Ar Method Research Articles

Formation of Holes in Engineering Ceramic Plates by Press-Working

The purpose of the present research is to establish a simple method of forming holes in brittle materials by a conventional press-working. By utilizing a specially designed blunted spherical punch, a small hole is formed at the center of the specimen at its first stage, and subsequently the hole is enlarged by a continuous punching operation. The present improved technique realizes a very low load for punching operation as well as a considerably low clamping stress for preventing serious radial cracks around the hole. Some punching works in engineering ceramic plates were performed by the method for various aspect ratios AR=3∼32(AR=D/t, D; the diameter of the hole and t; the plate thickness). As long as the AR value is larger than about 3, the present method proved to be very successful in forming holes in tough engineering ceramics such as alumina, silicon-nitride and toughend zirconia, as well as in making small holes less than 1 mm in diameter. The technique is also successful in forming many holes by a single operation.

Multi-method dating comparison for mid-pleistocene Rangitawa Tephra, New Zealand

The Rangitawa Tephra, a widespread mid-Pleistocene marker in the New Zealand region, is dated by fission-track, thermoluminescence (TL), infrared stimulated luminescence (IRSL), K Ar and single crystal laser fusion (SCLF) 40 Ar 39 Ar methods, as well as by matching to the astronomical timescale via oxygen isotope stratigraphy in deep sea cores. Fifty one independent numerical age estimates for Rangitawa Tephra range from 173 to 456 ka. However, only 15 of these results are considered to be reliable: five zircon fission-track results, four isothermal plateau fission-track (ITPFT) age estimates on glass shards, four SCLF 40 Ar 39 Ar results, and two astronomically calibrated age estimates from deep sea cores. The weighted mean of the nine reliable fission-track age determinations is 345 ± 12 ka, in excellent agreement with the weighted mean of 340 ± 7 ka for the two reliable astronomically calibrated age estimates. The weighted mean of the four reliable 40 Ar 39 Ar results (302 ± 8 ka) is significantly younger, and further Ar Ar dating is recommended to investigate this difference. Since the TL and IRSL dating methods are experimental for sediments beyond 200 ka, we have excluded these from the group of reliable age results. TL and IRSL results on dunesand appear to be systematically younger than TL results on loess, and loess results depend upon analytical procedures.

Miocene NNE-directed extensional unroofing in the Menderes Massif, southwestern Turkey

Structural investigations in the central part of the Menderes Massif (Ödemiº-Kiraz submas-sif) reveal the presence of a large-scale, low-angle extensional shear zone with a top-to-the-N-NE shear sense. Regional ductile deformation was accompanied by the intrusion of two syntectonic granodiorites that have been dated with the 40 Ar/ 39 Ar method. One hornblende isochron age of 19.5 ± 1.4 Ma and two biotite plateau ages of 13.1 ± 0.2 and 12.2 ± 0.4 Ma, respectively, constrain that extension was already active in the early Miocene. Successive tectonic denudation of the Ödemiº-Kiraz submassif resulted in the formation of a N-dipping detachment fault, in which ductile fabrics were severely reworked by cataclasis under decreasing temperature. Syntectonic Neogene sediments, currently exposed along the southern margin of the Gediz Graben, were deposited in the hanging wall of the extensional fault system and were tectonically emplaced onto the cataclasites during progressive exhumation. Minor rotation (< 15°) of the detachment fault to its present gentle dip of c . 15° caused southward tilting of the sediments. Ongoing NNE-directed extension created a steep normal fault that truncates the detachment fault and constitutes the southern boundary fault of the Gediz Graben.

The age of Acadian cleavage in northern England, UK: K–Ar and TEM analysis of a Silurian metabentonite

SUMMARY K–Ar and 40 Ar– 39 Ar isotope analysis and transmission electron microscopy were used to study the cleavage developed in a metabentonite during the Acadian tectonometamorphic event in northern England. The Foredale metabentonite, from the Ribblesdale inlier in the Pennines, is one of numerous K-bentonites preserved in the hemipelagic Horton Formation of Lower Ludlow (Gorstian) age. It consists of over 90% phengitic white mica crystallized during deformation and cleavage development under mid-anchizonal metamorphic conditions. Temperatures approaching 250°C combined with strain energy to completely eliminate original smectite interlayers, producing stable crystallites of 1M and 2M mica polytypes. Mica concentrates analysed by the K–Ar method have a weighted mean apparent age of 397 ± 7 Ma; 40 Ar– 39 Ar total fusion analyses have a weighted mean apparent age of 418 ± 3 Ma. The true cleavage-forming event lies within this age range. An inferred geothermal gradient of <25°Ckm −1 , based on the white mica b lattice dimension, suggests that the Foredale metabentonite was buried under at least 10km of overburden, much of it Lower Old Red Sandstone, prior to late Lower Devonian (Emsian) uplift in northern England.

