Frequency dependent polarization analysis of ambient seismic noise recorded at a broadband seismometer in the central United States

We present a new approach to polarization analysis of seismic noise recorded by three-component seismometers. It is based on statistical analysis of frequency-dependent particle motion properties determined from a large number of time windows via eigenanalysis of the 3-by-3, Hermitian, spectral covariance matrix. We applied the algorithm to continuous data recorded in 2009 by the seismic station SLM, located in central North America. A rich variety of noise sources was observed. At low frequencies （〈0.05 Hz） we observed a tilt-related signal that showed some elliptical motion in the horizontal plane. In the microseism band of 0.05-0.25 Hz, we observed Rayleigh energy arriving from the northeast, but with three distinct peaks instead of the classic single and double frequency peaks. At intermediate frequencies of 0.5-2.0 Hz, the noise was dominated by non-fundamental-mode Rayleigh energy, most likely P and Lg waves. At the highest frequencies （〉3 Hz）, Rayleigh-type energy was again dominant in the form of Rg waves created by nearby cultural activities. Analysis of the time dependence of noise power shows that a frequency range of at least 0.02-1.0 Hz （much larger than the microseism band） is sensitive to annual, meteorologically induced sources of noise.

Design of broad angular phase retarders for the complete polarization analysis of extreme ultraviolet radiation

A method of designing broad angular phase retarders in the extreme ultraviolet （EUV） region is presented. The design is based on a standard Levenberg-Marquardt algorithm combined with a common merit function. Using this method, a series of broad angular EUV phase retarders were designed using aperiodic Mo/Si multilayers. At photon energy of 90 eV, broad angular phase retarders with 30°, 60°, and 90° phase retardations have been realized in the angular range of 39°-51°. By analyzing and comparing the performances of the designed broad angular phase retarders, we found that the Mo/Si multilayer with more layers could obtain higher phase retardation in broader angular range when used to design the broad angular phase retarder. Broad angular phase retarders possess lower sensitivity toward changing incident angle compared with the traditional phase retarders designed with transmission periodic multilayers, and can be used for the polarization control of broad angular EUV sources.

Application of the time-frequency polarization analysis to study the complexity of surface wave propagation

new technique called the timefrequency polarization analysis was introduced in this paper. The technique combined the traditional surface wave analysis techniques (moving window and multifilter) with the singular value decomposition method to measure the incidence azimuth of surface waves with different wavelengths. It was applied to study the propagation paths of surface waves across the different blocks of Chinese continent and different zones of QinghaiXizang (Tibet) plateau. The results show that the method can make full use of the differences in frequency compositions and arrival times of different surface wave modes, and give better polarization analysis results. The analysis by actual data shows that the lateral heterogeneity of the lithospheric structure influences the propagation paths of surface waves severely. Deviations of the paths across the QinghaiXizang plateau from great circle paths are great. Deviations of the surface waves across the different zones in QinghaiXizang plateau are different.

High-Temperature Performance Analysis of AlGaN/GaN Polarization Doped Field Effect Transistors Based on the Quasi-Multi-Channel Model

We report on the temperature-dependent dc performance of A1GaN/GaN polarization doped field effect transistors （PolFETs）. The rough decrements of drain current and transeonductance with the operation temperature are observed. Compared with the conventional HFETs, the drain current drop of the PolFET is smaller. The transeonductance drop of PolFETs at different gate biases shows different temperature dependences. From the aspect of the unique carrier behaviors of graded AlGaN/GaN heterostructure, we propose a quasi-multi-channel model to investigate the physics behind the temperature-dependent performance of AlGaN/GaN PolFETs.

Dynamic impact properties of deep sandstone under thermal-hydraulicmechanical coupling loads

The deep rock mass within coal mines situated in a challenging environment are characterized by high ground stress,high geotemperature,high osmotic water pressure,and dynamic disturbances from mechanical excavation.To investigate the impact of this complex mechanical environment on the dynamic characteristics of roof sandstone in self-formed roadways without coal pillars,standard specimens of deep sandstone from the 2611 upper tunnel working face of the Yongmei Company within the Henan Coal Chemical Industry Group in Henan,China were prepared,and an orthogonal test was designed.Using a self-developed geotechnical dynamic impact mechanics test system,triaxial dynamic impact tests under thermal-hydraulicmechanical coupling conditions were conducted on deep sandstone.The results indicate that under high confining pressure,deep sandstone exhibits pronounced brittle failure at low temperatures,with peak strength gradually decreasing as temperature and osmotic water pressure increase.Conversely,under low confining pressure and low temperature,the brittleness of deep sandstone weakens gradually,while ductility increases.Moreover,sandstone demonstrates higher peak strength at low temperatures under high axial pressure conditions,lower peak strength at high temperatures,and greater strain under low axial pressure and high osmotic water pressure.Increases in impact air pressure and osmotic water pressure have proportionally greater effects on peak stress and peak strain.Approximately 50%of the input strain energy is utilized as effective energy driving the sandstone fracture process.Polar analysis identifies the optimal combination of factors affecting the peak stress and peak strain of sandstone.Under the coupling effect,intergranular and transgranular fractures occur within the sandstone.SEM images illustrate that the damage forms range from minor damage with multiple fissures to extensive fractures and severe fragmentation.This study elucidates the varied dynamic impact mechanical properties of deep sandstones under thermal-hydraulic-mechanical coupling,along with multifactor analysis methods and their optimal factor combinations.

