17 results on '"V. Lehman"'
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2. Mean wind vector estimation using the velocity–azimuth display (VAD) method: an explicit algebraic solution
- Author
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G. Teschke and V. Lehmann
- Subjects
Environmental engineering ,TA170-171 ,Earthwork. Foundations ,TA715-787 - Abstract
This paper deals with the analysis of the sampling setup for Doppler profilers aiming at the determination of vertical profiles of the wind. An explicit solution for the retrieval of mean wind vectors under the assumption of local homogeneity is presented for the case of a symmetric velocity–azimuth display sampling, and a stability analysis is performed. Furthermore, the explicit solution allows a detailed investigation of the propagation of radial wind measurement errors on the retrieved wind vector. more...
- Published
- 2017
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3. Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler
- Author
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J. Bühl, R. Leinweber, U. Görsdorf, M. Radenz, A. Ansmann, and V. Lehmann
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Environmental engineering ,TA170-171 ,Earthwork. Foundations ,TA715-787 - Abstract
Case studies of combined vertical-velocity measurements of Doppler lidar, cloud radar and wind profiler are presented. The measurements were taken at the Meteorological Observatory, Lindenberg, Germany. Synergistic products are presented that are derived from the vertical-velocity measurements of the three instruments: a comprehensive classification mask of vertically moving atmospheric targets and the terminal fall velocity of water droplets and ice crystals corrected for vertical air motion. It is shown that this combination of instruments can up-value the measurement values of each single instrument and may allow the simultaneous sensing of atmospheric targets and the motion of clear air. more...
- Published
- 2015
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4. An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial
- Author
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E. Päschke, R. Leinweber, and V. Lehmann
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Environmental engineering ,TA170-171 ,Earthwork. Foundations ,TA715-787 - Abstract
We present the results of a 1-year quasi-operational testing of the 1.5 μm StreamLine Doppler lidar developed by Halo Photonics from 2 October 2012 to 2 October 2013. The system was configured to continuously perform a velocity-azimuth display scan pattern using 24 azimuthal directions with a constant beam elevation angle of 75°. Radial wind estimates were selected using a rather conservative signal-to-noise ratio based threshold of −18.2 dB (0.015). A 30 min average profile of the wind vector was calculated based on the assumption of a horizontally homogeneous wind field through a Moore–Penrose pseudoinverse of the overdetermined linear system. A strategy for the quality control of the retrieved wind vector components is outlined for ensuring consistency between the Doppler lidar wind products and the inherent assumptions employed in the wind vector retrieval. Quality-controlled lidar measurements were compared with independent reference data from a collocated operational 482 MHz radar wind profiler running in a four-beam Doppler beam swinging mode and winds from operational radiosonde measurements. The intercomparison results reveal a particularly good agreement between the Doppler lidar and the radar wind profiler, with root mean square errors ranging between 0.5 and 0.7 m s−1 for wind speed and between 5 and 10° for wind direction. The median of the half-hourly averaged wind speed for the intercomparison data set is 8.2 m s−1, with a lower quartile of 5.4 m s−1 and an upper quartile of 11.6 m s−1. more...
- Published
- 2015
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5. Advanced intermittent clutter filtering for radar wind profiler: signal separation through a Gabor frame expansion and its statistics
- Author
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V. Lehmann and G. Teschke
- Subjects
Science ,Physics ,QC1-999 ,Geophysics. Cosmic physics ,QC801-809 - Abstract
A new signal processing method is presented for the suppression of intermittent clutter echoes in radar wind profilers. This clutter type is a significant problem during the seasonal bird migration and often results in large discrepancies between profiler wind measurements and independent reference data. The technique presented makes use of a discrete Gabor frame expansion of the coherently averaged time series data in combination with a statistical filtering approach to exploit the different signal characteristics between signal and clutter. The rationale of this algorithm is outlined and the mathematical methods used are presented in due detail. A first test using data obtained with an operational 482 MHz wind profiler indicates that the method outperforms the previously used clutter suppression algorithm. more...
