RFID技术在博物馆观众行为研究中的应用

基于博物馆了解观众参观行为的重要性,利用RFID技术具有侦测、记录人员与对象流动信息的特性,开展了RFID技术在博物馆观众行为研究中的应用,并以秦陵博物院《丽山园遗珍——秦始皇陵出土文物精华展》为对象开展了应用实践,对RFID技术应用于观众行为研究的可行性和应用模式进行了探讨。结果表明,RFID技术应用于博物馆观众研究工作是可行的,是博物馆观众研究的又一有力工具,同时具有数据采集的便捷性、准确性、可靠性的优势。     

The winter anomaly as seen in the propagation of low frequency 40 kHz radio waves

An analysis of propagation data for LF 40 kHz radio waves shows that the field strength of the sky wave is enhanced during day-time on winter anomaly days (WAD), in striking contrast to the severe attenuation of HF radio waves. This peculiar enhancement of the field strength may be ascribed to an increase in the reflection coefficient. The analysis also demonstrates that the reflection height is lower on WAD, which seems to be associated with enhancements of ionization in the D-region. Moreover, it was found that WAD are characterized by an earlier occurrence in the morning and a delayed occurrence in the evening of pronounced interference maxima and minima, respectively.     

Direction of arrival of radio waves reflected from the E-region

A simple system for measuring the direction of arrival of continuous high frequency radio waves reflected obliquely from the ionosphere is described. Results obtained over a near vertical path are used to evaluate changes in the electron density gradients (tilts) in the E-region. Wave interference on the transmission due to multiple hop or ground wave propagation is discussed.     

Angular characteristics of radio pulses reflected from the subpolar ionosphere

This paper presents the results derived by measuring angular spectra of HF-radio pulses reflected from the subpolar ionospheric F2-region (62°N) using vertical-incidence soundings and a phase direction finder with Doppler filtering. The results correspond to three main types. One is the classical mirror reflection from the undisturbed ionospheric F2-region, typical of mid-latitudes (deviations from zenith do not exceed 3°; the angular spectrum width is less than 1°). The second type includes oblique diffuse reflections with a deviation from zenith of from 10 to 45°. The azimuth of arrival of these reflections is distributed in the range from 0 to 360°, the angular spectrum width is from 5 to 10°, and the range varies from 400 to 600 km. The third type includes anomalous mirror reflections with small deviations from zenith (not greater than 3°) but with substantially larger detection ranges (for example, 500km) as compared with the main reflections (250–300 km).     

The angular distribution of radio waves partially reflected from the lower ionosphere

Measurements of radio waves partially reflected from the D-region made using two antennae of very different beamwidth are reported. The arrays are composed of 40 and 4 dipoles respectively. It is shown that the gain of the larger array over the smaller is often variable—both in height and time. These results can be used to estimate the off-vertical angles from which significant energy is returned. For altitudes less than 80 km angles less than 10° seem to be usual but at higher altitudes the angles increase to values of the order of 15°–20°. Other important properties of the echoes, such as the probability distribution of the amplitude were also measured. The results are discussed with particular reference to the differential absorption method of measuring electron densities and also to the nature of the irregularities responsible for the partial reflections.     

A scintillation theory of the fading of HF waves returned from the F-region: receiver near transmitter

Scintillation theory is used to study the fading of HF radio waves returned from the ionospheric F-region to a receiver close to the transmitter. Estimates are made of

• 1.(i) the fluctuations of phase both for long term (∼ an hour) and for short term (∼ a fading correlation time),
• 2.(ii) the correlation distance,
• 3.(iii) the quasi-period of fading,
• 4.(iv) the angular divergence in the direction of arrival around the zenith and
• 5.(v) the correlation bandwidth.

The calculations are made as a function of wave frequency for two ionospheric penetration frequencies representative of high day-time values and low pre-sunrise values. Results are compared with observations of fading made with ionosondes over the past 40 years. Precise comparison is rendered impossible by omissions in the experimental data caused by lack of guidance from scintillation theory. Nevertheless, agreement is promising. When fading is deep but spread-F-region is not well-developed there is a slow modulation of the fading. This is what, for optical propagation in the troposphere, is called twinkling. The slow fluctuations observed by Bramley and Ross in the HF band constitute ionospheric twinkling. Calculated quasi-periods of twinkling range from about an hour down to about a couple of minutes, while calculated quasi-periods of fading range from about a couple of minutes down to about a tenth of a second.     

