Phase information and the evolution of cosmological density perturbations     

Lung-Yih Chiang  Peter Coles 《Monthly notices of the Royal Astronomical Society》2000,311(4):809-824

The Fourier transform of cosmological density perturbations can be represented in terms of amplitudes and phases for each Fourier mode. We investigate the phase evolution of these modes using a mixture of analytical and numerical techniques. Using a toy model of one-dimensional perturbations evolving under the Zel'dovich approximation as an initial motivation, we develop a statistic that quantifies the information content of the distribution of phases. Using numerical simulations beginning with more realistic Gaussian random-phase initial conditions, we show that the information content of the phases grows from zero in the initial conditions, first slowly and then rapidly when structures become non-linear. This growth of phase information can be expressed in terms of an effective entropy. Gaussian initial conditions are a maximum entropy realization of the initial power spectrum; gravitational evolution decreases the phase entropy. We show that our definition of phase entropy results in a statistic that explicitly quantifies the information stored in the phases of density perturbations (rather than their amplitudes), and that this statistic displays interesting scaling behaviour for self-similar initial conditions.  相似文献   

Real‐time river bed scour monitoring and synchronous maximum depth data collected during Typhoon Soulik in 2013          下载免费PDF全文

Han‐Chung Yang  Chih‐Chiang Su 《水文研究》2015,29(6):1056-1068

A critical concern regarding river bed stabilization and river engineering is the short‐term general scour that occurs in a field setting far from a river‐crossing structure or embankment during a typhoon‐induced flood. This study investigated the improvement of existing techniques that have been used to measure river bed scour. One of these techniques is the numbered‐brick column or scour chains method, in which only the maximum general scour depth of river bed is observed. A wireless tracer for monitoring real‐time scour was set‐up with a numbered‐brick column and was employed to collect synchronous data. The proposed method was successfully used to observe both real‐time scour and the maximum depth at flood peak. This observation was conducted at a steep gravel‐bed reach of the Shuideliaw Embankment on the intermittent Choshui River in Central Taiwan during Typhoon Soulik, which occurred in 2013. Future studies must be conducted to complete the development of an automatic real‐time scour and flood monitoring system for use in severe weather and flow conditions; this would facilitate the identification of river bed scour during conditions of unstable flow and the improvement of flood prevention engineering, bridge closure detection and emergency evacuation procedures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Spatial variability and mechanisms underlying El Niño-induced droughts in Mexico     

Tripti Bhattacharya  John C. H. Chiang 《Climate Dynamics》2014,43(12):3309-3326

The El Niño Southern Oscillation plays a key role in modulating interannual rainfall variability in Mexico. While El Niño events are linked to drought in Mexico, uncertainty exists about the spatial pattern and causal mechanisms behind El Niño-induced drought. We use lead/lag correlation analysis of rainfall station data to identify the spatial pattern of drought associated with the summer before, and the spring following, the peak of warm SST anomalies in the eastern equatorial Pacific. We also use atmospheric fields from the North American Regional Reanalysis to calculate the anomalous moisture budget and diagnose the mechanisms associated with El Niño-induced drought in Mexico. We find that reduced rainfall occurs in Mexico in both the summer before and the spring after a peak El Niño event, especially in regions of climatologically strong convection. The teleconnection in the developing phase of El Niño is primarily driven by changes in subsidence resulting from anomalous convection in the equatorial Pacific. The causes of drought during the decaying phase of El Niño events are varied: in some years, descent anomalies dominate other moisture budget terms, while in other years, drying of the boundary layer on the Mexican plateau is important. We suggest that the latter may result from the interaction of weakened southeasterly winds in the Intra-Americas Sea with high topography along the Atlantic coast of Mexico. Weakened winds are likely driven by a reduced sea level pressure gradient between the Atlantic and the Pacific. Changes in easterly wave activity may contribute to drought in the developing phase of El Niño, but may be less important in the decaying phase of El Niño.  相似文献   

A new coarse-time GPS positioning algorithm using combined Doppler and code-phase measurements   总被引：2，自引：2，他引：0  

Hung-Wei Chen  He-Sheng Wang  Yi-Te Chiang  Fan-Ren Chang 《GPS Solutions》2014,18(4):541-551

