Recovery and Reconstruction of A.L. 444-2

2004 ◽  
Author(s):  
William H. Kimbel ◽  
Yoel Rak ◽  
Donald C. Johanson ◽  
Ralph L. Holloway ◽  
Michael S. Yuan
Keyword(s):  
Laser Fusion ◽  
Geological Age ◽  
Crystal Laser ◽  
Occlusal Wear ◽  
The Matrix ◽  
The Face ◽  
Temporal Bones ◽  
The Hill ◽  
Eastern Edge

The A.L. 444-2 skull was found on 26 February 1992, during a strategic paleontological survey of Kada Hadar Member sediments that are stratigraphically situated between BKT-1 and BKT-2 tephras, on the eastern edge of the Awash River’s Kada Hadar tributary. Yoel Rak discovered two fragments of hominin occipital bone (A.L. 444-1) at the base of a steep hill composed of Kada Hadar Member silts and clays capped by a weathered sandstone remnant. Subsequent examination of the upslope surface revealed additional hominin skull fragments (the temporal bones and maxillae) clustered together and partially exposed in a narrow gully that dissected the face of the hill. During the next seven days, probing and dry sieving of the gully infill and hillside colluvium over a 77 m2 area led to the recovery of fragments representing about 75%–80% of a single hominin skull. It was immediately apparent that the upslope finds duplicated the anatomical parts represented by the two A.L. 444-1 occipital fragments and therefore constituted a second hominin individual, cataloged as A.L. 444-2. In addition, the lambdoidal suture of the A.L. 444-1 occipital is completely unfused, suggesting subadult status, whereas fused cranial sutures and extreme dental occlusal wear indicate an advanced ontogenetic age for A.L. 444-2. In February–March 1993 the A.L. 444 hillside was excavated in an effort to locate missing parts of the A.L. 444-2 skull and to determine its precise stratigraphic provenance. No further remains of the hominin skull were encountered in situ, but a complete viverrid cranium and indeterminate fragments of large mammal bone with preservation and patina (mottled dark gray, white, and yellowish gray) identical to those of the hominin were excavated in an unstratified, cemented carbonate silt that exactly matches the matrix adhering to A.L. 444-2. We are confident that the hominin skull is from this sedimentary horizon. It is approximately 10.5 m stratigraphically below the BKT-2 tephra, which outcrops in the immediate vicinity of A.L. 444 Single-crystal laser fusion (SCLF) 40Ar/39Ar ages for BKT-2 and Kada Hadar Tuff (KHT) bracket the geological age of A.L. 444-2 between 2.94 and 3.18 Myr (Kimbel et al., 1994; Walter, 1994; Semaw et al., 1997).

scholarly journals Coexistence of Two Cubic-Lattice Co Matrices at High Temperatures in Co-Re-Cr-Ni Alloy Studied by Neutron Diffraction

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Přemysl Beran ◽  
Debashis Mukherji ◽  
Pavel Strunz ◽  
Ralph Gilles ◽  
Markus Hölzel ◽  
...  
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
Diffusion Processes ◽  
Phase Evolution ◽  
Ni Alloy ◽  
The Matrix ◽  
The Face ◽  
Fcc Phase ◽  
In Situ Neutron Diffraction

In situ neutron diffraction measurements were performed during heating to high temperature and cooling for a Co-17Re-23Cr-25Ni alloy. The allotropic transformation of the Co matrix and the evolution of the low-temperature hexagonal and high-temperature cubic Co phases were studied. A surprising observation was the splitting of the face-centred cubic (fcc) Co phase peaks at high temperature during heating as well as cooling. The phase evolution was monitored, and an appearance of the secondary fcc phase could be linked to the formation of σ phase (Cr2Re3 type) associated with a compositional change in the matrix due to diffusion processes at high temperature.