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- 2008
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6. Investigation of inertia-gravity waves in the upper troposphere/lower stratosphere over Northern Germany observed with collocated VHF/UHF radars
- Author
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A. Serafimovich, P. Hoffmann, D. Peters, and V. Lehmann
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Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
A case study to investigate the properties of inertia-gravity waves in the upper troposphere/lower stratosphere has been carried out over Northern Germany during the occurrence of an upper tropospheric jet in connection with a poleward Rossby wave breaking event from 17-19 December 1999. The investigations are based on the evaluation of continuous radar measurements with the OSWIN VHF radar at Kühlungsborn (54.1 N, 11.8 E) and the 482 MHz UHF wind profiler at Lindenberg (52.2 N, 14.1 E). Both radars are separated by about 265 km. Based on wavelet transformations of both data sets, the dominant vertical wavelengths of about 2-4 km for fixed times as well as the dominant observed periods of about 11 h and weaker oscillations with periods of 6 h for the altitude range between 5 and 8 km are comparable. Gravity wave parameters have been estimated at both locations separately and by a complex cross-spectral analysis of the data of both radars. The results show the appearance of dominating inertia-gravity waves with characteristic horizontal wavelengths of 300 km moving in the opposite direction than the mean background wind and a secondary less pronounced wave with a horizontal wavelength in the order of about 200 km moving with the wind. Temporal and spatial differences of the observed waves are discussed. more...
- Published
- 2005
7. Wavelet based methods for improved wind profiler signal processing
- Author
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V. Lehmann and G. Teschke
- Subjects
Science ,Physics ,QC1-999 ,Geophysics. Cosmic physics ,QC801-809 - Abstract
In this paper, we apply wavelet thresholding for removing automatically ground and intermittent clutter (airplane echoes) from wind profiler radar data. Using the concept of discrete multi-resolution analysis and non-parametric estimation theory, we develop wavelet domain thresholding rules, which allow us to identify the coefficients relevant for clutter and to suppress them in order to obtain filtered reconstructions.Key words. Meteorology and atmospheric dynamics (instruments and techniques) – Radio science (remote sensing; signal processing) more...
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- 2001
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8. Field campaign LINEX 96/1 — Possibilities of water vapor observation in the free atmosphere
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H. Steinhagen, S. Bakan, J. Bösenberg, H. Dier, D. Engelbart, J. Fischer, G. Gendt, U Görsdorf, J. Güldner, F. Jansen, V. Lehmann, U. Leiterer, J. Neisser, and Volker Wulfmeyer
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differential absorption lidar (dial) ,rawinsonde measurement ,tethersonde measurement ,bias ,wasserdampf ,differentieller absorptions-lidar (dial) ,Meteorology. Climatology ,QC851-999 - Abstract
LINEX 96/1 was a field experiment to assess information content, accuracy, and availability for different remote sensing techniques measuring water vapor. An important goal of LINEX 96/1 was the test of a new Differential Absorption Lidar (DIAL) developed by the MPI für Meteorologie Hamburg. Comparisons of DIAL with rawinsonde and tethersonde measurements showed an excellent accuracy of the DIAL method in the determination of water vapor with high vertical and temporal resolution. The operation of the microwave radiometer WVR-1100 showed a high availability of water vapor and liquid water column content measurements except during rain. Microwave radiometers are reliable systems to measure the precipitable water vapor and liquid water content under unattended operational conditions with high accuracy and temporal resolution. Measurements of the water vapor column content by groundbased GPS receivers proved highly reliable. Comparisons with corresponding values of the microwave radiometer showed a bias less than 0.6 mm and a standard deviation less than 0.9 mm. The main problem of an operational use of this new information is that the evaluated data are not available in real-time because, at present, the data have to be postprocessed in a ground control center. During LINEX 96/1, possibilities for estimation of water vapor column content from sun and star photometer measurements were also demonstrated. The comparison of the precipitable water vapor content measurements of sun and star photometers, microwave radiometer, and rawinsondes RS 80 showed a good agreement. Unfortunately, the use of optical methods like sun and star photometers is restricted by cloudy conditions. The field campaign LINEX 96/1 was an important contribution to the COST Action 76 by investigation of the new possibilities measuring water vapor in the free atmosphere with the objective of improvements of our knowledge about the 4-dimensional water vapor field. more...
