3,288 research outputs found
Incidence of Auroras and Their North-South Motions in the Northern Auroral Zone
Studies of the incidence of auroral forms and their north
and south motions are made by using a close-spaced array of
all-sky cameras located in the northern auroral zone at the
approximate geomagnetic longitude 250°E. It is found that during
the observing season 1957-58 the peak of the average auroral
zone occurred at 66-67° geomagnetic latitude. Although the
southern extent of auroras retreats northward after local magnetic
midnight, the southward motion of the individual forms,
observed at the southern edge of the auroral zone, predominates
over the northward motion throughout most of the night. The data
indicate the existence on any given night of a latitude position
near which many auroral forms occur. The first motion of auroras
incident north of this position tends to be northward, and the
first motion of auroras incident south of this position tends
to be southward. A curve showing the occurrence of auroral forms
peaks at, and is nearly symmetrical about, local geographic midnight,
but the intensity of auroral emissions measured over the
celestial hemisphere remains at a high level after midnight.NSP Grant No. Y/22.6/327Ye
A framework for documenting and analyzing life-cycle costs using a simple network based representation
The introduction of high reliability systems combined with
new ways of operating complex systems, particularly in
aircraft design and operation has received much attention in
recent years. Some systems are now being introduced into
service, however, justifying such systems on a financial basis is difficult and may act to limit the rate of introduction on new products.
Conventional life cycle costing based on a hierarchical cost
breakdown structure is poor at recording and analysing the
cost implications of introducing new technologies that have
effects that span more than one phase in the life cycle. There is a risk that too much emphasis is put on âfaithâ that a candidate technology will reduce cost because the cost analysis methods lack descriptive and analytical power.
We describe an approach to representing the costs associated
with introducing new technologies and evaluating their total
cost. Our aim was to facilitate the comparison of different
technological choices in new product development, with a
particular interest in how the perceived benefits of enhanced reliability systems can be shown in a way that is inclusive, objective and easy to understand
Brief Discriptions of Auroral Displays Over Alaska During 1957-58
FOREWORD : This report resulted from the preparation of narrative accounts of
selected auroras to be used as indicated at the 5th CSAGI meeting in
Moscow to complete world-wide descriptions of the major auroras occurring
during the IGY. Since the information utilized in preparing these descriptions
was readily available from other work, completed or underway, it
was logical to expand the descriptions to include all auroras seen during
the observing season 1957-58.
It is intended that this report will serve as a working description
of the auroras incident over Alaska during the period covered. It may
aid in the selection of nights for intensive study as well as providing
information about broad-scale aspects of the aurora when used in conjunction
with other data.NSF Grant No. Y/22.6/327Ye
Posaconazole-induced hypertension and hypokalemia due to inhibition of the 11b-hydroxylase enzyme
The influence of alloy composition on the as-cast grain structure in near net shape low-density steels
Low-density steels are considered an attractive potential replacement for conventional steel in industries such as the automotive sector. However, there are several issues that need to be overcome before they become commercially useful grades. A significant constraint is in their processability, for example, a large as-cast grain size means these steels are prone to hot cracking. This paper explores how compositional variations affect the as-cast grain size in 12 low-density steels cast at solidification rates representative of near net shape casting. It is shown that while mushy zone width is a good indicator of the cast grain size, using a mushy zone width from liquidus to 85% solidified fraction gives a better correlation. It was found that the as-cast grain size of a 7â
wt-% Al steel can be reduced from 736 to 244â
”m through the addition of 1.5â
wt-% Si which acts to increase the mushy zone width by 19°C
Methodological factors influencing measurement and processing of plasma reelin in humans
BACKGROUND: Reelin, intensively studied as an extracellular protein that regulates brain development, is also expressed in a variety of tissues and a circulating pool of reelin exists in adult mammals. Here we describe the methodological and biological foundation for carrying out and interpreting clinical studies of plasma reelin. RESULTS: Reelin in human plasma was sensitive to proteolysis, freeze-thawing and heating during long-term storage, sample preparation and electrophoresis. Reelin in plasma was a dimer under denaturing conditions. Boiling of samples resulted in laddering, suggesting that each of the 8 repeats expressed in reelin contains a heat-labile covalent bond susceptible to breakage. Urinary-type and tissue-type plasminogen activator converted reelin to a discrete 310 kDa fragment co-migrating with the major immunoreactive reelin fragment seen in plasma and also detected in brain. (In contrast, plasmin produced a spectrum of smaller unstable reelin fragments.) We examined archival plasma of 10 pairs of age-matched male individuals differing in repeat length of a CGG repeat polymorphism of the 5'-untranslated region of the reelin gene (both alleles < 11 repeats vs. one allele having >11 repeats). Reelin 310 kDa band content was lower in subjects having the long repeats in all 10 pairs, by 25% on average (p < 0.001). In contrast, no difference was noted for amyloid precursor protein. CONCLUSIONS: Our studies indicate the need for caution in measuring reelin in archival blood samples, and suggest that assays of plasma reelin should take into account three dimensions that might vary independently: a) the total amount of reelin protein; b) the relative amounts of reelin vs. its proteolytic processing products; and c) the aggregation state of the native protein. Reelin-plasminogen activator interactions may affect their roles in synaptic plasticity. Our results also suggest that the human CGG repeat polymorphism affects reelin gene expression, and may affect susceptibility to human disease
CMB power spectrum contribution from cosmic strings using field-evolution simulations of the Abelian Higgs model
We present the first field-theoretic calculations of the contribution made by
cosmic strings to the temperature power spectrum of the cosmic microwave
background (CMB). Unlike previous work, in which strings were modeled as
idealized one-dimensional objects, we evolve the simplest example of an
underlying field theory containing local U(1) strings, the Abelian Higgs model.
Limitations imposed by finite computational volumes are overcome using the
scaling property of string networks and a further extrapolation related to the
lessening of the string width in comoving coordinates. The strings and their
decay products, which are automatically included in the field theory approach,
source metric perturbations via their energy-momentum tensor, the unequal-time
correlation functions of which are used as input into the CMB calculation
phase. These calculations involve the use of a modified version of CMBEASY,
with results provided over the full range of relevant scales. We find that the
string tension required to normalize to the WMAP 3-year data at multipole
is , where we have quoted statistical and systematic errors
separately, and is Newton's constant. This is a factor 2-3 higher than
values in current circulation.Comment: 23 pages, 14 figures; further optimized figures for 1Mb size limit,
appendix added before submission to journal, matches accepted versio
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