A new coarse-time Global Positioning System (GPS) positioning algorithm based on the use of Doppler and code-phase measurements is proposed and described. The proposed method was demonstrated to be essential for reducing the time to first fix and the power consumption in a GPS receiver. Only 1 ms of data is required to obtain a positioning fix with accuracy comparable to that of the traditional GPS navigation algorithm. The algorithm is divided into two parts. In the first part, the Doppler measurement of the GPS signal is used to determine the coarse user position. With proper constraints, the required time accuracy for the Doppler measurements can be relaxed to be as long as 12 h. In the second part of the algorithm, the accurate user position is calculated by means of the 1 ms code-phase data. The traditional tracking process is no longer necessary in the proposed algorithm. Using the acquired 1-ms code-phase measurement, the positioning accuracy was determined to be approximately a few tens of meters in our experimental results. However, if the data length is extended to 10 ms, the positioning accuracy can be improved to within 10–20 m, which is similar to that of the traditional GPS positioning method. Various experiments were conducted to verify the usefulness of the proposed algorithm.  相似文献   

An 1800-yr record of decadal-scale hydroclimatic variability in the upper Arkansas River basin from bristlecone pine     

Connie A. Woodhouse  Gregory T. Pederson  Stephen T. Gray   《Quaternary Research》2011,75(3):483-490

Bristlecone pine trees are exceptionally long-lived, and with the incorporation of remnant material have been used to construct multi-millennial length ring–width chronologies. These chronologies can provide valuable information about past temperature and moisture variability. In this study, we outline a method to build a moisture-sensitive bristlecone chronology and assess the robustness and consistency of this sensitivity over the past 1200 yr using new reconstructions of Arkansas River flow (AD 1275–2002 and 1577–2002) and the summer Palmer Drought Sensitivity Index. The chronology, a composite built from parts of three collections in the central Rocky Mountains, is a proxy for decadal-scale moisture variability for the past 18 centuries. Since the sample size is small in some portions of the time series, the chronology should be considered preliminary; the timing and duration of drought events are likely the most robust characteristics. This chronology suggests that the region experienced increased aridity during the medieval period, as did much of western North America, but that the timing and duration of drought episodes within this period were somewhat different from those in other western locations, such as the upper Colorado River basin.  相似文献   

Global energy budget changes to high latitude North Atlantic cooling and the tropical ITCZ response     

Ivana Cvijanovic  John C. H. Chiang 《Climate Dynamics》2013,40(5-6):1435-1452

The intertropical convergence zone (ITCZ) in atmospheric general circulation models (coupled to slab ocean) shift southwards in response to northern extratropical cooling. Previous studies have demonstrated the utility of diagnosing the atmospheric energy fluxes in interpreting this teleconnection. This study investigates the nature of global energy flux changes in response to North Atlantic high latitude cooling applied to the Community Atmosphere Model version 3 coupled to a slab ocean, focusing on key local and remote feedbacks that collectively act to alter the energy budget and atmospheric energy transport. We also investigate the relative roles of tropical sea surface temperature (SST) and energy flux changes in the ITCZ response to North Atlantic cooling. Using a radiative kernel technique, we quantify the effects of key feedbacks—temperature, cloud and water vapor, to the top-of-the-atmosphere radiative flux changes. The results show only partial local energy flux compensation to the initial perturbation in the high latitudes, originating from the negative temperature feedback and opposed by positive shortwave albedo and longwave water vapor feedbacks. Thus, an increase in the atmospheric energy transport to the Northern extratropics is required to close the energy budget. The additional energy flux providing this increase comes from top-of-the-atmosphere radiative flux increase over the southern tropics, primarily from cloud, temperature and longwave water vapor feedbacks, and largely as a consequence of increased deep convection. It has been previously argued that the role of tropical SST changes was secondary to the role played by the atmospheric energy flux requirements in controlling the ITCZ shifts, proposing that the SST response is a result of the surface energy budget and not a driver of the precipitation response. Using a set of idealized simulations with the fixed tropical SSTs, we demonstrate that the ITCZ shifts are not possible without the tropical SST changes and suggest that the tropical SSTs are a more suitable driver of tropical precipitation shifts compared to the atmospheric energy fluxes. In our simulations, the ITCZ shifts are influenced mainly by the local (tropical) SST forcing, apparently independent of the actual high latitude energy demand.  相似文献   

A probabilistic approach for earthquake risk assessment based on an engineering insurance portfolio     

Wen-Ko Hsu  Wei-Ling Chiang  Qiang Xue  Dung-Mou Hung  Pei-Chun Huang  Cheng-Wu Chen  Chung-Hung Tsai 《Natural Hazards》2013,65(3):1559-1571