Instantaneous polarization filtering focused on suppression of surface waves

The different characteristics of polarization of body and Rayleigh waves make it possible to separate these two types of waves by their characteristics and suppress the latter.The moving time-window analysis often is used in polarization filtering but it is difficult to determine a suitable time-window length,resulting in some problems,such as complex eigenvalues and non-convergence.For overcoming these disadvantages,in this paper,we introduce the concept of complex-trace analysis and conduct de-noise processing to suppress undesirable surface waves by instantaneous polarization analysis in the case of horizontal and vertical component seismic recordings from the Hauinan coal mine.The performance of the method is illustrated by examples with synthetic and field data and its effectiveness to remove surface waves from multi-component seismic data is demonstrated.

Detection of ULF electromagnetic emissions as a precursor to two earthquakes in China

The geomagnetic data recorded by Kashi and Jinghai observatories in China were analyzed with improved polarization method. We compared the result around 0.01 Hz which is thought to be useful to detect the ULF anomaly with the result around 0.1 Hz which was inferred from the earthquake depth according to the skin effect, and found that 0.1 Hz is more proper to detect the ULF anomaly for both earthquakes studied in this paper.

Developing time-of-flight polarized neutron capability at the China Spallation Neutron Source

Polarized neutrons play an indispensable role in neutron scattering research and have been incorporated into various neutron diffractometers and spectrometers. Recognizing the importance of polarized neutrons, the China Spallation Neutron Source(CSNS) has dedicated resources for developing its own capabilities for polarized neutron techniques. Hence, a polarized neutron development platform was allocated to the BL-20 beam port at CSNS for the purpose of facilitating new technological developments and calibration of instruments. Here, we report the progress we have made in terms of using the established development platform at BL-20, including the characterization of neutron spin filter cells manufactured at CSNS, the calibration of self-developed polarized neutron instruments, performance of the polarized neutron technique applied to beamlines,and associated simulation work for beamline magnetic field environments. These results demonstrate the capability of the CSNS to develop time-of-flight polarized neutron instruments and techniques in-house, which will be incorporated into the construction of CSNS neutron beamlines.

Locating the Source Regions of the Single and Double-Frequency Microseisms to Investigate the Source Effects on HVSR in Site Effect Analysis

Evaluating the seismic site effect by the ambient noise based horizontal-to-vertical spectral ratio(HVSR)method is strongly affected by the spatial and temporal variations of the ambient noise sources.Therefore,it is necessary to locate the source regions of ambient noise and investigate the relationships between the source energy and HVSR values at the predominant frequency(HVSRf_(0))of the site.The generation mechanisms of the single-and double-frequency microseisms(SFMs,0.05-0.085 Hz and DFMs,0.1-0.5 Hz)in ambient noise are better understood than the noise in other frequency bands and they are dominantly composed of fundamental Rayleigh(Rg)waves.With this advantage,the recordings of SFMs and DFMs at 30 stations in the east coast region of the United States are used to demonstrate a study on locating their source regions with reasonable certainty and constructing the functional relationship between the HVSRf_(0) and the source energy of SFMs and DFMs.The recordings are processed in four sub-frequency bands(Fs)of SF and DF bands and a polarization analysis is carried out to select the ellipsoids approximating the particle motions of Rg waves.Then the probability density functions of the back azimuths of the ellipsoids’semi-major axes are computed for each F and station,and are projected on the ocean to determine their possible source regions.These regions are further constrained by(1)the correlation coefficients between the SFMs and the WAVEWATCHⅢ(WWⅢ)hindcasts of ocean wave spectra in the SF band,or between the DFMs and the modeled DF energy on ocean surface in the selected time windows in the DF band,(2)the energy contribution defined by(i)the average WWⅢocean wave energy and the ocean bottom topographical gradient in the SF band,or(ii)the average modeled DF energy on ocean surface and a frequency and water depth dependent coefficient measuring the conversion efficiency of DF energy from water to solid earth in the DF band,and(3)the percentile retained energy of Rg waves in both the SF and DF bands.Results of source regions reveal that(1)the SFMs recorded in eastern US result from the interactions of low frequency(0.05-0.085 Hz)ocean waves with the continental slope and shelf of western North Atlantic Ocean;(2)the source regions for long-(0.1-0.2 Hz)period DFMs are located in the deep ocean close to the continental slope;and(3)the short-(0.2–0.5 Hz)period DFMs are generated in the continental shelf.Finally,the correlation analyses between the simulated source energy and the HVSRf_(0) values at the stations whose f_(0) s fall in DF band are carried out revealing significant source effect on thick sediments at low frequencies.

Dynamical analysis of the effect of elliptically polarized laser pulses on molecular alignment and orientation

In this Letter, we study the molecular alignment and orientation driven by two elliptically polarized laser pulses.It is shown that the field-free molecular alignment can be achieved in a three-dimensional（3D） case, while the field-free molecular orientation is only along the x and y directions, and that the field-free alignment and orientation along different axes are related to the populations of the rotational states. It is demonstrated that changing the elliptic parameter is efficient for controlling both in-pulse and post-pulse molecular alignment and orientation. The delay time also has an influence on the field-free molecular alignment and orientation.

Theoretical analysis of polarization control for the stable output of multi-carrier source based on a re-circulating frequency shifter

Fluctuating polarization state-of-light in the optical loop is an important factor that seriously influences the output performance of a multi-carrier source based on re-circulating frequency shifter （RFS）. The reason for output spectrum instability when no polarization controller （PC） is present in the loop is analyzed theoretically. Numerical simulations for the output spectra of the multi-carrier source with and without PC are conducted, and the trajectories of the several frequency components polarization states on the Poincare sphere with and without PC are compared. The results show that the performance of multi-carrier source based on a RFS can be improved effectively by adjusting the PC in the configuration properly.