scholarly journals A Novel Microwave Staring Correlated Radar Imaging Method Based on Bi-Static Radar System

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 879 ◽  
Author(s):  
Bo Yuan ◽  
Yuanyue Guo ◽  
Weidong Chen ◽  
Dongjin Wang
Keyword(s):  
Radiation Field ◽  
Beam Width ◽  
Frequency Hopping ◽  
Pulse Frequency ◽  
Imaging Method ◽  
Space Correlation ◽  
Imaging Geometry ◽  
Radiation Fields ◽  
Stochastic Characteristic ◽  
The One

The stochastic characteristic of the radiation field of a mono-static microwave staring correlated imaging (MSCI) radar degenerates with the increase of the imaging distance, which results in degradation of the image quality. To address this issue, a novel MSCI method based on bi-static radar is proposed from two perspectives: site-deploying and waveform design. On the one hand, a new bi-static MSCI site-deploying scheme is proposed which adopts two transmitting stations with their azimuth angles relative to the center of the imaging region differing by 90 degrees. On the other hand, by using two transmitting arrays synchronously transmitting inner-and-inter pulse frequency hopping (IAIP-FH) signals, the radiation field of each station includes a few “frequency stripes” perpendicular to the radiation direction, and as a consequence, the “frequency stripes” of each radiation field are perpendicular to each other. As a result, the radiation field of the bi-static MSCI is the superposition of the two striped radiation fields, thus a latticed radiation field is constructed. Therefore, the targets in different latticed grids scatter independent fields, then, the images can be reconstructed using correlation process (CP) algorithms. The grid size of the latticed radiation field is determined by the inner-pulse frequency hopping (FH) interval of the IAIP-FH signals and the imaging geometry. Moreover, it is shown that the 3 dB beam width of the space correlation function of the radiation field does not change with the imaging distance, thus the stochastic characteristic of the radiation field is partly preserved when the imaging distance increases. Simulation results validate the analysis and show that the proposed method can obtain higher resolution images than the common mono-static MSCI method.

scholarly journals Radiative cooling rates, ion fractions, molecule abundances, and line emissivities including self-shielding and both local and metagalactic radiation fields

2020 ◽  
Vol 497 (4) ◽  
pp. 4857-4883 ◽  
Author(s):  
Sylvia Ploeckinger ◽  
Joop Schaye
Keyword(s):  
Cosmic Rays ◽  
Radiation Field ◽  
Spectral Synthesis ◽  
Cosmic Ray ◽  
Cooling Rates ◽  
Radiation Fields ◽  
Hydrodynamical Simulations ◽  
Lower Temperature ◽  
X Ray Background ◽  
Ionization Balance

ABSTRACT We use the spectral synthesis code cloudy to tabulate the properties of gas for an extensive range in redshift (z = 0–9), temperature (log T[K] = 1–9.5), metallicity (log Z/Z⊙ = −4 – +0.5, Z = 0), and density ($\log n_{\mathrm{H}}[\, \mathrm{cm}^{-3}] = -8$ − +6). This therefore includes gas with properties characteristic of the interstellar, circumgalactic, and intergalactic media. The gas is exposed to a redshift-dependent UV/X-ray background, while for the self-shielded lower-temperature gas (i.e. ISM gas), an interstellar radiation field and cosmic rays are added. The radiation field is attenuated by a density- and temperature-dependent column of gas and dust. Motivated by the observed star formation law, this gas column density also determines the intensity of the interstellar radiation field and the cosmic ray density. The ionization balance, molecule fractions, cooling rates, line emissivities, and equilibrium temperatures are calculated self-consistently. We include dust, cosmic rays, and the interstellar radiation field step-by-step to study their relative impact. These publicly available tables are ideal for hydrodynamical simulations. They can be used stand alone or coupled to a non-equilibrium network for a subset of elements. The release includes a C routine to read in and interpolate the tables, as well as an easy-to-use python graphical user interface to explore the tables.

scholarly journals Modeling Compact Intracloud Discharge (CID) as a Streamer Burst