A re-evaluation of the Hart Ash, an important stratigraphic marker: Wright Valley, Antarctica

2019 ◽  
Vol 31 (3) ◽  
pp. 139-149
Author(s):  
M. Schiller ◽  
W.W. Dickinson ◽  
N.A. Iverson ◽  
J.A. Baker
Keyword(s):  
Trace Element ◽  
Laser Fusion ◽  
Soil Profiles ◽  
Dry Valleys ◽  
Volcanic Province ◽  
Crystal Laser ◽  
Tephra Layers ◽  
Surficial Deposits ◽  
Glass Shards

AbstractReliably dated surficial deposits for reconstructing palaeoclimate are rare in the McMurdo Dry Valleys of Antarctica. While many tephra have been found and dated, none is well characterized. In the Wright Valley, the Hart Ash is poorly dated and described. This paper reports profiles through tephra, the chemical signature of the glass shards and new high-precision multi-crystal laser fusion of 40Ar/39Ar ages. Major and trace element analyses of glass shards indicate the tephra are phonolitic and most probably sourced from Mount Discovery in the Erebus volcanic province. Two chemically distinct and stratigraphically separate tephra layers within the Hart Ash were found in three closely spaced soil profiles. The complex stratigraphy between these profiles could not be delineated without the geochemistry of the tephra. Importantly, our data suggest that only one tephra may be an in situ fall-out deposit, which gave a robust age of 2.97 ± 0.02 Ma. This new age for the Hart Ash tephra, which is 10 cm thick and is preserved at the current surface, provides a maximum age for surface deposits in the lower Wright Valley. This study highlights that well-characterized tephra enhance stratigraphic correlations in the Dry Valleys and improve the accuracy of palaeoenvironmental interpretations.

scholarly journals Supramolecular ionic polymer/carbon nanotube composite hydrogels with enhanced electromechanical performance

2020 ◽  
Vol 9 (1) ◽  
pp. 478-488 ◽  
Author(s):  
Yun-Fei Zhang ◽  
Fei-Peng Du ◽  
Ling Chen ◽  
Ka-Wai Yeung ◽  
Yuqing Dong ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Ion Mobility ◽  
Artificial Muscles ◽  
Ionic Polymer ◽  
Composite Hydrogels ◽  
The Matrix ◽  
Electromechanical Performance ◽  
Carbon Nanotube Composite ◽  
Robotic Devices

AbstractElectroactive hydrogels have received increasing attention due to the possibility of being used in biomimetics, such as for soft robotics and artificial muscles. However, the applications are hindered by the poor mechanical properties and slow response time. To address these issues, in this study, supramolecular ionic polymer–carbon nanotube (SIPC) composite hydrogels were fabricated via in situ free radical polymerization. The polymer matrix consisted of carbon nanotubes (CNTs), styrene sulfonic sodium (SSNa), β-cyclodextrin (β-CD)-grafted acrylamide, and ferrocene (Fc)-grafted acrylamide, with the incorporation of SSNa serving as the ionic source. On applying an external voltage, the ions accumulate on one side of the matrix, leading to localized swelling and bending of the structure. Therefore, a controllable and reversible actuation can be achieved by changing the applied voltage. The tensile strength of the SIPC was improved by over 300%, from 12 to 49 kPa, due to the reinforcement effect of the CNTs and the supramolecular host–guest interactions between the β-CD and Fc moieties. The inclusion of CNTs not only improved the tensile properties but also enhanced the ion mobility, which lead to a faster electromechanical response. The presented electro-responsive composite hydrogel shows a high potential for the development of robotic devices and soft smart components for sensing and actuating applications.

scholarly journals In situ structure and organization of the influenza C virus surface glycoprotein

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Steinar Halldorsson ◽  
Kasim Sader ◽  
Jack Turner ◽  
Lesley J. Calder ◽  
Peter B. Rosenthal
Keyword(s):  
Membrane Fusion ◽  
Hexagonal Lattice ◽  
Surface Glycoprotein ◽  
Structural Basis ◽  
Virus Surface ◽  
The Matrix ◽  
Influenza C Virus ◽  
Subtomogram Averaging ◽  
Electron Cryotomography

