canopy forests. Locally, large-bodied faunas were resilient to these fluctuations until the cooling period of the Marine Isotope Stage 4 (MIS 4; 74–59 ka) that transformed the overall biotope. Then, under strong selective pressures, populations with new phenotypic characteristics emerged while some other species disappeared. We argue that this climate-driven shift offered new foraging opportunities for hominins in a novel rainforest environment and was most likely a key factor in the settlement and dispersal of our species during MIS 4 in SE Asia

Agonist-Directed Desensitization of the β2-Adrenergic Receptor

The β2-adrenergic receptor (β2AR) agonists with reduced tachyphylaxis may offer new therapeutic agents with improved tolerance profile. However, receptor desensitization assays are often inferred at the single signaling molecule level, thus ligand-directed desensitization is poorly understood. Here we report a label-free biosensor whole cell assay with microfluidics to determine ligand-directed desensitization of the β2AR. Together with mechanistic deconvolution using small molecule inhibitors, the receptor desensitization and resensitization patterns under the short-term agonist exposure manifested the long-acting agonism of salmeterol, and differentiated the mechanisms of agonist-directed desensitization between a full agonist epinephrine and a partial agonist pindolol. This study reveals the cellular mechanisms of agonist-selective β2AR desensitization at the whole cell level

Fossil Carder Bee's nest from the Hominin locality of Taung, South Africa

The Buxton-Norlim Limeworks southwest of Taung, South Africa, is renowned for the discovery of the first Australopithecus africanus fossil, the ‘Taung Child’. The hominin was recovered from a distinctive pink calcrete that contains an abundance of invertebrate ichnofauna belonging to the Coprinisphaera ichnofacies. Here we describe the first fossil bee’s nest, attributed to the ichnogenus Celliforma, from the Plio-Pleistocene of Africa. Petrographic examination of a cell lining revealed the preservation of an intricate organic matrix lined with the calcitic casts of numerous plant trichomes–a nesting behaviour unique to the modern-day carder bees (Anthidiini). The presence of Celliforma considered alongside several other recorded ichnofossils can be indicative of a dry, savannah environment, in agreement with recent work on the palaeoenvironment of Plio-Pleistocene southern Africa. Moreover, the occurrence of ground-nesting bees provides further evidence that the pink calcrete deposits are of pedogenic origin, rather than speleogenic origin as has previously been assumed. This study demonstrates the potential value of insect trace fossils as palaeoenvironmental indicators

HAMLET Binding to α-Actinin Facilitates Tumor Cell Detachment

Cell adhesion is tightly regulated by specific molecular interactions and detachment from the extracellular matrix modifies proliferation and survival. HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells) is a protein-lipid complex with tumoricidal activity that also triggers tumor cell detachment in vitro and in vivo, suggesting that molecular interactions defining detachment are perturbed in cancer cells. To identify such interactions, cell membrane extracts were used in Far-western blots and HAMLET was shown to bind α-actinins; major F-actin cross-linking proteins and focal adhesion constituents. Synthetic peptide mapping revealed that HAMLET binds to the N-terminal actin-binding domain as well as the integrin-binding domain of α-actinin-4. By co-immunoprecipitation of extracts from HAMLET-treated cancer cells, an interaction with α-actinin-1 and -4 was observed. Inhibition of α-actinin-1 and α-actinin-4 expression by siRNA transfection increased detachment, while α-actinin-4-GFP over-expression significantly delayed rounding up and detachment of tumor cells in response to HAMLET. In response to HAMLET, adherent tumor cells rounded up and detached, suggesting a loss of the actin cytoskeletal organization. These changes were accompanied by a reduction in β1 integrin staining and a decrease in FAK and ERK1/2 phosphorylation, consistent with a disruption of integrin-dependent cell adhesion signaling. Detachment per se did not increase cell death during the 22 hour experimental period, regardless of α-actinin-4 and α-actinin-1 expression levels but adherent cells with low α-actinin levels showed increased death in response to HAMLET. The results suggest that the interaction between HAMLET and α-actinins promotes tumor cell detachment. As α-actinins also associate with signaling molecules, cytoplasmic domains of transmembrane receptors and ion channels, additional α-actinin-dependent mechanisms are discussed

An unprecedented condensation pathway leading to the formation of phenolic C40 bis-diterpenoids in sediments from the Lower Oligocene of the Rhine Rift Valley.

