On the detection of underwater bottom topography by imaging radars

A theoretical model which explains basic properties of radar imaging of underwater bottom topography in tidal channels is presented. The surface roughness modulation is described by weak hydrodynamic interaction theory in the relaxation time approximation. In contrast to previous theories on short wave modulation by long ocean waves, a different approximation is used to describe short wave modulation by tidal flow over underwater bottom topography. The modulation depth is proportional to the relaxation time of the Bragg waves. The large modulation of radar reflectivity observed in SEASAT-SAR imagery of sand banks in the Southern Bight of the North Sea are explained by assuming that the relaxation time of 34 cm Bragg waves is of the order of 30-40 seconds

A perturbation approach to coherent propagation of energetic charged particles in random magnetic fields

The Fokker-Planck equation describing the propagation of charged particles in magnetic fields that consist of a dominant constant guiding field and superposed random fluctuations is solved by applying the perturbation method of dividing the total particle density into an averaged isotropic and a small anisotropic component. A particle transport equation is derived which describes the 'coherent' propagation of a particle pulse whose center moves at half the constant total particle velocity in either the positive or negative direction. The range of validity of the coherent solution is examined, and the general formulas for coherent propagation are applied to the slab, isotropic, and Alfven-wave models of magnetic-field fluctuations. Ranges of magnetic-fluctuation spectral indices are identified over which diffusive and coherent particle-transport modes can exist in the three models considered

Measurements at 13.9 GHz of the radar backscattering cross section of the North Sea covered with an artificial surface film

The reduction of the Ku‐band (13.9 GHz) normalized radar cross section (NRCS) by an artificial monomolecular surface film (oleyl alcohol) on the sea surface was measured in the North Sea during the 1975 Joint North Sea Wave Project, JONSWAP 75 experiment. The aim of the surface film experiment was to simulate natural surface films which often occur on the ocean surface and are produced by plankton or fish. NRCS measurements were obtained from an aircraft at incidence angles of 41° and 47° at vertical and horizontal polarizations. For winds between 3.5 and 4.4 m/sec the maximum measured reduction was 7.3 ± 3.5 dB relative to the mean. In‐situ measurements showed that the oleyl alcohol film reduced the surface tension from 74 to 43 dyne/cm. Similar reductions in surface tension have also been measured on the ocean due to natural surface films of biological origin. It is noted that variations of the NRCS due to natural surface film effects may significantly limit the techniques used currently to infer surface wind vector over biologically active ocean regions

Generation of secondary internal waves by the interaction of an internal solitary wave with an underwater bank

The generation of secondary internal waves by the interaction of a large-amplitude internal solitary wave with the Dreadnought Bank in the Andaman Sea (6°40′N, 95° 47′E) is shown by analyzing a synthetic aperture radar (SAR) image acquired by the European Remote Sensing satellite ERS-2 and by carrying out model calculations. Although the Dreadnought Bank is quite deep (241 m), the model calculations show that large-amplitude internal solitary waves as encountered in this sea area can overturn and break over the bank and generate secondary internal waves. Comparison of model results with observations clearly demonstrates that the semicircular wave pattern visible on the ERS-2 SAR image centered at the Dreadnought Bank is indeed a sea surface manifestation of a secondary internal wave packet generated by scattering of a large-amplitude internal solitary wave and not by the interaction of the barotropic tidal flux with this underwater obstacle. Copyright 2005 by the American Geophysical Union

A theory of the imaging mechanism of underwater bottom topography by real and synthetic aperture radar

A simple theoretical model of the imaging mechanism of underwater bottom topography in tidal channels by real and by synthetic aperture radar (SAR) is presented. The imaging is attributed to surface effects induced by current variations over bottom topography. The current modulates the short-scale surface roughness, which in turn gives rise to changes in radar reflectivity. The bottom topography- current interaction is described by the continuity equation, and the current-short surface wave interac- tion is described by weak hydrodynamic interaction theory in the relaxation time approximation. This theory contains only one free parameter, which is the relaxation time. It is shown that in the case of tidal flow over large-scale bottom topographic features, e.g., over sandbanks, the radar cross-section modulation is proportional to the product of the relaxation time and the gradient of the surface current velocity, which is proportional to the slope of the water depth divided by the square of the depth. To first order, tiffs modulation is independent of wind direction. In the case of SAR imaging, in addition to the above mentioned hydrodynamic modulation, phase modulation or velocity bunching also contributes to the imaging. However, in general, the phase modulation is small in comparison to the hydrodynamic modu- lation. The theory is confronted with experimental data which show that to first order our theory is capable of explaining basic features of the radar imaging mechanism of underwater bottom topography in tidal channels. I n order to explain the large observed modulation of radar reflectivity we are compelled to assume a large relaxation time, which for Seasat SAR Bragg waves (wavelength 34 cm) is of the order of 30-40 s, corresponding to 60-80 wave periods