AbstractThe lipid-enveloped influenza C virus contains a single surface glycoprotein, the haemagglutinin-esterase-fusion (HEF) protein, that mediates receptor binding, receptor destruction, and membrane fusion at the low pH of the endosome. Here we apply electron cryotomography and subtomogram averaging to describe the structural basis for hexagonal lattice formation by HEF on the viral surface. The conformation of the glycoprotein in situ is distinct from the structure of the isolated trimeric ectodomain, showing that a splaying of the membrane distal domains is required to mediate contacts that form the lattice. The splaying of these domains is also coupled to changes in the structure of the stem region which is involved in membrane fusion, thereby linking HEF’s membrane fusion conformation with its assembly on the virus surface. The glycoprotein lattice can form independent of other virion components but we show a major role for the matrix layer in particle formation.

scholarly journals The Sorting of Mitochondrial DNA and Mitochondrial Proteins in Zygotes: Preferential Transmission of Mitochondrial DNA to the Medial Bud

1998 ◽  
Vol 142 (3) ◽  
pp. 613-623 ◽  
Author(s):  
Koji Okamoto ◽  
Philip S. Perlman ◽  
Ronald A. Butow
Keyword(s):  
Mitochondrial Dna ◽  
Fluorescent Protein ◽  
Yeast Cells ◽  
Mitochondrial Matrix ◽  
Outer Membranes ◽  
Marker Proteins ◽  
The Matrix ◽  
Green Fluorescent ◽  
Mitochondrial Reticulum

Green fluorescent protein (GFP) was used to tag proteins of the mitochondrial matrix, inner, and outer membranes to examine their sorting patterns relative to mtDNA in zygotes of synchronously mated yeast cells in ρ+ × ρ0 crosses. When transiently expressed in one of the haploid parents, each of the marker proteins distributes throughout the fused mitochondrial reticulum of the zygote before equilibration of mtDNA, although the membrane markers equilibrate slower than the matrix marker. A GFP-tagged form of Abf2p, a mtDNA binding protein required for faithful transmission of ρ+ mtDNA in vegetatively growing cells, colocalizes with mtDNA in situ. In zygotes of a ρ+ × ρ+ cross, in which there is little mixing of parental mtDNAs, Abf2p–GFP prelabeled in one parent rapidly equilibrates to most or all of the mtDNA, showing that the mtDNA compartment is accessible to exchange of proteins. In ρ+ × ρ0 crosses, mtDNA is preferentially transmitted to the medial diploid bud, whereas mitochondrial GFP marker proteins distribute throughout the zygote and the bud. In zygotes lacking Abf2p, mtDNA sorting is delayed and preferential sorting is reduced. These findings argue for the existence of a segregation apparatus that directs mtDNA to the emerging bud.

The contribution of friction stress to the creep behaviour of the nickel-base in situ composite, γ—γ'-Cr 3 C 2

1980 ◽  
Vol 373 (1752) ◽  
pp. 93-109 ◽  
Keyword(s):  
Activation Energy ◽  
Creep Behaviour ◽  
Friction Stress ◽  
Matrix Alloy ◽  
Dislocation Motion ◽  
Self Diffusion ◽  
The Matrix ◽  
Nickel Base ◽  
Distribution Of Stress

Transient creep following stress reductions has been analysed by the method described by McLean (1980) to determine the friction stress σ 0 as a function of temperature and directional solidification conditions for the γ-γ'-Cr 3 Cr 2 in-situ composite and for the γ-γ' matrix alloy. These values of σ 0 are identical to the flow stresses at creep strain rates and can be identified with the sums of the barriers to dislocation motion through the matrix by climb around γ'-particles and Orowan bowing between the carbide fibres. The friction stress and the kinetics of deformation of the composite are determined by the matrix behaviour, whereas its creep strength depends on the distribution of stress between fibre and matrix. When the steady-state creep behaviour of γ-γ'-Cr 3 C 2 is analysed by using the usual power law description in terms of the effective stress σ — σ 0 , rather than the applied stress σ, the stress exponent is ca 4 and the activation energy is similar to the activation energy of self-diffusion for nickel. The results provide strong evidence for the operation of recovery-creep in both the composite and matrix alloys.