KAr chronology of a Mesozoic dike swarm from southern Espinhaço Region (SE Brazil)

Dikes which cut Archean and Proterozoic sequences and the Brasiliano structures in the Southern Espinhaço Region were dated using the conventional KAr method. The particular petrographic characteristics of the swarm in relation to those of the Precambrian, abundant in the region, provide no evidence of deformation or metamorphism. The geochronological results indicate that emplacement of the dikes was related to the Mesozoic extensional tectonics and point to a period of magmatic activity during Upper Triassic/Lower Jurassic, between 170 and 220 Ma. Data indicate that the swarm is earlier than the main Phanerozoic swarms of southeast Brazil which are related to the opening of the South Atlantic, and that the dikes were emplaced during the initial breakup of Gondwana.

Formation of Holes in Engineering Ceramic Plates by Press-Working. Formation Patterns and Practical Applications.

One of the authors has developed a punching method of brittle materials by utilizing a specially designed round-top punch in conventional press-working. We aim to study the mechnism of hole-punching and also to investigate the possibility of practical use of the method. Some experimental punching work in engineering ceramic plates was performed by the method for various aspect ratios AR=3∼65 (AR=D/t, D ; the diameter of the hole and t ; the plate thickness). As long as the AR value is larger than about 3, the present method proved to be very successful in forming holes in tough engineering ceramics such as alumina, silicon-nitride and toughened zirconia, as well as in making small holes less than 1mm in diameter.

On the performance of different AR methods in the spectral estimation of FDTD waveforms

AbstractIn the past, several extrapolation techniques have been used in conjunction with the finite‐difference—time‐domain algorithm to reduce the computational cost involved in obtaining an accurate representation of the frequency response of the electromagnetic system under consideration. In this article we study the performances of different autoregressive techniques in accurately estimating the spectra of finite‐difference—time‐domain waveforms without resorting to extrapolation. The advantages and disadvantages of these techniques are demonstrated through two examples: a package plane structure and a cavity. © 1994 John Wiley & Sons, Inc.

Excess argon in phengite from eclogite: Evidence from dating of eclogite minerals by SmNd, RbSr and [formula omitted] methods

The existence of excess Ar in phengites from coesite-bearing ultrahigh-pressure eclogites of the Dabie Mountains and SuLu terrain, China, has been confirmed by dating of minerals using SmNd, RbSr and 40 Ar 39 Ar methods. 40 Ar 39 Ar ages of phengites for two samples studied are much older than the SmNd and RbSr mineral isochron ages: sample QL- 1 has RbSr age of 219.5 ± 0.5 Ma, SmNd age of 226.3 ± 4.5 Ma and phengite 40 Ar 39 Ar age of 877.5 ± 15.9 Ma; the corresponding ages for sample Zb- 4 are: 223.9 ± 0.9 Ma (RbSr), 228.4 ± 6.0 Ma ( Sm Nd) and 943.3 ± 12.4 Ma ( 40 Ar 39 Ar , phengite). An age of ∼225 Ma based on the SmNd and RbSr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the North China and Yangtse Blocks and formation of these eclogites. We call for greater caution in 40 Ar 39 Ar dating of phengites from other occurrences of ultrahigh-pressure environments.

A Comparison of Methods for Estimating a Transfer Function.

Three methods for estimating a transfer function of a system with two inputs were compared. The first is a method based on the analysis in frequency domain (FD method). The second method makes use of the autoregressive model (AR method). The third one uses the multiple regression model (MR method). These methods were applied to 100 pairs of artificial data which were synthesized on the basis of three kinds of assumed transfer functions. It is concluded from the results of comparison that MR method is the best of the three.

