4,260 research outputs found
A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years
The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its ^(14)C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere (∼110‰∼110‰) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ^(14)C can also be found in Greenland ice core δ^(18)O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales
Readout of solid-state charge qubits using a single-electron pump
A major difficulty in realizing a solid-state quantum computer is the
reliable measurement of the states of the quantum registers. In this paper, we
propose an efficient readout scheme making use of the resonant tunneling of a
ballistic electron produced by a single electron pump. We treat the measurement
interaction in detail by modeling the full spatial configuration, and show that
for pumped electrons with suitably chosen energy the transmission coefficient
is very sensitive to the qubit state. We further show that by using a short
sequence of pumping events, coupled with a simple feedback control procedure,
the qubit can be measured with high accuracy.Comment: 5 pages, revtex4, 4 eps figures. v2: published versio
Nanotransfer Printing of Organic and Carbon Nanotube Thin-Film Transistors on Plastic Substrates
A printing process for high-resolution transfer of all components for organic
electronic devices on plastic substrates has been developed and demonstrated
for pentacene (Pn), poly (3-hexylthiophene) and carbon nanotube (CNT) thin-film
transistors (TFTs). The nanotransfer printing process allows fabrication of an
entire device without exposing any component to incompatible processes and with
reduced need for special chemical preparation of transfer or device substrates.
Devices on plastic substrates include a Pn TFT with a saturation, field-effect
mobility of 0.09 cm^2 (Vs)^-1 and on/off ratio approximately 10^4 and a CNT TFT
which exhibits ambipolar behavior and no hysteresis.Comment: to appear in Applied Physics Letter
Characterization of Melt Infiltrated SiC/SiC Composite Combustor Liners Using Meso- and Micro-NDE Techniques
Melt-infiltrated ceramic matrix composite SiC/SiC material systems are under development for use in combustor liners for low-emission advanced gas turbines. Uncertainty in repeatability of processing methods for these large components (33--76 cm diameter), and hence possible reduced reliability for the end user. This requires that appropriate test methods, at both meso- and micro-scale, be used to ensure that the liners are acceptable for use. Nondestructive evaluation (NDE) methods, if demonstrated to reliably detect changes caused by processing, would be of significant benefit to both manufacturer and end user. This paper describes the NDE methods and their applications in detecting a process upset in a melt-infiltrated 33 cm combustor liner and how high-resolution scanning electron microscopy was used to verify the NDE data
Spitzer/MIPS Observations of Stars in the Beta Pictoris Moving Group
We present Multiband Imaging Photometer for Spitzer (MIPS) observations at 24
and 70 microns for 30 stars, and at 160 microns for a subset of 12 stars, in
the nearby (~30 pc), young (~12 Myr) Beta Pictoris Moving Group (BPMG). In
several cases, the new MIPS measurements resolve source confusion and
background contamination issues in the IRAS data for this sample. We find that
7 members have 24 micron excesses, implying a debris disk fraction of 23%, and
that at least 11 have 70 micron excesses (disk fraction of >=37%). Five disks
are detected at 160 microns (out of a biased sample of 12 stars observed), with
a range of 160/70 flux ratios. The disk fraction at 24 and 70 microns, and the
size of the excesses measured at each wavelength, are both consistent with an
"inside-out" infrared excess decrease with time, wherein the shorter-wavelength
excesses disappear before longer-wavelength excesses, and consistent with the
overall decrease of infrared excess frequency with stellar age, as seen in
Spitzer studies of other young stellar groups. Assuming that the infrared
excesses are entirely due to circumstellar disks, we characterize the disk
properties using simple models and fractional infrared luminosities. Optically
thick disks, seen in the younger TW Hya and eta Cha associations, are entirely
absent in the BPMG.
Additional flux density measurements at 24 and 70 microns are reported for
nine Tucanae-Horologium Association member stars. Since this is <20% of the
association membership, limited analysis on the complete disk fraction of this
association is possible.Comment: Accepted for Ap
Assessing Preemptive Argumentation in Students’ Persuasive Speech Outlines
The purpose of the present study was to determine if critical thinking skills, a key component of basic communication course pedagogy, can be assessed through students’ use of preemptive argumentation. Persuasive speech outlines were coded to determine if preemptive argumentation was present in students’ speeches and to determine the quality of preemptive argumentation. The results indicated that the majority of outlines contained preemptive argumentation. However, of those speeches containing preemptive argumentation, the majority of outlines employed low-quality preemptive argumentation. Finally, the findings revealed that the quality of preemptive argumentation employed in the persuasive speech outlines did not predict the students’ persuasive speech grades. Implications for instructor training programs and pedagogy in the basic course are discussed
Comparison of Methods for Purification of DNA From Rice
Three techniques were employed to purify genomic DNA from deomstic rice (Oryza sativa L). Following extraction, the DNA was electrophoresed through agarose to determine its integrity. We determined that spooling yielded better quality, through lower quantity DNA than either of the other two techniques
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