General formulae for absorption of radio waves in the ionosphere

The relationship between group path, phase path and absorption of radio waves is discussed and new approximations relating these quantities are presented. The new relationships include dependence on the angle between the wave normal and magnetic field directions and so, in contrast to other approximations they are not restricted to quasi-longitudinal or quasi-transverse situations. For deviative absorption it is found that the ordinary mode quasi-transverse approximation introduces errors of less than 5% except in the case of purely longitudinal propagation. For non-deviative absorption, use of the quasi-longitudinal approximation can introduce significant errors which particularly affect the determination of latitudinal variations in absorption.     

Iterative methods for treating the multiple scattering of radio waves

An iterative method is developed for treating multiple scattering in an extended random medium. The basis of the method is to use the single-scatter theory to derive a recurrence relation for the complex field. Since no restriction is placed on the incremental layer thickness, the single scatter theory can always be applied in this manner, subject only to the narrow-angle-scatter restriction. Indeed, in the differential limit of zero layer thickness, the recurrence relation, which is a difference equation, converges to the parabolic wave equation.The recurrence relation for the complex field is then used in conjunction with the Markov assumption to derive recurrence relations for the complex field moments of all orders. The recurrence relations for the general complex field moments converge to well known differential equations in the limit of zero layer thickness. The result is derived without constraints on the stastics of the index of refraction fluctuations. Moreover, the method of development suggests that the conditions for narrow-angle scattering alone are sufficient to guarantee the validity of the Markov approximation.Finally, a local phase-screen approximation is used to develop alternative recurrence relations for the complex field and the general complex field moments that are conceptually simpler and more efficient for numerical computation. Throughout the development, a formulation is used that retains an explicit dependence on the propagation angles relative to an arbituary but fixed co-ordinate system.     

Some Principles for the Reconstruction of Ancient Boat Structures

Several archaeological finds of ancient boats in Britain are currently being reconstructed using a variety of methods and standards. This paper discusses some of the general principles that should be observed so that such endeavours will be scholarly valuable. The Dover boat case study (later in this issue) is based on the analysis presented here. © 2006 The Authors     

谁对新四军皖南部队的严重损失负责

在震惊中外的皖南事变中,新四军皖南部队遭受严重损失.究其原因,主要是国民党顽固派的反共政策造成的.从共产党内来说,则与中共中央东南局书记、新四军主要领导人项英的错误有关;也与毛泽东对国民党顽固派的反共阴谋估计不足,对大局的判断失误有关.     

Methods and Challenges for the Seismic Assessment of Historic Masonry Structures

ABSTRACT

Despite the high vulnerability of historic structures to earthquakes, the approaches for evaluating seismic demand and capacity still appear inadequate and there is little consensus on the most appropriate assessment methods to use. To develop an improved knowledge on the seismic behavior of masonry structures and the reliability of analysis tools, two real-scale specimens were tested on a shake table, and several experts were invited to foresee failure mechanism and seismic capacity within a blind prediction test. Once unveiled, experimental results were simulated using multi-block dynamics, finite elements, or discrete elements. This article gathers the lessons learned and identifies issues requiring further attention. A combination of engineering judgment and numerical models may help to identify the collapse mechanism, which is as essential as it is challenging for the seismic assessment. To this purpose, discrete modeling approaches may lead to more reliable results than continuous ones. Even when the correct mechanism is identified, estimating the seismic capacity remains difficult, due to the complexity and randomness of the seismic response, and to the sensitivity of numerical tools to input variables. Simplified approaches based on rigid body dynamics, despite the considerable experience and engineering judgment required, provide as good results as do advanced simulations.     