New evidence for cenozoic resetting of KAr ages in volcanic rocks of the Northern Portion of the Armiralty Bay, King George Island, Antarctica

This paper presents six KAr whole-rock ages of the Znosko Glacier Formation (Cardozo Cove Group) that crops out between Mackellar Inlet (type-area) and Ezcurra Inlet, inner Admiralty Bay, King George Island, Antarctica. Originally attributed to the Upper Mesozoic, a RbSr isochron diagram place the lithostratigraphic unit in the Paleocene (60±5 Ma). The same samples were isotopically analyzed by the KAr method and the calculated ages, which range between 40 and 50 Ma, confirm the effect of an important tectonic-thermal event, responsible for structural deformations and metasomatic alterations in that unit. We discuss the origin of the tectonic event and the related KAr reset on rocks cropping out around Admiralty Bay.

Palynology, paleoclimatology and correlation of middle Miocene beds from Porcupine River (locality 90-1), Alaska

Beds in the Upper Ramparts Canyon of the Porcupine River, Alaska (67° 20' N, 141° 20' W), yielded a flora rich in pollen of hardwood genera now found in the temperate climates of North America and Asia. The beds are overlain or enclosed by two basalt flows which were dated to 15.2 ± 0.1 Ma by the 40 Ar 39 Ar method, fixing the period of the greatest abundance of warm-loving genera to the early part of the middle Miocene. The assemblage is the most northern middle Miocene flora known in Alaska. Organic bed 1 underlies the basalt and is older than 15.2 Ma, but is of early to middle Miocene age. The pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood-cypress-yew families with rare occurrences of temperate hardwoods. Organic bed 2 is a forest floor containing redwood trees in life position, engulfed by the lowest basalt flow. A pine log has growth rings up to 1 cm thick. Organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows. Their palynoflora contain conifers and hardwood genera, of which about 40% have modern temperate climatic affinities. Hickory, katsura, walnut, sweet gum, wingnut, basswood and elm pollen are consistently present, and beech and oak alone make up about 20% of the pollen assemblage. A warm high latitude climate is indicated for all of the organic beds, but organic bed 3 was deposited under a time of peak warmth. Climate data derived by comparison with modern east Asian vegetation suggest that, at the time of deposition of organic bed 3, the Mean Annual Temperature (MAT) was ca. 9°C, the Warm Month Mean Temperature (WMMT) was ≥ 20°C and the Cold Month Mean Temperature (CMMT) was ca. −2°C. In contrast, the modern MAT for the region is −8.6°C, WMMT is 12.6°C and CMMT is −28°C. Organic beds 3 and 4 correlate to rocks of the middle Miocene—late Seldovian Stage of Cook Inlet and also probably correlate to, and more precisely date, the lower third of the Suntrana Formation in the Alaska Range, beds at Unalaklect, part of the upper Mackenzie Bay sequence in the Beaufort-Mackenzie basin, and the Mary Sachs gravel of Banks Island. This suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60° and 72°N during the early middle Miocene.

Runoff Process with Short Time Interval Hydrological Data

The flood prediction is difficult because runoff process is distinctly non-linear especially with short time interval hydorological data. Based on the runoff analysis of the 15-minute hydrological data by the filter separation AR method, this paper explains the hydrological runoff process and shows the relationship between pre-flood discharge rate and groundwater infiltration capacity, as well as the relationship between area ratio contributed to runoff and catchment area storage volume.

Collision of the North China and Yangtse Blocks and formation of coesite-bearing eclogites: Timing and processes