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- 1998
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9. Performance of the first European 482 MHz Wind Profiler Radar with RASS under operational conditions
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H. Steinhagen, J. Dibbern, D. Engelbart, U. Görsdorf, V. Lehmann, J. Neisser, and J. W. Neuschaefer
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radio-acoustic sounding system ,Meteorology. Climatology ,QC851-999 - Abstract
The first 482 MHz Wind Profiler Radar (WPR) in Europe completed with a Radio-Acoustic Sounding System (RASS) has been operated at the Meteorological Observatory Lindenberg since July 3rd, 1996 after a comprehensive study regarding the investigation of frequency compatibility between the WPR and the television channel 22 (478-486 MHz). The WPR can operate with different height and time resolutions (e. g. 250 m in the so-called Low Mode or 500 m in the High Mode). A height range of up to approximately 16 km can be realized in the High Mode. The installed WPR/RASS combination allows also the measurement of profiles of the virtual temperature with the Low Mode resolution in the height range from 500 m up to approximately 4000 m. The main objective of this contribution is the investigation of the accuracy and the availability of this new remote sensing system. First results of the accuracy can be given on the base of about 1000 intercomparisons between WPR/RASS and Rawinsonde data. The bias of the horizontal wind velocities is less than 0.4 m/s in the Low Mode and 0.7 m/s in the High Mode (from 3 to 10 km) and therefore smaller than the average accuracy of both systems. The bias of the temperature measurements is less than 1 K and can be improved by some corrections in future. A first statistics of the data availability can be shown based on nearly 6000 profiles of wind and temperature. The 80 % availability of the WPR/RASS was determined with 12.8 km for wind and 2.3 km for temperature measurements. The new possibilities of investigating the troposphere as well as the lowest part of the stratosphere are presented by measurement examples from February and March 1997. more...
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- 1998
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10. Breakthrough Invasive Fusarium Orbital Rhinosinusitis With Meningitis.
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Tawfiq RK, Ranganath N, Lehman V, Yin LX, and Schuetz AN
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- Humans, Fusarium, Meningitis, Rhinitis complications, Rhinitis diagnosis, Sinusitis complications, Sinusitis diagnosis
- Published
- 2022
- Full Text
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11. Decreased vessel wall enhancement as a biomarker for response to corticosteroids in a patient with CNS vasculitis.
- Author
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Brinjikji W, Lehman V, Huston J 3rd, Luetmer PH, Lanzino G, and Rabinstein AA
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- Biomarkers, Female, Humans, Magnetic Resonance Angiography, Middle Aged, Neurosurgical Procedures, Vascular Surgical Procedures, Adrenal Cortex Hormones pharmacology, Vasculitis, Central Nervous System diagnostic imaging, Vasculitis, Central Nervous System drug therapy, Vasculitis, Central Nervous System surgery
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- 2019
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12. Vessel Wall Imaging of Intracranial Aneurysms: Systematic Review and Meta-analysis.