This paper presents the construction classification of the existing engineering covers in Taiwan. The exposure profile and variable vulnerability during different construction phases are established for some kinds of classes of construction. Finally, we present a method and framework to estimate the probable maximum loss of engineering insurance portfolio during an earthquake with consideration of the dynamic nature of structural changes and exposure values during a construction project.  相似文献   

Simultaneous measurement of humidity and temperature in the lower troposphere over Chung-Li,Taiwan     

Chih-Wei Chiang  Subrata Kumar Das  Jan-Bai Nee  Shun-xing Hu  Huan-ling Hu 《Journal of Atmospheric and Solar》2009,71(12):1389-1396

A combined Raman–Rayleigh lidar has been designed at Chung-Li, Taiwan for the simultaneous measurement of water-vapor mixing ratio, temperature and extinction-to-backscatter ratio of aerosol in the lower troposphere. The technique of Raman–Rayleigh lidar can retrieve correct temperature profile in the lower troposphere where the measurements are underestimated due to the aerosol loading. Two typical cases are discussed under different humidity (dry/wet) conditions. The water vapor and temperature profile have shown a good agreement with radiosonde. Simultaneous measurement of Raman–Rayleigh lidar also illustrates the physical nature of the aerosol and is useful in understanding the effects of humidity on aerosol swelling.  相似文献   

Arctic microbial ecosystems and impacts of extreme warming during the International Polar Year     

Warwick F. Vincent  Lyle G. Whyte  Connie Lovejoy  Charles W. Greer  Isabelle Laurion  Curtis A. Suttle  Jacques Corbeil  Derek R. Mueller 《Polar Science》2009,3(3):171-180

As a contribution to the International Polar Year program MERGE (Microbiological and Ecological Responses to Global Environmental change in polar regions), studies were conducted on the terrestrial and aquatic microbial ecosystems of northern Canada (details at: http://www.cen.ulaval.ca/merge/). The habitats included permafrost soils, saline coldwater springs, supraglacial lakes on ice shelves, epishelf lakes in fjords, deep meromictic lakes, and shallow lakes, ponds and streams. Microbiological samples from each habitat were analysed by HPLC pigment assays, light and fluorescence microscopy, and DNA sequencing. The results show a remarkably diverse microflora of viruses, Archaea (including ammonium oxidisers and methanotrophs), Bacteria (including filamentous sulfur-oxidisers in a saline spring and benthic mats of Cyanobacteria in many waterbodies), and protists (including microbial eukaryotes in snowbanks and ciliates in ice-dammed lakes). In summer 2008, we recorded extreme warming at Ward Hunt Island and vicinity, the northern limit of the Canadian high Arctic, with air temperatures up to 20.5 °C. This was accompanied by pronounced changes in microbial habitats: deepening of the permafrost active layer; loss of perennial lake ice and sea ice; loss of ice-dammed freshwater lakes; and 23% loss of total ice shelf area, including complete break-up and loss of the Markham Ice Shelf cryo-ecosystem. These observations underscore the vulnerability of Arctic microbial ecosystems to ongoing climate change.  相似文献   

Equivalent series system to model a multiple friction pendulum system with numerous sliding interfaces for seismic analyses     

C. S. Tsai  H. C. Su  T. C. Chiang 《地震工程与工程振动(英文版)》2014,13(1):85-99

Current structural analysis software programs offer few if any applicable device-specifi c hysteresis rules or nonlinear elements to simulate the precise mechanical behavior of a multiple friction pendulum system(MFPS) with numerous sliding interfaces.Based on the concept of subsystems,an equivalent series system that adopts existing nonlinear elements with parameters systematically calculated and mathematically proven through rigorous derivations is proposed.The aim is to simulate the characteristics of sliding motions for an MFPS isolation system with numerous concave sliding interfaces without prior knowledge of detailed information on the mobilized forces at various sliding stages.An MFPS with numerous concave sliding interfaces and one articulated or rigid slider located between these interfaces is divided into two subsystems: the fi rst represents the concave sliding interfaces above the slider,and the second represents those below the slider.The equivalent series system for the entire system is then obtained by connecting those for each subsystem in series.The equivalent series system is validated by comparing numerical results for an MFPS with four sliding interfaces obtained from the proposed method with those from a previous study by Fenz and Constantinou.Furthermore,these numerical results demonstrate that an MFPS isolator with numerous concave sliding interfaces,which may have any number of sliding interfaces,is a good isolation device to protect structures from earthquake damage through appropriate designs with controllable mechanisms.  相似文献