Various types of eclogite, including coesite-bearing varieties formed under high- P-high- T conditions (up to 27 kbar, 700–800°C), and glaucophane schist occur in the Dabie Mountains and the SuLu terrane, eastern China. Dating of these high-pressure rocks by the SmNd mineral isochron and 40 Ar 39 Ar method suggests that the occurrence of the high-pressure metamorphism was during the early Triassic. LREE-enriched chondrite-normalized patterns for type-II eclogites and low initial ϵ Nd of − 14 to − 3 and the 87 Sr 86 Sr-values (0.706–0.710) for various types of eclogites suggest that their protoliths were mainly derived from Precambrian island arc or intraplate basalts in the basement of the Yangtse Block and the enriched pyroxenite layer in alpine peridotite. The P-T-t path of eclogite from the southern Dabie Mountains suggests that the uplift history of eclogite in the Dabie Mountains can be subdivided into two stages: (1) fast uplift driven by thrust during continental-continental collision and deep subduction (at 221 Ma) of the continental crust; (2) later gentle uplift with rise of the Dabie Mountains in the late Jurassic and Cretaceous (at 134 Ma). It is proposed that the collision between the North China Block and Yangtse Block began in the late Permian or early Triassic with a north-dipping subduction zone. This was followed by subduction of the continental crust of the Yangtse Block under the North China Block during the Triassic. These two continental blocks were welded into a single tectonic unit in the late Jurassic or early Cretaceous. Different cooling histories for a coexisting gneiss and eclogite pair from Shima area suggest that the eclogite and their country rocks are not always coherent to each other. Some of them may have been juxtaposed through tectonic processes from different levels.

Formation and evolution of the Cigar Lake uranium deposit based on U–Pb and K–Ar isotope systematics

A systematic geochronological study was conducted on the Cigar Lake uranium deposit. U–Pb and Pb–Pb systematics were applied to different types of uranium ore, and various associated sheet silicates were dated by the K–Ar method. These two approaches define a widespread retrograde metamorphic event in the basement, which occurred at about 1780 Ma during the Hudsonian orogeny, and a four-stage evolutionary model for the ore deposit. This model is compatible with the history of other unconformity-type, uranium deposits in the Athabasca Basin.The first stage in the evolution of the Cigar Lake uranium deposit is marked by uraninite crystallization at 1341 ± 17 Ma, which, in association with arsenides and sulpharsenides, constitutes the mineralization of economic interest (main orebody). The second stage, characterized by a Fe-kaolinite and Fe-illite paragenesis, occurred locally at about 900 Ma. The third stage involved uranium mobilization at about 325 Ma and is characterized by (i) preferential loss of radiogenic lead from primary uraninite and crystallization of pitchblende at the rims of uraninite grains and (ii) formation of pitchblende associated with Fe-sulphides or hematite in the main and perched orebodies. The last stage is characterized by recent alteration and coffinitization which have affected all ore types.

Characterisation of ground surface profiles—A comparison of AR, MA and ARMA modelling methods

Grinding is a complex feedback process which could be interpreted as having either the surface or the grinding wheel or both acting as the feedback components. In order to ascertain the appropriateness of each of these models, the surface profile has been modelled using AR, MA and ARMA methods. By drawing an analogy between the feedback models and the mathematical models, the appropriate model is proposed.

Geology and 40 Ar/ 39 Ar geochronology of the Beaver Dam gold deposit, Meguma Terrane, Nova Scotia, Canada; evidence for mineralization at 370 Ma

