2,387 research outputs found
The procurement and evaluation of a prototype laser satellite-tracking system Final report, 1 Jan. 1967 - 30 Sep. 1968
Pulsed ruby laser satellite tracking syste
Principles of moment distribution applied to stability of structures composed of bars or plates
The principles of the cross method of moment distribution, which have previously been applied to the stability of structures composed of bars under axial load, are applied to the stability of structures composed of long plates under longitudinal load. A brief theoretical treatment of the subject, as applied to structures composed of either bars or plates, is included, together with an illustrative example for each of these two types of structure. An appendix presents the derivation of the formulas for the various stiffnesses and carry-over factors used in solving problems in the stability of structures composed of long plates
Principles of moment distribution applied to stability of structures composed of bars or plates
Principles of the cross method of moment distribution, which have previously been applied to the stability of structures composed of bars under axial load, are applied to the stability of structures composed of long plates under longitudinal load
Column and Plate Compressive Strengths of Aircraft Structural Materials: 24S-T Aluminum-alloy Sheet
Constraints on the Heating of High Temperature Active Region Loops: Observations from Hinode and SDO
We present observations of high temperature emission in the core of a solar
active region using instruments on Hinode and SDO. These multi-instrument
observations allow us to determine the distribution of plasma temperatures and
follow the evolution of emission at different temperatures. We find that at the
apex of the high temperature loops the emission measure distribution is
strongly peaked near 4 MK and falls off sharply at both higher and lower
temperatures. Perhaps most significantly, the emission measure at 0.5 MK is
reduced by more than two orders of magnitude from the peak at 4 MK. We also
find that the temporal evolution in broad-band soft X-ray images is relatively
constant over about 6 hours of observing. Observations in the cooler SDO/AIA
bandpasses generally do not show cooling loops in the core of the active
region, consistent with the steady emission observed at high temperatures.
These observations suggest that the high temperature loops observed in the core
of an active region are close to equilibrium. We find that it is possible to
reproduce the relative intensities of high temperature emission lines with a
simple, high-frequency heating scenario where heating events occur on time
scales much less than a cooling time. In contrast, low-frequency heating
scenarios, which are commonly invoked to describe nanoflare models of coronal
heating, do not reproduce the relative intensities of high temperature emission
lines and predict low-temperature emission that is approximately an order of
magnitude too large. We also present an initial look at images from the SDO/AIA
94 A channel, which is sensitive to Fe XVIII.Comment: Movies are available at
http://tcrb.nrl.navy.mil/~hwarren/temp/papers/active_region_core/ Paper has
been refereed and revise
Second harmonic generation in SiC polytypes
LMTO calculations are presented for the frequency dependent second harmonic
generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All
independent tensor components are calculated. The spectral features and the
ratios of the 333 to 311 tensorial components are studied as a function of the
degree of hexagonality. The relationship to the linear optical response and the
underlying band structure are investigated. SHG is suggested to be a sensitive
tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure
Physical IC debug ─ backside approach and nanoscale challenge
Physical analysis for IC functionality in submicron technologies requires access through chip backside. Based upon typical global backside preparation with 50–100 µm moderate silicon thickness remaining, a state of the art of the analysis techniques available for this purpose is presented and evaluated for functional analysis and layout pattern resolution potential. A circuit edit technique valid for nano technology ICs, is also presented that is based upon the formation of local trenches using the bottom of Shallow Trench Isolation (STI) as endpoint for Focused Ion Beam (FIB) milling. As a derivative from this process, a locally ultra thin silicon device can be processed, creating a back surface as work bench for breakthrough applications of nanoscale analysis techniques to a fully functional circuit through chip backside. Several applications demonstrate the power and potential of this new approach
Association of APOE ɛ4 and Plasma p-tau181 with Preclinical Alzheimer's Disease and Longitudinal Change in Hippocampus Function
BACKGROUND: The Apolipoprotein E (APOE) ɛ4 allele has been linked to increased tau phosphorylation and tangle formation. APOE ɛ4 carriers with elevated tau might be at the higher risk for AD progression. Previous studies showed that tau pathology begins early in areas of the medial temporal lobe. Similarly, APOE ɛ4 carriers showed altered hippocampal functional integrity. However, it remains unknown whether elevated tau accumulation on hippocampal functional changes would be more pronounced for APOE ɛ4 carriers. OBJECTIVE: We related ɛ4 carriage to levels of plasma phosphorylated tau (p-tau181) up to 15 years prior to AD onset. Furthermore, elevated p-tau181 was explored in relation to longitudinal changes in hippocampal function and connectivity. METHODS: Longitudinal population-based study. Plasma p-tau181 was analyzed in 142 clinically defined Alzheimer's disease (AD) cases and 126 controls. The longitudinal analysis involved 87 non-demented individuals with two waves of plasma samples and three waves of functional magnetic resonance imaging during rest and memory encoding. RESULTS: Increased p-tau181 was observed for both ɛ4 carriers and non-carriers close to AD, but exclusively for ɛ4 carriers in the early preclinical groups (7- and 13-years pre-AD). In ɛ4 carriers, longitudinal p-tau181 increase was paralleled by elevated local hippocampal connectivity at rest and subsequent reduction of hippocampus encoding-related activity. CONCLUSION: Our findings support an association of APOE ɛ4 and p-tau181 with preclinical AD and hippocampus functioning
Evidence for Steady Heating: Observations of an Active Region Core with Hinode and TRACE
Previous observations have not been able to exclude the possibility that high
temperature active region loops are actually composed of many small scale
threads that are in various stages of heating and cooling and only appear to be
in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS)
and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate
the properties of high temperature coronal plasma in extraordinary detail. We
examine the emission in the core of an active region and find three independent
lines of evidence for steady heating. We find that the emission observed in XRT
is generally steady for hours, with a fluctuation level of approximately 15% in
an individual pixel. Short-lived impulsive heating events are observed, but
they appear to be unrelated to the steady emission that dominates the active
region. Furthermore, we find no evidence for warm emission that is spatially
correlated with the hot emission, as would be expected if the high temperature
loops are the result of impulsive heating. Finally, we also find that
intensities in the "moss", the footpoints of high temperature loops, are
consistent with steady heating models provided that we account for the local
expansion of the loop from the base of the transition region to the corona. In
combination, these results provide strong evidence that the heating in the core
of an active region is effectively steady, that is, the time between heating
events is short relative to the relevant radiative and conductive cooling
times.Comment: Minor changes based on the final report from the referee; Movies are
available from the first autho
National Geodetic Satellite Program, Part II: Smithsonian Astrophysical Observatory
A sequence of advances in the determination of geodetic parameters presented by the Smithsonian Astrophysical Observatory are described. A Baker-Nunn photographic system was used in addition to a ruby-laser ranging system to obtain data for refinement of geodetic parameters. A summary of the data employed to: (1) derive coordinates for the locations of various tracking stations; and (2) determine the gravitational potential of the earth, is presented
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