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 549
Author(s):  
Vernon Cooray ◽  
Gerald Cooray ◽  
Marcos Rubinstein ◽  
Farhad Rachidi
Keyword(s):  
Electric Field ◽  
Electrical Activity ◽  
Radiation Field ◽  
Time Derivative ◽  
Vertical Direction ◽  
Maximum Growth ◽  
Nanosecond Duration ◽  
Peak Current ◽  
Radiation Fields ◽  
Large Current

Narrow Bipolar Pulses are generated by bursts of electrical activity in the cloud and these are referred to as Compact Intracloud Discharges (CID) or Narrow Bipolar Events in the current literature. These discharges usually occur in isolation without much electrical activity before or after the event, but sometimes they are observed to initiate lightning flashes. In this paper, we have studied the features of CIDs assuming that they consist of streamer bursts without any conducting channels. A typical CID may contain about 109 streamer heads during the time of its maximum growth. A CID consists of a current front of several nanosecond duration that travels forward with the speed of the streamers. The amplitude of this current front increases initially during the streamer growth and decays subsequently as the streamer burst continues to propagate. Depending on the conductivity of the streamer channels, there could be a low-level current flow behind this current front which transports negative charge towards the streamer origin. The features of the current associated with the CID are very different from those of the radiation field that it generates. The duration of the radiation field of a CID is about 10–20 μs, whereas the duration of the propagating current pulse associated with the CID is no more than a few nanoseconds in duration. The peak current of a CID is the result of a multitude of small currents associated with a large number of streamers and, if all the forward moving streamer heads are located on a single horizontal plane, the cumulative current that radiates at its peak value could be about 108 A. On the other hand, the current associated with an individual streamer is no more than a few hundreds of mA. However, if the location of the forward moving streamer heads are spread in a vertical direction, the peak current can be reduced considerably. Moreover, this large current is spread over an area of several tens to several hundreds of square meters. The study shows that the streamer model of the CID could explain the fine structure of the radiation fields present both in the electric field and electric field time derivative.

scholarly journals Accretion-Disk Corona Advected by External Radiation Drag

1998 ◽  
Vol 188 ◽  
pp. 413-414
Author(s):  
Y. Watanabe ◽  
J. Fukue
Keyword(s):  
Angular Momentum ◽  
Radiation Field ◽  
Accretion Disk ◽  
Accretion Disks ◽  
External Radiation ◽  
Radiation Fields ◽  
Almost All ◽  
Strong Radiation ◽  
Radiative Interaction ◽  
Standard Disk

Accretion-disk corona (ADC) is required from observational as well as theoretical reasons. In almost all of traditional studies, however, a stationary corona has been assumed; i.e., the corona gas corotates with the underlying (Keplerian) accretion disk, and the radial motion is ignored. Recently, in the theory of accretion disks a radiative interaction between the gas and the external radiation field has attracted the attention of researchers. In particular the radiation drag between the gas and the external radiation field becomes important from the viewpoint of the angular-momentum removal. We thus examine the effect of radiation drag on the accretion-disk corona above/below the accretion disk (Watanabe, Fukue 1996a, b). We suppose that an accretion disk can be described by the standard disk, and that radiation fields are produced by the central luminous source and the accretion disk, itself. In general an accretion-disk corona under the influence of strong radiation fields dynamically infalls (advected) toward the center.

A New Imaging Method for Circular Trace Scanning SAR with Wide Observation

2014 ◽  
Vol 716-717 ◽  
pp. 1047-1050
Author(s):  
Huai Jiang ◽  
Min Han ◽  
Hui Chang Zhao
Keyword(s):  
Order Approximation ◽  
Inversion Method ◽  
Imaging Method ◽  
Imaging Geometry ◽  
Sar Imaging ◽  
Distance Model ◽  
Coupling Terms ◽  
Simulation Results ◽  
Imaging Speed

Circular Trace Scanning SAR is a new strip map mode SAR imaging in recent years, its imaging speed is fast with larger scene. This paper first establishes the imaging geometry right, by the four order approximation of the oblique distance model, combined with the series inversion method, and the removal of the coupling terms in the spectrum in the range Doppler domain, finally complete the azimuth compression. The simulation results prove the validity and feasibility of the imaging.

