Extending Loffeld's bistatic formula for the general bistatic SAR configuration

This study derives an accurate bistatic point target reference spectrum based on a zeroth-order polynomial model. The spectrum contains only two hyperbolic square root terms that are very analogous in form to the analytical monostatic spectrum. The new formulation can be considered as an improvement of the Loffeld?s bistatic formula (LBF) and allows it to handle a wider range of bistatic configurations. The original LBF works well only in the case where the contributions of transmitter and receiver to the total Doppler modulation are approximately equal. An earlier paper on the extended LBF (EBLF) uses time bandwidth product (TBP) to weight the azimuth phase modulation from each platform. However, this extension is valid only in the low squint bistatic geometry. Both LBF and ELBF are expanded up to the quadratic term to derive an approximate bistatic spectrum; however, they do not show a good focusing performance in the more complex bistatic geometry, for example, the high squint case. This is due to the inaccurate individual time- Doppler correspondences. In this study, a norm in Euclidean space is defined to derive the optimal individual time-Doppler correspondences. Using the accurate individual time-Doppler correspondences, a zeroth-order polynomial model can be used to readily derive a more accurate bistatic spectrum. Two simulation experiments in the high squint geometry are used to verify the accuracy of this new formulation. The first experiment uses a parallel-track spaceborne/spaceborne configuration, and the second experiment involves an orthogonal-track airborne/airborne case.     

Can screening for IgG antibodies against Helicobacter pylori be used in clinical practice? Omit endoscopy in seropositive or seronegative patients?

The objective of this study was to test the feasibility of a screening strategy for IgG antibodies against Helicobacter pylori in patients presenting with upper abdominal complaints. Biopsy specimens were taken for histological and microbiological investigations from consecutive patients undergoing upper gastrointestinal endoscopy. In addition, a serum sample was taken for detection of IgG antibodies against Helicobacter pylori, using an ELISA technique. Serum samples from 1294 consecutive patients were available. IgG antibodies against Helicobacter pylori were present in 622 patients (48%), the remaining 671 (52%) were negative. If endoscopy had been omitted in seronegative patients below the age of 45 years, this would have resulted in 234 patients not endoscoped. However, it can be assumed that 62 of these patients would undergo endoscopy because of recurrent complaints due to underlying disease or abnormality. Therefore 182 of 1294 (14%) of endoscopies would have been avoided. Application of this strategy on the total group of seronegatives would save 353 of 1294 (27.3%) endoscopies. If endoscopy had been omitted in seropositive cases below the age of 45 years, and these patients were treated with anti-Helicobacter therapy, an initial 145 endoscopies would have been avoided. However, 26 of these patients would undergo endoscopy because of persistent complaints due to underlying disease. Therefore 119 (9%) endoscopies would have been avoided. Applying this strategy in the total group of seropositives would have saved 434 of 1294 endoscopies (34%). Applying the IgG screening strategy in all patients would result in a significant number of endoscopies being avoided in the seropositive group, 434 versus 353 (P < 0.001). In conclusion, omitting endoscopy in seropositive cases, regardless of age, can reduce the workload more than omitting endoscopy in seronegative cases: 34% fewer endoscopies versus 27%.     

cis/trans isomerization of unsaturated fatty acids as possible control mechanism of membrane fluidity inPseudomonas putida P8

Exponentially growing cells ofPseudomonas putida had an increased ratio of saturated to unsaturated fatty acids in response to increased growth temperatures. Resting cells in which fatty acid biosynthesis was stopped reacted to a thermal increase by convertingcis-monounsaturated fatty acids totrans isomers.cis/trans isomerization of up to 60% of the unsaturated fatty acids was also activated by alcohols of different chain length. Their effective concentrations apparently depended on the lipophilic character of the alcohols. Also, a salt shock caused by the addition of NaCl resulted in the production oftrans fatty acids. However, cells that were adapted to growth media of high osmolarity synthesized cyclopropane fatty acids instead oftrans fatty acids. Activity ofcis/trans-isomerase was dependent on the growth phase and was significantly higher during logarithmic growth than during the stationary phase. The results of this study agree with the hypothesis that the isomerization ofcis intotrans unsaturated fatty acids is an emergency action of cells ofP. putida to adapt membrane fluidity to drastic changes of environmental conditions.     