The Beaver Dam gold deposit, Nova Scotia, Canada, is a lode gold deposit hosted by lower Paleozoic metaturbidites of the Meguma Group; the host rocks were deformed and metamorphosed (greenschist facies) during the Acadian orogeny (dated by the 40 Ar/ 39 Ar method at 400 + or - 10 Ma). The deposit area is located about 2 km east of the River Lake intrusion, a two-mica granodiorite-monzogranite complex of ca. 35 km 2 , and is hosted by intercalated psammites and pelites which occupy the southern, overturned limb (dip 75 degrees N) of the easterly trending Beaver Dam anticline (F 1 ). The pelitic lithologies around the River Lake intrusion contain coarse-grained hornfels (andalusite-garnet-cordierite-staurolite) that overgrow the regional cleavage (S 1 ).The Beaver Dam deposit consists of three subparallel ore zones which contain voluminous amounts of quartz veins of dominantly bedding-concordant nature (lesser discordant vein types occur). The wall rocks contain a greenschist facies mineral assemblage, but in addition subrounded clots (oikocrysts) of coarse quartz-biotite + or - ilmenite + or - calcite + or - sphene + or - chlorite are present which are variably deformed and flattened with high aspect ratios; these may represent variably retrograded andalusite of contact metamorphic origin. Although a single fabric is present in most of the metasedimentary rocks, in the hinge zones of folds an overprint shear cleavage (S 2 ) is observed; this is the same fabric which has flattened the oikocrysts. The veins record two distinct paragenetic stages with an early quartz-calcic plagioclase-biotite-tourmaline (+ or - garnet + or - apatite + or - amphibole) assemblage succeeded by a quartz-calcite-chlorite-muscovite-albite (+ or - anatase) stage. Sulfides (including Bi-Te-Ag sulfides) and gold are predominantly late stage paragenetically. The simple paragenesis is consistent with stable isotope and fluid inclusion data which collectively suggest vein formation during a single hydrothermal event.The relative timing of vein formation is indicated from the following relationships: (1) microveinlets of quartz + calcite crosscut and retrograde the hornfels mineralogy related to the River Lake intrusion, (2) S 2 crenulates S 1 and is axial planar to the folded quartz veins, and (3) the fabric that flattens the oikocrysts is S 2 . Absolute timing of vein formation is inferred to be ca. 370 Ma based on 40 Ar/ 39 Ar age spectra for (1) biotite and muscovite from the River Lake intrusion; (2) muscovite from a pegmatite spatially related to the River Lake intrusion that crosscuts hornfelsic metasediments; and (3) hydrothermal muscovite, biotite, and amphibole from a variety of vein types. The ages are not considered to reflect updating related to the River Lake intrusion but instead to indicate that the vein-forming event postdated regional metamorphism by some 30 m.y. These results would, therefore, invalidate genetic models that related vein formation to regional metamorphism and deformation associated with the 400 + or - 10 Ma Acadian orogeny. Instead, the data support models that relate the mineralization with later thermal and tectonic activity associated with generation of the large granitoid batholiths and late shear zones developed within southern Nova Scotia.

System identification and coherence analysis in the presence of a harmonic signal

This work is concerned with estimation of transfer function and coherence information associated with periodic systems, such as rotating machinery, which involve random processes having infinite as well as finite energy. We propose new complementary spectral-based approaches for system identification and coherence estimation which anticipate this mixture of processes. Their value is demonstrated in a comparative setting, wherein the limitations of FFT and AR methods are highlighted.

Waveshaping filters for spectral estimation of short segments of EEG signals

Least squares waveshaping filters have been used to find the position of energy concentration in an EEG signal. It is shown that this knowledge can be used in obtaining a better spectral estimation of short segments of EEG data. The proposed method is shown to perform better than the conventional AR method.

Mineralogical, KAr and 87Sr/ 86Sr isotope studies of Holocene and Late Glacial sediments in a deep-sea core from the northeast Atlantic Ocean

Fine-grained silicate fractions (<2 μm and 2–16 μm of Holocene and Late Glacial sediments in a deep-sea core from the northeast Atlantic Ocean (47°30′N–19°30′W) have been analysed by X-ray diffraction, KAr and Sr isotopic methods. During the Holocene, the KAr apparent ages and the 87Sr/ 86Sr ratios of the clay size minerals averaged 436 −22 +13 Ma and 0.72638 ± 0.00051, respectively. The KAr values essentially reflect the high 40Ar contribution from the detrital mica in binary smectite-mica mixtures, where smectite is a low potassium and Tertiary-Quaternary component. Higher KAr age value, up to 569 −124 +112 Ma are determined for the coarser 2–16 μm fractions which contain, in addition to mica, other detrital K-bearing phases (amphibole, K-feldspar and plagioclase). An important change in the mineralogical composition and the KAr ages is displayed by the silicate fractions of a thin layer of ice-rafted detritus, located at the termination of the last glaciation. Their KAr apparent ages increase to 773–933 Ma and correspond to an increase of the detrital supply (amphibole, mica and feldspar) from the Precambrian terrains of North America or Greenland and a dilution or a decrease of the input of basaltic material (smectite, oligoclase) from the region of Iceland.

ESR dating of tooth enamel: A comparison with KAr dating

The reliability of the ESR dating of tooth enamel was tested for a famous Italian Palaeolithic site, Isernia la Pineta, already dated by the KAr method. ESR ages, calculated with early uranium uptake model (EU), linear uranium uptake model (LU) and US-ESR model, are between 80 and 251 ka. The US model with the hypothesis of inverse correlation between ESR signal heights and uranium concentration resulted in an age of about 450 ka for one sample. These ages are compared with a KAr age of 736 ka.