Happy Mouth and Sad Eyes : Scanning Emotional Facial Expressions

There is evidence that specific regions of the face such as the eyes are particularly relevant for the decoding of emotional expressions, but it has not been examined whether scan paths of observers vary for facial expressions with different emotional content. In this study, eye-tracking was used to monitor scanning behavior of healthy participants while looking at different facial expressions. Locations of fixations and their durations were recorded, and a dominance ratio (i.e., eyes and mouth relative to the rest of the face) was calculated. Across all emotional expressions, initial fixations were most frequently directed to either the eyes or the mouth. Especially in sad facial expressions, participants more frequently issued the initial fixation to the eyes compared with all other expressions. In happy facial expressions, participants fixated the mouth region for a longer time across all trials. For fearful and neutral facial expressions, the dominance ratio indicated that both the eyes and mouth are equally important. However, in sad and angry facial expressions, the eyes received more attention than the mouth. These results confirm the relevance of the eyes and mouth in emotional decoding, but they also demonstrate that not all facial expressions with different emotional content are decoded equally. Our data suggest that people look at regions that are most characteristic for each emotion

Hyperglycemia and Hyperlipidemia Act Synergistically to Induce Renal Disease in LDL Receptor-Deficient BALB Mice

Diabetic nephropathy is the leading cause of end-stage renal disease in Western countries, but only a portion of diabetic patients develop diabetic nephropathy. Dyslipidemia represents an important aspect of the metabolic imbalance in diabetic patients. In this study, we addressed the impact of combined hyperlipidemia and hyperglycemia on renal pathology. Kidneys from wildtype (WT) or LDL receptor-deficient BALB/cBy mice (BALB. LDLR -/-) were examined at 22 weeks of age. Diabetes was induced by administration of streptozotocin and mice were randomly assigned to either standard chow or Western diet. Chow fed BALB. LDLR -/- mice did not demonstrate renal abnormalities, whereas BALB. LDLR -/- mice fed a Western diet showed occasional glomerular and tubulointerstitial foam cells. Diabetic WT mice had modestly increased glomerular cellularity and extracellular matrix. Hyperlipidemic and diabetic BALB. LDLR -/- mice exhibited an increase in glomerular cellularity and extracellular matrix, accumulation of glomerular and tubulointerstitial foam cells and mesangial lipid deposits. The tubular epithelium demonstrated pronounced lipid induced tubular degeneration with increased tubular epithelial cell turnover. Hyperlipidemia and hyperglycemia seem to act synergistically in inducing renal injury in the BALB. LDLR-/- mouse. This model of diabetic nephropathy is unique in its development of tubular lesions and may represent a good model for hyperlipidemia-exacerbated diabetic nephropathy. Copyright (C) 2004 S. Karger AG, Basel

DETECTING PANIC POTENTIAL IN SOCIAL MEDIA TWEETS

A high degree of real-time interconnectedness can aid information transmission, particularly in disaster situations. However, it can have substantial negative consequences when information is emotionally laden and transmits these emotions, particularly the emotion of panic, to the individual across social media in an already grave situation. Prior research has shown that information laden with emotion spreads through social network faster than otherwise. Hence, we highlight the need to understand and curtail potentially panic-causing information, without compromising on good quality information from being available for effective crisis communication and management. With this research, we present the necessity of detecting the panic potential of social media messages, and aim to address two research questions: What are the features, and metrics necessary, to compute and evaluate the panic potential of a social media message (respectively)? Our planned analysis takes the case of the Munich shooting incident, 2016, based on user tweets immediately after the incident. Different features and evaluation metrics are proposed and discussed. The work aims to detect panic potential of messages in social media networks during disasters