Increasing the accuracy of Time-of-Flight cameras for machine vision applications

Range imaging based on the Time-of-Flight (ToF) principle evolved largely in recent years. Especially, the lateral resolution, the ability to operate outdoors with sunlight and the sensitivity have been improved. Nevertheless, the acceptance of depth cameras for machine vision in the industry environment is still rather limited. The major shortcoming of ToF depth cameras compared to laser range scanners is their measuring accuracy, which is not sufficient for several applications. In this paper, we firstly introduce several state of the art depth cameras briefly and demonstrate their capabilities. Afterwards, we explore possibilities to increase the radial resolution and the accuracy of ToF depth cameras based on the Photonic Mixer Device (PMD). In general, the usage of higher modulation frequencies promises higher depth resolution but yields on the other hand higher noise levels. Moreover, the accuracy is limited by systematic errors and the measurement are affected by random noise and we show how to minimize and compensate them in industry environments.     

cis/trans isomerization of unsaturated fatty acids as possible control mechanism of membrane fluidity in Pseudomonas putida P8

OBJECTIVE: To determine the effect of different motor learning schedules on stroke patients' rate of acquisition and retention of a functional movement sequence using the hemiparetic upper limb. DESIGN: Randomized controlled group study using a retention design with two retention trials. SETTING: Outpatient neurorehabilitation clinic. PATIENTS: Twenty-four patients with chronic hemiparesis secondary to a single unilateral cerebral stroke without evidence of severe cognitive or language impairment. MAIN OUTCOME MEASURE: The primary hypothesis was that hemiparetic motor learning that occurred under conditions of contextual interference (ie, random practice) would be retained better than learning that occurred under conditions of repetitive drill (blocked practice). RESULTS: A significant difference was found among the three groups (ie, random-practice, blocked-practice, control) on both the first retention measure (chi 2 = 13.50, p < .01) and the second retention measure (chi 2 = 12.59, p < .01). More importantly, a significant difference was found between the random-practice and blocked-practice groups on both the first retention measure (U = 68.5, p < .01) and the second retention measure (U = 62.0, p = .05). CONCLUSIONS: Findings provide empirical evidence to support the contention that random practice is more effective than blocked practice, with respect to retention over time, when hemiparetic stroke patients attempt to learn functional motor skills.     

双基SAR成像的点目标解析频谱研究

双基SAR距离徙动由于存在两个双曲线形式,使用传统的驻定相位原理方法难以解析得到双基下的目标二维频谱。该文总结了LBF方法,级数反演方法,利用双基成像几何的瞬时频率方法以及基于等效单基思想的DMO方法,并给出了必要的分析,给出了DMO方法和GBF的等效性,验证了在任意构型下级数反演方法和LBF的关系。通过不同双基构型下的点目标成像仿真结果详细分析了各种方法的聚焦性能。     

Phase Unwrapping for SAR Interferometry—A Data Fusion Approach by Kalman Filtering

This paper considers the problem of unwrapping the phase image obtained from a noisy interferometric synthetic aperture radar (InSAR) image. The implicit nonlinearity of the problem is reflected, as well as the drawbacks of this nonlinearity on the performance of phase unwrapping approaches. Some general concepts concerning basic estimation techniques are shortly reviewed. On this background, a Kalman filter-based data fusion approach to unwrap and simultaneously filter the phases of InSAR images is developed. The data fusion concept exploits phase information extracted from the complex interferogram rather than from the phase image and fuses that information with phase slope information extracted from the power spectral density of the interferogram.     

异构平台双基SAR成像的RD算法

LBF是第一个原理上适用于任意构型双基SAR的点目标二维解析频谱.传统的LBF对于速度差异较大的异种平台构型双基SAR的精度低,无法实现有效聚焦成像处理.本文给出了一种基于加权LBF的双基SAR的RD算法.仿真成像结果验证了所提方法的有效性.     

Bistatic point target reference spectrum in the presence of trajectory deviations

The point target reference spectrum (BPTRS) of bistatic SAR in the presence of trajectory deviations based on Loffeld?s bistatic formula (LBF) is developed. The presented BPTRS is suitable for the general airborne bistatic configuration. For the air-borne bistatic SAR, both the transmitter and the receiver will contribute to the trajectory deviation. The compensation of trajectory deviations becomes more complex because of the separate locations of the transmitter and receiver. The authors focus on the effects of trajectory deviations on the point target spectrum of bistatic SAR. The proposed BPTRS is verified by simulation experiments performed in the azimuth-invariant configuration.