- Author
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Texakalidis P, Hilditch CA, Lehman V, Lanzino G, Pereira VM, and Brinjikji W
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- Brain blood supply, Brain diagnostic imaging, Humans, Observational Studies as Topic, Blood Vessels diagnostic imaging, Intracranial Aneurysm diagnostic imaging
- Abstract
Vessel wall imaging (VWI) is emerging as a novel imaging tool for the management and risk stratification of patients with intracranial saccular aneurysms. Our objective was to compare the rates of wall enhancement in unstable (ruptured, growing, or symptomatic) and stable aneurysms and assess the ability of VWI with high-resolution magnetic resonance imaging to distinguish between these 2 entities. This study was performed according to Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines, and eligible studies were identified through a comprehensive literature review. A meta-analysis was conducted to examine the association between aneurysm wall enhancement and aneurysm instability with the use of a random effects model. The I
2 statistic was used to assess for heterogeneity. Six studies comprising 505 saccular aneurysms were included. Aneurysms that showed vessel wall enhancement had statistically significant higher odds of being unstable (odds ratio [OR]: 20; 95% confidence interval [CI]: 6.4-62.1; I2 : 63.1%). The sensitivity, specificity, positive predictive value, and negative predictive value of VWI in identifying unstable aneurysms were 95.0% (90.4-97.8), 62.7% (57.1-67.9), 55.8% (52.2-59.4), and 96.2% (92.8-98.0), respectively. There is a statistically significant association between vessel wall enhancement and aneurysm instability. Importantly, the lack of wall enhancement is a strong predictor of aneurysm stability. VWI could potentially provide new insights in the management of intracranial aneurysms., (Copyright © 2018 Elsevier Inc. All rights reserved.) more...- Published
- 2018
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13. Intracranial and Extracranial Neurovascular Manifestations of Takayasu Arteritis.
- Author
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Bond KM, Nasr D, Lehman V, Lanzino G, Cloft HJ, and Brinjikji W
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- Adult, Carotid Stenosis diagnostic imaging, Cerebral Hemorrhage diagnostic imaging, Cerebral Infarction diagnostic imaging, Constriction, Pathologic, Dizziness etiology, Female, Headache etiology, Humans, Intracranial Aneurysm diagnostic imaging, Magnetic Resonance Imaging, Male, Middle Aged, Subclavian Steal Syndrome diagnostic imaging, Takayasu Arteritis pathology, Vasculitis, Central Nervous System diagnostic imaging, Young Adult, Blood Vessels pathology, Nervous System pathology, Takayasu Arteritis complications
- Abstract
Background and Purpose: Takayasu arteritis is a rare, large-vessel vasculitis that presents with symptoms related to end-organ ischemia. While the extracranial neurovascular manifestations of Takayasu arteritis are well-established, little is known regarding the intracranial manifestations. In this study, we characterize the intracranial and cervical neurovascular radiologic findings in patients with Takayasu arteritis., Materials and Methods: Patients with Takayasu arteritis who presented to our institution between 2001 and 2016 with intracranial and/or cervical vascular imaging were included in this study. Images were evaluated for the presence of vascular abnormalities, including intracranial or extracranial stenosis, vessel-wall thickening, dissection, subclavian steal, aneurysms, infarcts, and hemorrhages. Descriptive analyses are reported., Results: Seventy-nine patients with Takayasu arteritis met the criteria for inclusion in this study. The most common presenting neurologic symptoms were headache (32.9%) and dizziness (15.2%). Intracranial and extracranial vascular imaging was performed in 84.8% and 89.9% of patients, respectively. Among patients with intracranial vascular imaging, 3 (3.9%) had intracranial aneurysms, 3 (3.9%) had acute large-vessel occlusion, 6 (7.6%) had intracranial vasculitis, and 1 (1.3%) had reversible cerebrovascular constriction syndrome. Among patients with cervical vascular imaging, 42 (53.1%) had some degree of narrowing of the common carotid artery and 18 (22.8%) had narrowing of the ICAs. Seventeen patients (23.6%) had subclavian steal., Conclusions: Intracranial vascular abnormalities in patients with Takayasu arteritis presenting with neurologic symptoms are not rare, with cerebral vasculitis seen in 7.8% of patients, and stroke secondary to large-vessel occlusion, in 3.9% of patients. Cervical vascular manifestations of Takayasu arteritis were present in most patients in our study., (© 2017 by American Journal of Neuroradiology.) more...
