Strain History and Short-Period Aging Effects on the Strength and Cyclic Response of Fine-Grained Coal Refuse

A constitutive law is developed for metals which have aging properties. The development of this law is based on the assumption that the mechanical properties of simple aging materials can be mathematically represented by a functional of the strain history, and that this functional depends upon the age of the material. A perturbation technique allows the separation of the nonaging response from the aging effects, and leads to convenient representations for viscoelasticity and plasticity. The mechanical behavior of aging metals is studied by applying the arc length parameterization of the strain history. The final rate independent results are transformed to the time domain for efficient use in engineering applications and in solving boundary value problems.

Download Full-text

Interstellar and Solar System organic matter preserved in interplanetary dust

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316005718 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 426-426

Author(s):

Scott Messenger ◽

K. Nakamura-Messenger

Keyword(s):

Organic Matter ◽

Solar System ◽

Carbonaceous Material ◽

Interplanetary Dust ◽

Dust Particles ◽

Interplanetary Dust Particles ◽

Fine Grained ◽

Mass Fractionation ◽

Current State ◽

Short Period

AbstractInterplanetary dust particles (IDPs) collected in the Earths stratosphere derive from collisions among asteroids and by the disruption and outgassing of short-period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP-IDPs have been linked to cometary parent bodies by their mineralogy, textures, C-content, and dynamical histories. CP-IDPs are fragile, fine-grained (< um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP-IDPs, constituting 0.01-1% of the mass of the particles. The organic matter in CP-IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10-100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub-um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub-um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild-2 samples returned by the Stardust mission. We will present an overview of the current state of understanding of the properties and origins of organic matter in primitive IDPs.

Download Full-text

Spark Plasma Sintering TiAl Alloy from Mechanically Activated Powders

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.250-253.3309 ◽

2011 ◽

Vol 250-253 ◽

pp. 3309-3312 ◽

Cited By ~ 1

Author(s):

Zhi Wei Wang ◽

Hong Cheng ◽

Hui Ming Cheng

Keyword(s):

Spark Plasma Sintering ◽

Tial Alloy ◽

Sintering Temperature ◽

Al Alloy ◽

Tial Alloys ◽

Fine Grained ◽

Plasma Sintering ◽

Short Period ◽

Spark Plasma ◽

Higher Temperature

Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Download Full-text

TiAl Alloy Spark Plasma Sintered from Mechanically Activated Powders

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.284-286.2336 ◽

2011 ◽

Vol 284-286 ◽

pp. 2336-2339

Author(s):

Zhi Wei Wang ◽

Jun Chen

Keyword(s):

Spark Plasma Sintering ◽

Tial Alloy ◽

Sintering Temperature ◽

Al Alloy ◽

Tial Alloys ◽

Fine Grained ◽

Plasma Sintering ◽

Short Period ◽

Spark Plasma ◽

Higher Temperature

Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Download Full-text

Evaluation of Dynamic Methods for Earthwork Assessment

Civil and Environmental Engineering ◽

10.1515/cee-2015-0005 ◽

2015 ◽

Vol 11 (1) ◽

pp. 38-44 ◽

Cited By ~ 6

Author(s):

Jozef Vlček ◽

Dominika Ďureková ◽

Katarína Zgútová

Keyword(s):

Boundary Conditions ◽

Quality Evaluation ◽

Civil Engineering ◽

Rapid Development ◽

Road Construction ◽

Fine Grained ◽

Dynamic Methods ◽

Short Period ◽

Parallel Measurements ◽

Construction Works

Abstract Rapid development of road construction imposes requests on fast and quality methods for earthwork quality evaluation. Dynamic methods are now adopted in numerous civil engineering sections. Especially evaluation of the earthwork quality can be sped up using dynamic equipment. This paper presents the results of the parallel measurements of chosen devices for determining the level of compaction of soils. Measurements were used to develop the correlations between values obtained from various apparatuses. Correlations show that examined apparatuses are suitable for examination of compaction level of fine-grained soils with consideration of boundary conditions of used equipment. Presented methods are quick and results can be obtained immediately after measurement, and they are thus suitable in cases when construction works have to be performed in a short period of time.

Download Full-text

Synthesizing TiAl Alloy by Spark Plasma Sintering from Mechanically Activated Powders

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.233-235.2769 ◽

2011 ◽

Vol 233-235 ◽

pp. 2769-2772

Author(s):

Zhi Wei Wang ◽

Zhi Xiang Bu ◽

Li Shi Wang

Keyword(s):

Spark Plasma Sintering ◽

Tial Alloy ◽

Sintering Temperature ◽

Al Alloy ◽

Tial Alloys ◽

Fine Grained ◽

Plasma Sintering ◽

Short Period ◽

Spark Plasma ◽

Higher Temperature

Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Download Full-text

The Impact of Short-Term Dietary Restriction on Stem Cell Function

Innovation in Aging ◽

10.1093/geroni/igab046.443 ◽

2021 ◽

Vol 5 (Supplement_1) ◽

pp. 116-117

Author(s):