Effect of pouring temperature on A356-TiB2 MMCs cast in sand and permanent moulds by in-situ method

2016 ◽  
Vol 25 (5-6) ◽  
pp. 165-169
Author(s):  
C. Rajaravi ◽  
P.R. Lakshminarayanan
Keyword(s):  
Evaluation Studies ◽  
Physical And Mechanical Properties ◽  
Xrd Analysis ◽  
Matrix Composites ◽  
Structure Property ◽  
Pouring Temperature ◽  
Matrix Metal ◽  
Property Evaluation ◽  
The Matrix

AbstractThe paper describes a different condition of pouring temperature by sand and permanent mould to produce A356-6 wt% TiB2 metal matrix composites by in-situ method salt metal reaction route. The observation of SEM micrographs shows particle distribution of the TiB2 and it appears in hexagonal shape in Al matrix. The results of X-ray diffraction (XRD) analysis confirmed the formation of those TiB2 particulates and the results showed TiB2 particles are homogeneously dispersed throughout the matrix metal. Subsequent structure-property evaluation studies indicated sub-micron size reinforcement of in-situ formed TiB2 particles with improved physical and mechanical properties as compared to sand and permanent mould of Al-TiB2 composites. From, the permanent mould Al-TiB2 composite has an advantage of increase the properties over sand mould Al-TiB2 composite.

Synthesize Ti3SiC2 and Ti3SiC2-Diamond Composites at High Pressure and High Temperature

2012 ◽  
Vol 512-515 ◽  
pp. 671-675 ◽  
Author(s):  
Ai Guo Zhou ◽  
Liang Li ◽  
Tai Chao Su ◽  
Shang Sheng Li
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Intermediate Products ◽  
Diamond Particles ◽  
Ternary Carbide ◽  
The Matrix

Ti3SiC2, a ternary carbide, was proposed at this paper to use as the binder of polycrystalline diamonds to overcome the weaknesses of traditional metal binders and ceramic binders. Ti3SiC2was first reported to be in-situ synthesized under high pressure (4GPa) and at high temperature (1400°C) (HPHT) from the mixtures of Ti, Si and graphite powders or the mixture of Ti, SiC and graphite powders. Ti3SiC2-damond composites were also made at HPHT from the previous mixtures and diamond particles. TiCx, Ti5Si3Cxand TiSi2were main impurities and/or intermediate products of Ti3SiC2samples synthesized at HPHT. Ti3SiC2content increased as synthesized time increased from 10 min to 60 min. For as-synthesized composites, diamond particles were evenly distributed in matrix. The diamond particles are bonded well with the matrix by three types of interface.

The Investigation on Aluminium Alloys Automobile Wheel with Low-Titanium Content Produced by Electrolysis

2005 ◽  
Vol 475-479 ◽  
pp. 317-320 ◽  
Author(s):  
Jing Pei Xie ◽  
Ji Wen Li ◽  
Zhong Xia Liu ◽  
Ai Qin Wang ◽  
Yong Gang Weng ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Aluminium Alloys ◽  
Solution Treatment ◽  
A356 Alloy ◽  
Aging Treatment ◽  
Titanium Content ◽  
The Matrix ◽  
Automobile Wheel

The in-situ Ti alloying of aluminium alloys was fulfilled by electrolysis, and the material was made into A356 alloy and used in automobile wheels. The results show that the grains of the A356 alloy was refined and the second dendrites arm was shortened due to the in-situ Ti alloying. Trough 3-hour solution treatment and 2-hour aging treatment for the A356 alloy, the microstructures were homogeneous, and Si particles were spheroid and distribute in the matrix fully. The outstanding mechanical properties with tensile strength (σb≥300Mpa) and elongation values (δ≥10%) have been obtained because the heat treatment was optimized. Compared with the traditional materials, tensile strength and elongation were increased by 7.6~14.1% and 7.4~44.3% respectively. The qualities of the automobile wheels were improved remarkably.

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