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- 2017
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14. A practice audit of CT-guided injections of pars interarticularis defects in patients with axial low back pain: a primer for further investigation.
- Author
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Wald JT, Geske JR, Diehn FE, Murthy NS, Kaufmann TJ, Thielen KR, Morris JM, Lehman VT, and Maus TP
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- Adult, Chronic Pain diagnostic imaging, Chronic Pain drug therapy, Female, Follow-Up Studies, Humans, Injections, Intralesional methods, Male, Medical Audit, Middle Aged, Pilot Projects, Retrospective Studies, Treatment Outcome, Young Adult, Adrenal Cortex Hormones administration & dosage, Anesthetics, Local administration & dosage, Low Back Pain diagnostic imaging, Low Back Pain drug therapy, Lumbar Vertebrae diagnostic imaging, Tomography, X-Ray Computed methods
- Abstract
Objective: To assess whether computed tomography (CT)-guided injections of local anesthetic and corticosteroid into chronic lumbar pars interarticularis defects may identify and provide benefit to a cohort of patients where the pars defects act as a primary axial pain generator., Design: Retrospective practice audit., Setting: Single academic radiology pain management practice., Patients: 59 consecutive patients undergoing CT-guided injections of lumbar pars defects., Methods: Patients were assessed with a pain numerical rating scale (NRS, 0-10) and Roland-Morris disability questionnaire (R-M) prior to injection and at 2 weeks and 2 months follow-up. For categorical outcomes, successful pain relief response was defined as either ≥50% reduction in NRS or pain 0/10; functional response was defined as ≥40% reduction in R-M score. Continuous outcomes (mean NRS, R-M scores) were assessed for significant change following injection., Results: For categorical outcomes, 37.9% of patients were responders at 2 months' follow-up; 20.7 % had complete relief of index pain. For functional recovery, 34.5% were responders at 2 months. Using continuous outcomes, mean NRS was 5.4 ± 2.1 prior to injection and 3.6 ± 2.6 at 2 months (P < 0.0001). Mean R-M score was 11.7 ± 6.0 prior to injection and 9.0 ± 5.4 at 2 months (P = 0.001). There were no complications., Conclusions: This practice audit suggests that in patients with axial low back pain and chronic pars defects, the pars defects may be implicated as the primary axial pain generator in a small subgroup of patients. Local deposition of corticosteroids into the pars defect may provide significant pain relief in one out of three patients, and complete relief in one out of five patients. This data suggest there may be benefit to pursuing randomized controlled trials of pars injections comparing steroid injection with placebo., (Wiley Periodicals, Inc.) more...
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- 2014
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15. A group home--hospital treatment model for severely disturbed adolescents.
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Hoffmann LR, Lehman V, and Zev ED
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- Adolescent, Aftercare, Education, Special, Evaluation Studies as Topic, Female, Group Processes, Humans, Male, New York City, Social Adjustment, Adolescent Psychiatry, Affective Symptoms rehabilitation, Halfway Houses, Hospitals, Psychiatric
- Published
- 1975
16. [Letter: Discomfort in school children].
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Lehman V
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- Norway, School Health Services, Social Adjustment
- Published
- 1976
17. Leukolytic activity of Acinetobacter calcoaceticus.
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Lehman V and Wiig JN
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- Alcaligenes enzymology, Animals, Culture Media, Dye Dilution Technique, Edetic Acid pharmacology, Electrophoresis, Female, Hot Temperature, Hydrogen-Ion Concentration, Magnesium pharmacology, Male, Methods, Mice, Phospholipases analysis, Thymus Gland cytology, Alcaligenes drug effects, Hemolysin Proteins, Hemolysis, T-Lymphocytes drug effects
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- 1972
- Full Text
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