Exact solutions of the field equations: twist-free pure radiation fields

1962 ◽  
Vol 270 (1342) ◽  
pp. 328-334 ◽  
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Radiation Field ◽  
Relativity Theory ◽  
Vacuum Field ◽  
Field Equations ◽  
General Relativity Theory ◽  
Pure Radiation ◽  
Radiation Fields ◽  
Null Congruence

This note is intended to give a rough survey of the results obtained in the study of twist-free pure radiation fields in general relativity theory. Here we are using the following Definition. A space-time ( V 4 of signature +2) is called a pure radiation field if it contains a distortion-free geodetic null congruence (a so-called ray congruence ), and if it satisfies certain field equations which we will specify below (e.g. Einstein’s vacuum-field equations). A (null) congruence is called twist-free if it is hypersurface-orthogonal (or ‘normal’). The results listed below were obtained by introducing special (‘canonical’) co-ordinates adapted to the ray congruence. Detailed proofs were given by Robinson & Trautman (1962) and by Jordan, Kundt & Ehlers (1961) (see also Kundt 1961). For the sake of completeness we include in our survey the subclass of expanding fields, and make use of some formulae first obtained by Robinson & Trautman.

scholarly journals 9.17. Accretion disk winds driven by the disk radiation field under radiation drag

1998 ◽  
Vol 184 ◽  
pp. 415-416
Author(s):  
Y. Tajima ◽  
J. Fukue
Keyword(s):  
Radiation Field ◽  
Accretion Disk ◽  
Ionized Gas ◽  
Radiation Fields ◽  
Intense Radiation

The radiative winds from a geometrically thin accretion disk are studied. The effect of radiation drag which causes in the intense radiation fields around the accretion disk is examined recently. Then, we numerically consider the radiatively-accelerated accretion-disk winds which consist of ionized gas particles, taking into account radiation drag of the order ofv/c.

scholarly journals Relationship between pneumonitis induced by immune checkpoint inhibitors and the underlying parenchymal status: a retrospective study

2020 ◽  
Vol 6 (1) ◽  
pp. 00165-2019 ◽  
Author(s):  
Chiara Pozzessere ◽  
Hasna Bouchaab ◽  
Raphael Jumeau ◽  
Igor Letovanec ◽  
Cécile Daccord ◽  
...  
Keyword(s):  
Radiation Field ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitors ◽  
Checkpoint Inhibitors ◽  
Primary Tumour ◽  
Treatment Interruption ◽  
Immunosuppressive Drug ◽  
Lung Tumour ◽  
Radiation Fields ◽  
Tumour Metastasis

In patients with primary or secondary lung tumour treated with immune checkpoint inhibitors, immune-related pneumonitis is a rare adverse event but may evolve to respiratory failure. Prompt management is required and usually consists of treatment interruption and immunosuppressive drug administration. The aim of this study was to evaluate relationships between immune-related pneumonitis and pre-existing parenchymal status, especially tumour location and history of chest radiotherapy.Computed tomography (CT) scans of patients with immune-related pneumonitis were retrospectively reviewed. Pattern, distribution and extent of pneumonitis were assessed in six lung regions. In patients who received radiotherapy, the extent of pneumonitis was evaluated according to the radiation field.Among 253 patients treated with immunotherapy, 15 cases of immune-related pneumonitis were identified. 10 had previous or concomitant chest radiotherapy in addition to immunotherapy. At CT scan, 29 (33%) out of 88 regions encompassed the primary tumour (n=4), a lung metastasis (n=4) and/or radiation fields (n=21). A significantly higher prevalence of parenchymal involvement by immune-related pneumonitis occurred within areas of primary or metastatic malignancy and/or radiation field (97%) as compared to other areas (3%, p=0.009). Lung regions affected by the primary tumour, metastasis or radiotherapy had a higher probability of immune-related pneumonitis than others (OR 10.8, p=0.024). An organising pneumonia (OP) pattern was more frequent after radiotherapy (70% versus 0%, p=0.024), whereas nonspecific interstitial pneumonia features were more commonly seen in radiotherapy-naive patients (100% versus 10%, p=0.002).In patients with primary or secondary lung tumour treated with immune checkpoint inhibitors, immune-related pneumonitis is preferentially located within lung areas involved by tumour and/or radiation fields.

scholarly journals Research of a Radar Imaging Algorithm Based on High Pulse Repetition Random Frequency Hopping Synthetic Wideband Waveform

