8,735 research outputs found
High-Precision Optical Measurement of the 2S Hyperfine Interval in Atomic Hydrogen
We have applied an optical method to the measurement of the 2S hyperfine
interval in atomic hydrogen. The interval has been measured by means of
two-photon spectroscopy of the 1S-2S transition on a hydrogen atomic beam
shielded from external magnetic fields. The measured value of the 2S hyperfine
interval is equal to 177 556 860(15) Hz and represents the most precise
measurement of this interval to date. The theoretical evaluation of the
specific combination of 1S and 2S hyperfine intervals D_21 is in moderately
good agreement with the value for D_21 deduced from our measurement
Bayesian evaluation of the southern hemisphere radiocarbon offset during the holocene
While an interhemispheric offset in atmospheric radiocarbon levels from AD 1950â950 is now well established, its existence earlier in the Holocene is less clear, with some studies reporting globally uniform 14C levels while others finding Southern Hemisphere samples older by a few decades. In this paper, we present a method for wiggle-matching Southern Hemisphere data sets against Northern Hemisphere curves, using the Bayesian calibration program OxCal 4.1 with the Reservoir Offset function accommodating a potential interhemispheric offset. The accuracy and robustness of this approach is confirmed by wiggle-matching known-calendar age sequences of the Southern Hemisphere calibration curve SHCal04 against the Northern Hemisphere curve IntCal04. We also show that 5 of 9 Holocene Southern Hemisphere data sets are capable of yielding reliable offset information. Those data sets that are accurate and precise show that interhemispheric offset levels in the Early Holocene are similar to modern levels, confirming SHCal04 as the curve of choice for calibrating Southern Hemisphere samples
Incompatible blood transfusions in liver transplant patients with significant red cell alloantibodies
Tools made of ice facilitate forming of soft, sticky materials
Tools made of ice facilitate the forming or shaping of materials that are soft and sticky in the uncured state. The low-temperature of the ice slows the curing of the material, extending the working time available before setup. Handling problems are eliminated because the material does not adhere to the tool, and the melting ice serves as a lubricant
Revised calendar date for the Taupo eruption derived by ÂčâŽC wiggle-matching using a New Zealand kauri ÂčâŽC calibration data set
Taupo volcano in central North Island, New Zealand, is the most frequently active and productive rhyolite volcano on Earth. Its latest explosive activity about 1800 years ago generated the spectacular Taupo eruption, the most violent eruption known in the world in the last 5000 years. We present here a new accurate and precise eruption date of AD 232 ± 5 (1718 ± 5 cal. BP) for the Taupo event. This date was derived by wiggle-matching 25 high-precision ÂčâŽC dates from decadal samples of Phyllocladus trichomanoides from the Pureora buried forest near Lake Taupo against the high-precision, first-millennium AD subfossil Agathis australis (kauri) calibration data set constructed by the Waikato Radiocarbon Laboratory. It shows that postulated dates for the eruption estimated previously from Greenland ice-core records (AD 181 ± 2) and putative historical records of unusual atmospheric phenomena in ancient Rome and China (c. AD 186) are both untenable. However, although their conclusion of a zero northâsouth ÂčâŽC offset is erroneous, and their data exhibit a laboratory bias of about 38 years (too young), Sparks et al. (Sparks RJ, Melhuish WH, McKee JWA, Ogden J, Palmer JG and Molloy BPJ (1995) ÂčâŽC calibration in the Southern Hemisphere and the date of the last Taupo eruption: Evidence from tree-ring sequences. Radiocarbon 37: 155â163) correctly utilized the Northern Hemisphere calibration curve of Stuiver and Becker (Stuiver M and Becker B (1993) High-precision decadal calibration of the radiocarbon timescale, AD 1950â6000 BC. Radiocarbon 35: 35â65) to obtain an accurate wiggle-match date for the eruption identical to ours but less precise (AD 232 ± 15). Our results demonstrate that high-agreement levels, indicated by either agreement indices or ÏÂČ data, obtained from a ÂčâŽC wiggle-match do not necessarily mean that age models are accurate. We also show that laboratory bias, if suspected, can be mitigated by applying the reservoir offset function with an appropriate error value (e.g. 0 ± 40 years). Ages for eruptives such as Taupo tephra that are based upon individual ÂčâŽC dates should be considered as approximate only, and confined ideally to short-lived material (e.g. seeds, leaves, small branches or the outer rings of larger trees)
Drought Injuries to Evergreen Trees in Windbreaks in Iowa
As in all the Plains states, in Iowa the first windbreaks were of the quicker growing species of trees. Cottonwoods, boxelders, willows and silver maples were heavy favorites several decades ago when farm homes began to dot the prairies, but after a few years when these trees began to lose what little ability they did have in wind protection, the Iowa farmers considered trees oÂŁ more lasting qualities and more ability to check and effectively block the bitter winds of winter
Teachers\u27 Perceptions of the Multiage Program at Kingsley Elementary School in Sullivan County, Tennessee
This study examines how teachers at Kingsley Elementary School feel about the multiage program now as compared to when the program was first implemented. There were 28 teachers and two administrators interviewed to determine their perceptions of the positive and negative influences of the multiage program. The purpose of the study is to reveal the success or failure of the multiage program at Kingsley Elementary School and to explore the process used by the school to implement the process. The approach to this study is qualitative and uses interview data from both former and current Kingsley staff. Five research questions were formulated. The field effort concentrated on the respondents\u27 perceptions of the developmental process of the multiage program. Results suggest that the teachers\u27 and administrators\u27 perceptions of the multiage program at Kingsley Elementary School are basically for traditional methods. During the analysis, suggestions emerged from the interviewees to improve the multiage program. Some of these suggestions could be used as a guide for other school systems that are beginning implementation of a multiage program
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