Empirical Formulation for Estimating the Fundamental Frequency of Slender Masonry Structures

The fundamental frequency of a structure enables better assessment of its seismic demand for an efficient design and planning of its maintenance and retrofit strategy. The frequency is independent of the type of external loads, however, depends on structural stiffness, mass, damping and boundary conditions. In the case of slender masonry structures such as towers, minarets chimneys, and pagoda temples, it is influenced by mass and stiffness distribution, connection to adjacent structures, material properties, aspect ratio and slenderness ratio. In this present article, the data collected from various literature reviews on the slender masonry structures regarding dynamic, geometrical, and mechanical characteristics have been correlated to identify the major parameters influencing the fundamental frequency of such structures. The database has been used for developing an empirical formulation for predicting the fundamental frequency of such structures. The comparison between the experimental fundamental frequencies and the estimated fundamental frequencies are carried out in order to define reliability and accuracy of these empirical formulae.     

Protective Structures for the Preservation of Medieval Buildings and their Remains: Case Studies from Monastery Hilandar and Mount Athos

The objective of this study is to establish a methodology for temporary protective structures, that is, the guidelines for planning, design, and implementation of future protective structures. The basic method of this paper was the observation and analyses of temporary protective structures as well as the evaluation of the results achieved in implementation of these rules in completed structures, within the Hilandar Monastery complex on Mount Athos, in Greece. Mount Athos was inscribed on the UNESCO World Heritage List for its cultural and natural values. The Holy Mount Athos is a unique monastic complex in the world and only males are allowed past the entrance. Having performed the evaluation of certain types of temporary protective structures, the given results were offered as recommendation for their design and implementation. The most significant accomplishment of this paper is verification of the designed, calculated, and completed protective structures through practical application within the Hilandar Monastery complex, in accordance with all the factors of site management.     

Modelling Uncertainties of Italian Code-Conforming Structures for the Purpose of Seismic Response Analysis

ABSTRACT

This paper describes the multivariate statistical model of the structure-related modelling uncertainty, developed with reference to reinforced concrete, masonry, steel, and seismically isolated buildings, within the framework of the RINTC project. The model describes the variability of material properties as well as the uncertainty associated with the adopted response models. Specific aspects of each structural typology are also discussed, with a focus on the statistical dependence of the random variables in the model. Finally, the paper describes also the efficient sampling procedure adopted. Effect of model uncertainty on response for each typology are discussed in the corresponding papers within this special issue dedicated to the RINTC project.     

Rates for the job. Measures of disease frequency in palaeopathology

Measures of disease frequency are discussed and their use in palaeopathology illustrated with examples, both hypothetical and real. It is shown that prevalence rates are the appropriate rates to use when calculating the frequency of diseases in skeletal populations. The extent to which prevalence rates accurately reflect those in the living population from which the skeletons were derived is also considered and it is suggested that they are a reasonable approximation for diseases that do not shorten life span, but not for those that do. Finally, suggestions are made for dealing with missing data.     

A strange result in the measurement of the angles of arrival of the first and second echoes from the ionosphere at high radio frequencies

Angles of arrival of first echoes (those directly reflected from the ionosphere) and second echoes (those twice reflected from the ionosphere with an intermediate reflection from the ground) were measured. It is easy to show that under specified conditions the off-vertical angle of arrival of the second echo ought to be twice that of the first echo. It is consistently found to be less than this for much of the time. Several possibilities are canvassed, but none provide a convincing explanation. The place on the Earth from which the second echo was reflected was nearly always the sea or flat ground. Apparently, rapid phase variations, as the tilt of the ionosphere changed, prevented recognition of the second echo by this particular radar system for echoes reflected from rough terrain.     

A Microscale Approach for the Seismic Response of MDOF Structures Including Soil-Foundation-Structure Interaction

In this article, a three-dimensional microscale computational framework utilizing the discrete element method is presented to analyze the seismic response of soil-foundation- MDOF structure systems. The proposed approach is used to explore the response of MDOF structures on a square embedded footing founded on a dry granular deposit. Computational simulations were conducted to investigate the response of the system to several base excitations. The impact of replacing a MDOF structure with its equivalent single degree of freedom (ESDOF) structure while accounting for soil-foundation-structure interaction (SFSI) is investigated. Detrimental or beneficial effect of SFSI on the response is also examined.