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5424 ◽  
Author(s):  
Songhua He ◽  
Xiaotian Wu
Keyword(s):  
Pulse Compression ◽  
Coupling Effect ◽  
Frequency Hopping ◽  
Pulse Repetition ◽  
Imaging Method ◽  
Image Processing Algorithm ◽  
Compression Process ◽  
Imaging Algorithm ◽  
Random Frequency ◽  
High Pulse

Aiming at the imaging algorithm of high-pulse-repetition random-frequency-hopping synthetic wideband radar on a supersonic/hypersonic aircraft platform, this study established an echo simulation model of target and clutter, analyzed the special range-Doppler coupling effect and its influence on imaging, and proposes a method of imaging with pipeline-parallel processing based on generalized 2D matched-filtering and Doppler pre-processing. In the method, Doppler-beam-sharpening was advanced to be performed with the pulse compression process in each frame, and the special range-Doppler coupling effect caused by high dynamic motion of platform and random frequency hopping in bandwidth synthesis was well suppressed; several modes of random frequency hopping were designed and the pipeline-parallel image processing algorithm was optimized for each mode. Theoretical analysis and simulation results show that the proposed imaging method can effectively avoid the divergence of 2D range-Doppler images in the range direction, and can meet the requirements of real-time imaging.

Detection of Groundwater Aquifer Using Resistivity Imaging Profiling at Beriah Landfill Site, Perak, Malaysia

2011 ◽  
Vol 250-253 ◽  
pp. 1852-1855 ◽  
Author(s):  
Mohd Hafiz Zawawi ◽  
Syafalni ◽  
Ismail Abustan
Keyword(s):  
Ground Surface ◽  
Underground Water ◽  
Two Dimensions ◽  
Landfill Site ◽  
Imaging Method ◽  
Resistivity Imaging ◽  
Groundwater Aquifer ◽  
Resistivity Inversion ◽  
The One ◽  
Resistivity Meter

This study explains the use of resistivity imaging profiling. The Resistivity Imaging Profiling (RIP) became the one of some important techniques in order to get more information for finding out some hidden water in geophysical survey and this has been applied in Beriah Landfill Site in task of exploring the location storing underground water. Two dimensional geoelectrical imaging has been applied for this study. The method can be used for map the distribution of resistivity for the subsurface materials layer. The principle goals of this survey are to define the depth of aquifer layers from the subsoil, the water table and the depth of bedrock as well as suitable site for well. The imaging method was used in this study to map the subsurface soil and groundwater in and around the landfill area that includes six resistivity line. Surveys were conducted using SAS4000 resistivity meter and ABEM LUND electrode and the measured resistivity profiles were interpreted with 2-D resistivity inversion programme (RES2DINV) software presented by two dimensions which is axis-x represent as a length on the ground surface while axis-y referred to the depth of the subsurface in meter.

Two Methods to Test Transducer Array Directivity

2014 ◽  
Vol 912-914 ◽  
pp. 1485-1488
Author(s):  
Hong Liu ◽  
Guo Zhu Zhao
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Beam Width ◽  
Directivity Pattern ◽  
Acute Angle ◽  
Pressure Level ◽  
The Other ◽  
Transducer Array ◽  
Acoustic Transducer ◽  
The One

An array which possess more array element number and whose frequency of the drive signal can be as large as possible in a range, directivity will be more preferable. On the other hand, when the structure of the sound radiating surface of the transducer or array layout is symmetrical, the corresponding directivity pattern will be symmetrical. In order to test transducer directivity, two methods are designed. The one is to measure the ultrasonic sound pressure level by instruments. The sound pressure level is measured at multiple points to deduce the directivity angle of the acoustic transducer array. The beam width of the 3×3 array is about at 23kHz, and the directivity acute angle is about 10°; higher frequencies will lead to the side lobes, but it can be negligible when compared to the main lobe. The other method is using the frequency analyzer to test transducer directivity in a silencer chamber. The sound pressure level can be read out from frequency response diagrams. The angle between the sound pressure value that decreasing 3db from the max value 111.7db and the max value is about 11°. So the directivity acute angle is about 11°. It should be noticed that, as the directivity diagram can not be directly attributed, there is some deviation in the conclusion.

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