345 research outputs found
Using the typewriter as a motivational tool with the learning disabled
The study was concerned with reviewing the current literature relating to typewriting in the exceptional education and general education areas during the past seven years
Design, construction and commissioning of a high-flow radon removal system for XENONnT
A high-flow radon removal system based on cryogenic distillation was
developed and constructed to reduce radon-induced backgrounds in liquid xenon
detectors for rare event searches such as XENONnT. A continuous purification of
the XENONnT liquid xenon inventory of 8.4 tonnes at process flows up to 71 kg/h
(200 slpm) is required to achieve a radon reduction by a factor two for radon
sources inside the detector. To reach such high flows, the distillation
column's design features liquid xenon inlet and outlets along with novel
custom-made bath-type heat exchangers with high liquefaction capabilities. The
distillation process was designed using a modification of the McCabe-Thiele
approach without a bottom product extraction. The thermodynamic concept is
based on a Clausius-Rankine cooling cycle with phase-changing medium, in this
case the xenon itself. To drastically reduce the external cooling power
requirements, an energy efficient heat pump concept was developed applying a
custom-made four cylinder magnetically-coupled piston pump as compressor. The
distillation system was operated at thermodynamically stable conditions at a
process flow of (912) kg/h ((2586) slpm), 30 % over design. With this
flow, a Rn activity concentration <1 Bq/kg is expected inside the
XENONnT detector given the measured radon source distribution
Cryogenic bath-type heat exchangers for ultra-pure noble gas applications
Two cryogenic bath-type heat exchangers for ultra-pure noble gas applications were developed with particular emphasis on noble gas liquefaction in cryogenic distillation systems. The main objective was to construct heat exchangers for xenon from materials that do not emanate radon and that fulfill ultra-high vacuum standards. Therefore, only high-quality copper and stainless steel materials were used. Especially, large-area oxygen-free copper fins with high conductivity in a new design ensure efficient heat transfer. One bath-type Xe-Xe heat exchanger was designed with a diameter of 50 cm to achieve a xenon condensing capacity of at least 100 kg/h. In order to guarantee the necessary heat transfer between the two xenon reservoirs, this heat exchanger features a specially manufactured stainless steel flange with a copper plate welded inside. We first tested our concept on a dedicated bath-type heat exchanger with a reduced diameter of 30 cm using liquid nitrogen to liquefy the xenon. A model based on conservative assumptions such as film boiling on the nitrogen side and film condensation on the xenon side was developed and applied to caluclate the expected heat transfer for our design. We were able to demonstrate an adjustable xenon liquefaction rate of up to 113 kg/h limited only by our measurement procedure at a cooling efficiency of (0.98 ± 0.03) for the LN-Xe heat exchanger
The continental assembly of SW Gondwana (Ediacaran to Cambrian): a synthesis
SW Gondwana resulted from complex interplay between continental amalgamation and
dispersal between ~ 650 and 490 Ma. The main cratons involved were Laurentia, Amazonia–
MARA (Proterozoic Maz–Arequipa–Rio Apa, Casquet et al., 2012), Kalahari, Rio de la Plata
(RPC), Congo and East Antarctica (Mawson block). Several collisional orogenic belts resulted,
notably the East Africa–Antarctica, Brasiliano–Panafrican, Pampean–Saldania, and Ross–
Delamerian orogens.
East-Antarctica broke away from the western margin of Laurentia in Rodinia. After a long drift
and counter-clockwise rotation (Dalziel, 2013) it collided with Congo and Kalahari to produce
the southern part of the left-lateral transpressional East Africa–Antarctica orogen between
580 and 550 Ma, completing the amalgamation of East Gondwana. The Trans-Antarctic
margin became an active one in the Ediacaran and subduction of the Pacific Ocean lithosphere
occurred throughout the Paleozoic, forming a tract of the Terra Australis orogen. NW–SE
directed compression in Late Cryogenian and Early Ediacaran times promoted closure of the
Adamastor Ocean, resulting in the left-lateral transpressional Brasiliano–Pan African orogeny
between 650 and 570 Ma.
The Pampean orogenic belt to the west of the RPC resulted from right-lateral collision between
Laurentia and its eastern extension MARA on the one hand and Kalahari–RPC on the other.
Ocean opening started at ~ 630 Ma and subduction and further collision took place between
540 and 520 Ma, coeval with the northward drift of Laurentia (~ 540 Ma) away from MARA
and the consequent formation of the proto-Andean margin of Gondwana. The margins of the
intervening Puncoviscana ocean were covered by Laurentia-derived siliciclastic sediments and
carbonates on the MARA side between 630 and ~ 540 Ma (Rapela et al, 2014; this symposium),
and by the marine siliciclastic Puncoviscana Formation on the other. The latter formation,
deposited between a 570 and ~530 Ma, received input from large alluvial fans descending
from juvenile Mesoproterozoic and Neproterozoic sources (new Hf isotope evidence) largely
located in the southern East Africa–Antarctica orogen. The Pampean orogen extended into
the Saldania–Gariep orogen of southern South Africa (545–520 Ma) and was apparently
discordant to the earlier Brasiliano–Pan African orogen. In late-Early to late Cambrian times the
Pampean–Saldania realm evolved into a passive margin with siliciclastic platform sedimentation.
The Pampean-Saldania realm was separated from the active Trans-Antarctic margin of East
Antarctica by an inferred transform fault in Ediacaran to Cambrian times. Regional NW–SW
shortening in the Ediacaran became N–S directed in the Cambrian, suggesting a major plate
reorganization at this time.Peer reviewe
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