International audienc

Composition and antibacterial activity of essential oils obtained from plants of the Lamiaceae family against pathogenic and beneficial bacteria

The qualitative composition and antibacterial activity of six essential oils obtained from plants cultivated in the Colombian Andes (Mentha spicata, Mentha piperita, Ocimum basilicum, Salvia officinalis, Rosmarinus officinalis and Thymus vulgaris) and a commercial essential oil of Origanum vulgare subsp. hirtum were investigated. The essential oil composition was determined by gas chromatography-mass spectrometry (GC-MS), while the antibacterial activity of the essential oils against Escherichia coli, Salmonella enteritidis, Salmonella typhimurium, Lactobacillus acidophilus and Bifidobacterium breve was measured as the minimum bacte icidal concentration (MBC) using the agar dilution method. The chemical analysis revealed the presence of 16-28 compounds in each oil, corresponding mainly to phenols, oxygenated and hydrocarbon monoterpenes. O. vulgare and T. vulgaris oils were active at low MBCs (MBC . 5 mg/ml) against all bacteria evaluated, including beneficial microorganisms. In contrast, O. basilicum oil was more active against pathogenic bacteria (MBCs . 10mg/ml) than beneficial bacteria (MBCs of 80 mg/ml). The present study shows that the antimicrobial potential of essential oils depends not only on the chemical composition of the oil but also on the targeted microorganism. This has important practical implications for essential oils intended to be used as feed additives with antibacterial properties for animal nutrition or pharmaceutical products with natural compounds.Pesquisou-se a composicao qualitativo e a atividade antibacteriana de seis azeites essenciais obtidos de plantas cultivadas nos Andes Colombianos (Mentha spicata, Mentha piperita, Ocimum basilicum, Salvia officinalis, Rosmarinus officinalis e Thymus vulgaris) e um azeite essencial comercial de Origanum vulgare subsp. hirtum. A composicao dos azeites essenciais foi determinada por cromatografia de gases - espectrofotometria de massas (CM-EM), enquanto a atividade antibacteriana dos azeites essenciais contra Escherichia coli, Salmonella enteritidis, Salmonella typhimurim, Lactobacillus acidophilus e Bifidobacterium breve foi medida como a concentracao minima bactericida (CMB) usando o metodo de diluicao em agar. As analises quimicas revelaram a presenca de16 . 28 compostos em cada azeite, correspondendo principalmente a monoterpenos fenolicos, hidrocarbonetos e oxigenados. Os azeites de O. vulgare e T. vulgaris foram ativos contra todas as bacterias testadas, incluindo microorganismos beneficos a CMBs baixas (CMB . 5 mg/ml). Em contraste, o azeite de O. basilicum foi mais ativo contra bacterias patogenicas do que bacterias beneficas (CMBs de 80 mg/ml). Este estudo demonstrou o potencial antimicrobiano dos azeites essenciais depende da composicao quimica do azeite e o microorganismo proprio. Estes resultados tem implicacoes praticas para os azeites essenciais usados como aditivos alimenticios com propriedades antibacterianas para a nutricao animal ou produtos farmaceuticos com produtos naturais.Se investigo la composicion cualitativa y la actividad antibacteriana de seis aceites esenciales obtenidos de plantas cultivadas en los Andes Colombianos (Mentha spicata, Mentha piperita, Ocimum basilicum, Salvia officinalis, Rosmarinus officinalis y Thymus vulgaris) y un aceite esencial comercial de Origanum vulgare subsp. hirtum. La composicion de los aceites esenciales fue determinada por cromatografia de gases- espectrofotometria de masas (CG-EM), mientras que la actividad antibacteriana de los aceites esenciales contra Escherichia coli, Salmonella enteritidis, Salmonella typhimurim, Lactobacillus acidophilus y Bifidobacterium breve, fue medida como la concentracion minima bactericida (CMB) usando el metodo de dilucion en agar. Los analisis quimicos revelaron la presencia de16 . 28 compuestos en cada aceite, correspondiendo principalmente a monoterpenos fenolicos, oxigenados e hidrocarbonos. Los aceites de O. vulgare y T. vulgaris fueron activos contra todas las bacterias evaluadas, incluyendo microorganismos beneficos a CMBs bajas (CMB . 5 mg/ml). En contraste, el aceite de O. basilicum fue mas activo contra bacterias patogenas (CMBs . 10 mg/ml) en comparacion de bacterias beneficas (CMBs de 80 mg/ml). El presente estudio demostro que el potencial antimicrobiano de los aceites esenciales no depende solo de la composicion quimica del aceite sino tambien del microorganismo por si mismo. Estos resultados tienen implicaciones practicas para los aceites esenciales usados como aditivos alimenticios con propiedades antibacterianas para la nutricion animal o productos farmaceuticos con compuestos naturales