Archana Unnikrishnan

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Dietary Restriction ◽

Cell Function ◽

Aging Effects ◽

Short Term ◽

Regenerative Capacity ◽

Short Period ◽

The Impact ◽

Old Mice

Abstract Stem cells play a critical role in the maintenance of tissue function and their proliferative/regenerative capacity is essential to this role. Because stem cells persist over the lifespan of an animal, they are susceptible to gradual accumulation of age-associated damage, resulting in the loss of regenerative function that can impair organ function. Understanding the mechanism(s) that regulates stem cell function is essential for retarding the aging process, and stem cells are attractive targets for aging interventions. Dietary restriction (DR), the most robust anti-aging intervention to-date, has been shown to enhance the activity and integrity of stem cells in a variety of tissues (e.g., muscle, bone marrow, and intestine), and it is believed that effect of DR on stem cells plays an important role in the anti-aging action of DR. For example, DR has been shown to preserve and increase the number of intestinal stem cells (ISCs) and enhance their regenerative capacity in young animals. Data from my lab shows that ISCs from old mice have limited proliferation activity and form few if any organoids in vitro (a surrogate for a fully functional crypt) and that ISCs isolated from old mice on life-long DR show an improved ability to form organoids. While it is well accepted that life-long DR increases lifespan and has anti-aging effects an important aspect of DR that has been largely overlooked is that DR implemented only for a short time early in life can increase lifespan of rodents even when rodents are fed ad libitum the remainder of their life. In line with this, we recently found that ISCs from old mice fed DR for only a short-period resulted in a dramatic increase in ability of the ISCs to form organoids. This is the first evidence that short-term DR administrated late in life can rescue the loss in ISC function that occurs with age.

Download Full-text

MODELLING OF AGING OF THREADS AND FIBRES WITH COMPUTER SIMULATION METHODS

Technologies & Quality ◽

10.34216/2587-6147-2019-4-46-36-39 ◽

2019 ◽

pp. 36-39

Author(s):

P. A. Sevost'yanov

Keyword(s):

Statistical Simulation ◽

Software Implementation ◽

Simulation Methods ◽

Fibrous Materials ◽

Aging Effects ◽

Factors Affecting ◽

One Dimensional ◽

Short Period ◽

Stationary Conditions ◽

Probabilistic Nature

The article proposes an algorithm for computer statistical simulation of the formation and development of areas of defects and aging in one-dimensional fibrous materials of arbitrary finite length. The software implementation of the algorithm in the Matlab environment allowed to obtain a visual picture of the aging regions propagation dynamics, taking into account the probabilistic nature of the occurrence and propagation of defects. The model combines factors affecting the location of defect sources along the threads and fibres length, the violation intensity of the fibrous material properties in the defective areas, and the speed of its propagation along the threads and fibres length. The developed model allows to study the influence of numerous factors on the aging effects dynamics in one-dimensional materials, to rank the degree of their influence, to determine the area of efforts for the aging processes study in full-scale experiments. An example is given for realisations of defects along the length of the sample for stationary and non-stationary conditions of the thread aging, when within a short period of time the thread was subjected to intense exposure, which contributed to the acceleration of aging and destruction.

Download Full-text

Preparation of Dense Ultrafine TiAl Alloys by Spark Plasma Synthesis from Mechanically Activated Powders

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.217-218.1747 ◽

2011 ◽

Vol 217-218 ◽

pp. 1747-1752

Author(s):

Zhi Wei Wang ◽

Dong Dong Zhang ◽

Xiu Hong Zhang

Keyword(s):

Spark Plasma Sintering ◽

Sintering Temperature ◽

Al Alloy ◽

Plasma Synthesis ◽

Tial Alloys ◽

Fine Grained ◽

Plasma Sintering ◽

Short Period ◽

Spark Plasma ◽

Spark Plasma Synthesis

Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Download Full-text

Jeitun: Recent Excavations at an Early Neolithic Site in Southern Turkmenistan

Proceedings of the Prehistoric Society ◽

10.1017/s0079497x00002863 ◽

1996 ◽

Vol 62 ◽

pp. 423-442 ◽

Cited By ~ 14

Author(s):

D.R. Harris ◽

C. Gosden ◽

M.P. Charles

Keyword(s):

Detailed Examination ◽

Radiocarbon Dates ◽

Collaborative Project ◽

Fine Grained ◽

Neolithic Site ◽

Animal Remains ◽

Recovery Techniques ◽

Short Period ◽

History Of ◽

History Of Use

Excavations at the Neolithic site of Jeitun in Turkmenistan, Central Asia, were carried out by a British team between 1991 and 1994 as part of a collaborative project with Soviet and Turkmenian archaeologists. Jeitun was first systematically excavated in the 1950s by Professor V.M. Masson and was shown to be a small settlement of mudbrick houses and ancillary buildings together with yard layers. Our recent excavations have attempted to refine knowledge of the site's stratigraphy and architecture by using fine-grained excavation and recovery techniques and by sampling systematically for sediments, plant and animal remains, and artefacts. We have also obtained the first suite of radiocarbon dates from the site which shows that it was first occupied at c. 6000 cal. BC and may only have remained in use for a few centuries. The excavations have uncovered the lowest architectural phases at Jeitun, as demonstrated by detailed examination of two houses at the northern end of the site. Both houses have a complex history of use, with well laid gypsum floors and intervening layers of sand and mudbrick destruction. Such complexity may indicate that the site was not occupied permanently, although year-round occupation is, on present evidence, equally likely. We tentatively define three phases in the occupation of the site, from ephemeral use in the lowest layers to complex and intensive occupation in the uppermost parts. These phases cannot be separated by the 11 radiocarbon dates obtained, which appear to suggest that activity at the site increased relatively rapidly over a short period of time. Further excavation and analysis is needed to refine and strengthen our conclusions.

Download Full-text