A Method for the Combination of Stochastic Time Varying Load Effects

The problem of evaluating the probability that a structure becomes unsafe under a combination of loads, over a given time period, is addressed. The loads and load effects are modeled as either pulse (static problem) processes with random occurrence time, intensity and a specified shape or intermittent continuous (dynamic problem) processes which are zero mean Gaussian processes superimposed 'on a pulse process. The load coincidence method is extended to problems with both nonlinear limit states and dynamic responses, including the case of correlated dynamic responses. The technique of linearization of a nonlinear limit state commonly used in a time-invariant problem is investigated for timevarying combination problems, with emphasis on selecting the linearization point. Results are compared with other methods, namely the method based on upcrossing rate, simpler combination rules such as Square Root of Sum of Squares and Turkstra's rule. Correlated effects among dynamic loads are examined to see how results differ from correlated static loads and to demonstrate which types of load dependencies are most important, i.e., affect' the exceedance probabilities the most. Application of the load coincidence method to code development is briefly discussed.National Science Foundation Grants CME 79-18053 and CEE 82-0759

Seismic Risk Evaluation of R.C. Buildings in Japan Designated in Accordance with the 1990 AIJ Guidelines

National Science Foundation Grant BCS 91-06390Kajima Foundatio

Flow Investigation on the Directional Instability of Aircraft with the Single Vertical Tail

AbstractAgeneric aircraft with the single vertical tail usually lose its directional stability at medium angle of attack (typically 20° to 30°). A model with moderate sweptwing of 47.5° and a conventional vertical tail is investigated in order to identify physical mechanisms responsible for directional stability. The results show that vertical tail and fuselage are the main components of the aircraft that generate yawing momentby the tests of model parts mounted and dismounted. The broken down vortex at windward side of vertical tail is the main reason for reducingstable yawing moment of vertical tail. Moreover, the middle part of the fuselage including air inlet and forepart of the wing is the main region of the fuselageenhancing unstable yawing moment

Fractionalization, topological order, and cuprate superconductivity

This paper is concerned with the idea that the electron is fractionalized in the cuprate high-$T_c$ materials. We show how the notion of topological order may be used to develop a precise theoretical characterization of a fractionalized phase in spatial dimension higher than one. Apart from the fractional particles into which the electron breaks apart, there are non-trivial gapped topological excitations - dubbed "visons". A cylindrical sample that is fractionalized exhibits two disconnected topological sectors depending on whether a vison is trapped in the "hole" or not. Indeed, "vison expulsion" is to fractionalization what the Meissner effect ("flux expulsion") is to superconductivity. This understanding enables us to address a number of conceptual issues that need to be confronted by any theory of the cuprates based on fractionalization ideas. We argue that whether or not the electron fractionalizes in the cuprates is a sharp and well-posed question with a definite answer. We elaborate on our recent proposal for an experiment to unambiguously settle this issue.Comment: 18 pages, 7 figure

Effect of Vortex Generator on Lateral and Directional Aerodynamic Characteristics at Medium Angle of Attack

AbstractA numerical computational investigation of applying vortex generator to conventional figuration aircraft for directional stability improvement at medium angle of attack was conducted in this article.Results showed that vortex generator can put off the critical angle of directional instability from 22°to 29°, in addition, vortex generator also had a very little influence on the lateral aerodynamic characteristic. The flowfield was simulated under the condition of 4° angle of sideslip, Mach number of 0.0882, and Reynolds number of 0.466 million

Ultra-short, repetitively pulsed atmospheric-pressure microplasmas

Low‐temperature atmospheric‐pressure plasmas are of great importance in many emerging biomedical and materials processing applications; in recent years there has been a growing interest in short‐pulsed excitation of such plasmas as a gateway to access highly non‐equilibrium discharge chemistry. This contribution employs time‐resolved electrical and optical diagnostics in combination with a time‐hybrid computational model to uncover the physics behind repetitive short pulsed excitation of atmospheric pressure plasma. It is shown that during the applied voltage pulse the peak dissipated power can exceed 1GW/cm3 resulting in electron densities approaching 1017 cm‐3 (~6 orders of magnitude larger than conventional low‐temperature atmospheric discharges) while the gas temperature remains close to room temperature

Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artificial and historic records

A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 design spectrum to a parametrically defined evolutionary power spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals’ response spectra with the GB 50011-2001 design spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice

Cerebral white matter hyperintensity volumes: normative age- and sex-specific values from 15 population-based cohorts comprising 14,876 individuals

White matter hyperintensities (WMH) increase with age, with marked interindividual variation. There is a need for normative data by age and sex, to improve individualized WMH burden assessment. In this study, we pooled cross-sectional data from 15 population-based cohorts (14,876 nondemented individuals, age 18–97 years), through the Meta VCI Map consortium. Whole brain and tract-specific MRI-assessed WMH volumes were calculated in MNI-152 space. We used quantile regression to create centile curves of WMH volume versus age, stratified by sex. Total WMH volume and interindividual variance increased exponentially with age for both sexes, with females showing higher WMH volumes. WMH volume increase with aging was not uniform across the white matter, but instead followed one of three different patterns depending on location. Age- and sex-specific normative data for total and regional WMH volumes were created. Our study provides detailed information on the normal distribution of total and regional WMH volumes across adulthood. The normative data enable a quantitative approach to interpreting total and regional WMH volumes in clinical practice and research settings.</p