37,080 research outputs found
Conditional Spectrum-Based Ground Motion Selection. Part II: Intensity-Based Assessments and Evaluation of Alternative Target Spectra
In a companion paper, an overview and problem definition was presented for ground motion selection on the basis of the conditional spectrum (CS), to perform risk-based assessments (which estimate the annual rate of exceeding a specified structural response amplitude) for a 20-story reinforced concrete frame structure. Here, the methodology is repeated for intensity-based assessments (which estimate structural response for ground motions with a specified intensity level) to determine the effect of conditioning period. Additionally, intensity-based and risk-based assessments are evaluated for two other possible target spectra, specifically the uniform hazard spectrum (UHS) and the conditional mean spectrum (CMS, without variability).It is demonstrated for the structure considered that the choice of conditioning period in the CS can substantially impact structural response estimates in an intensity-based assessment. When used for intensity-based assessments, the UHS typically results in equal or higher median estimates of structural response than the CS; the CMS results in similar median estimates of structural response compared with the CS but exhibits lower dispersion because of the omission of variability. The choice of target spectrum is then evaluated for risk-based assessments, showing that the UHS results in overestimation of structural response hazard, whereas the CMS results in underestimation. Additional analyses are completed for other structures to confirm the generality of the conclusions here. These findings have potentially important implications both for the intensity-based seismic assessments using the CS in future building codes and the risk-based seismic assessments typically used in performance-based earthquake engineering applications
Conditional Spectrum-Based Ground Motion Selection. Part I: Hazard Consistency for Risk-Based Assessments
The conditional spectrum (CS, with mean and variability) is a target response spectrum that links nonlinear dynamic analysis back to probabilistic seismic hazard analysis for ground motion selection. The CS is computed on the basis of a specified conditioning period, whereas structures under consideration may be sensitive to response spectral amplitudes at multiple periods of excitation. Questions remain regarding the appropriate choice of conditioning period when utilizing the CS as the target spectrum. This paper focuses on risk-based assessments, which estimate the annual rate of exceeding a specified structural response amplitude. Seismic hazard analysis, ground motion selection, and nonlinear dynamic analysis are performed, using the conditional spectra with varying conditioning periods, to assess the performance of a 20-story reinforced concrete frame structure. It is shown here that risk-based assessments are relatively insensitive to the choice of conditioning period when the ground motions are carefully selected to ensure hazard consistency. This observed insensitivity to the conditioning period comes from the fact that, when CS-based ground motion selection is used, the distributions of response spectra of the selected ground motions are consistent with the site ground motion hazard curves at all relevant periods; this consistency with the site hazard curves is independent of the conditioning period. The importance of an exact CS (which incorporates multiple causal earthquakes and ground motion prediction models) to achieve the appropriate spectral variability at periods away from the conditioning period is also highlighted. The findings of this paper are expected theoretically but have not been empirically demonstrated previously
Fast-neutron spectrometer developments
Li6 sandwich-type neutron spectrometer is equipped with proportional counter for particle identification. System uses current-sensitive preamplifiers to minimize pile-up of gamma-ray and particle pulses
Quasi-equilibrium binary black hole sequences for puncture data derived from helical Killing vector conditions
We construct a sequence of binary black hole puncture data derived under the
assumptions (i) that the ADM mass of each puncture as measured in the
asymptotically flat space at the puncture stays constant along the sequence,
and (ii) that the orbits along the sequence are quasi-circular in the sense
that several necessary conditions for the existence of a helical Killing vector
are satisfied. These conditions are equality of ADM and Komar mass at infinity
and equality of the ADM and a rescaled Komar mass at each puncture. In this
paper we explicitly give results for the case of an equal mass black hole
binary without spin, but our approach can also be applied in the general case.
We find that up to numerical accuracy the apparent horizon mass also remains
constant along the sequence and that the prediction for the innermost stable
circular orbit is similar to what has been found with the effective potential
method.Comment: 6 pages, 3 figures, 1 tabl
Assembly and analysis of fragmentation data for liquid propellant vessels
Fragmentation data was assembled and analyzed for exploding liquid propellant vessels. These data were to be retrieved from reports of tests and accidents, including measurements or estimates of blast yield, etc. A significant amount of data was retrieved from a series of tests conducted for measurement of blast and fireball effects of liquid propellant explosions (Project PYRO), a few well-documented accident reports, and a series of tests to determine auto-ignition properties of mixing liquid propellants. The data were reduced and fitted to various statistical functions. Comparisons were made with methods of prediction for blast yield, initial fragment velocities, and fragment range. Reasonably good correlation was achieved. Methods presented in the report allow prediction of fragment patterns, given type and quantity of propellant, type of accident, and time of propellant mixing
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Seasonal predictability of the winter North Atlantic Oscillation from a jet stream perspective
The winter North Atlantic Oscillation (NAO) has varied on interannual and decadal
timescales over the last century, associated with variations in the speed and latitude of the eddy-driven jet
stream. This paper uses hindcasts from two operational seasonal forecast systems (the European Centre for
Medium-range Weather Forecasts's seasonal forecast system, and the U.K. Met Office global seasonal
forecast system) and a century-long atmosphere-only experiment (using the European Centre for
Medium-range Weather Forecasts's Integrated Forecasting System model) to relate seasonal prediction
skill in the NAO to these aspects of jet variability. This shows that the NAO skill realized so far arises from
interannual variations in the jet, largely associated with its latitude rather than speed. There likely remains
further potential for predictability on longer, decadal timescales. In the small sample of models analyzed
here, improved representation of the structure of jet variability does not translate to enhanced seasonal
forecast skill
Classification of the Streptococcus Lactis group
\u27l\u27he lactic acid producing streptococci show certain differences, some of which must be of importance from the standpoint of the growth of these organisms in dairy products. A classification of this group of organisms has been proposed; it is not presumed to be complete and other types will necessarily be added. The classification is as follows:
Typical S. lactis
Malty S. Iactis—S. lactis var. maltigenes
Ropy S. lactis—S. lactis var. hollandicus
Slow reducing S. lactis—S. lactis var. anoxyphilus
Slow coagulating S. lactis—S. lactis var. tardus
Heat resistant lactic acid streptococci—S. thermophilu
Influence of the milk on the starter made from it
Altho the types of bacteria present is a very important consideration in the preparation of starters, the medium in which the organisms are to grow is also important. Normal milk, either whole or skimmed, is apparently the most satisfactory material as well as the most widely used. Milk reconstituted from mill} powder or condensed milk, and normal milk handled in various Ways by diluting and adding such fermentable substances as lactose and glucose have been employed for the making of starters\ but have not come into general usE and do not seem to yield as desirable a product as normal milk
Studies on starters
For a number of years the dairy section of the Iowa Agricultural Experiment Station has devoted considerable effort to an investigation of starters. This has seemed advisable because good starters have been shown to be very helpful in improving the quality of butter, which is the important dairy product of the state
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