Science.gov

Sample records for 16-slice spiral ct

  1. Cone-angle-dependent generalized weighting scheme for 16-slice helical CT

    NASA Astrophysics Data System (ADS)

    Hsieh, Jiang; Dong, Yanting; Simoni, Piero; Toth, Thomas; Slack, Christopher L.; Grekowicz, Brian; Seidenschnur, George; Shaughnessy, Charlie

    2002-05-01

    Since the recent introduction of multi-slice helical computed tomography (MHCT), new clinical applications have experienced tremendous growth in recent years. MHCT offers improved volume coverage, faster scan speed, more isotropic spatial resolution, and reduced x-ray tube loading. Similar to the single slice helical CT, the projection data collected in MHCT is inherently inconsistent due to the constant table motion. In addition, cone beam effects in MHCT produce additional complexity and image artifacts. Although the cone angle is quite smaller even for the 16-slice configuration, the impact on image artifacts cannot be ignored. Many reconstruction algorithms have been proposed and investigated recently to combat image artifacts associated with the MHCT data acquisition. In this paper, we propose a cone-angle dependent generalized weighting scheme for 16-slice helical CT that allows the production of MHCT images with only 2D backprojection. The cone-angle dependency of the algorithm suppresses image artifacts due to the cone beam effect and the generalized weighting portion enables interpolation be performed with conjugate samples for the 16-slice helical dataset. With the proposed algorithm, image artifacts are significantly reduced.

  2. Clinical use of multislice spiral computed tomography in 210 highly preselected patients: experience with 4 and 16 slice technology

    PubMed Central

    Beck, T; Burgstahler, C; Kuettner, A; Kopp, A F; Heuschmid, M; Claussen, C D; Schroeder, S

    2005-01-01

    Objective: To report an initial experience with multislice spiral computed tomography (MSCT) coronary imaging, as well as differences in diagnostic accuracy between 4 slice and 16 slice MSCT technology. Methods and results: 210 patients underwent MSCT coronary angiography (4 slices, n  =  120; 16 slices, n  =  90; suspicion of coronary artery disease, n  =  158; suspicion of restenosis, n  =  52). Recommendations for further diagnostic tests were based on the MSCT results. Patients were interviewed by telephone after a mean (SD) of 449 (169) days to evaluate their further clinical course. MSCT detected significant lesions in 90 of 210 (43%) patients and invasive coronary angiography (ICA) was recommended. MSCT excluded significant lesions in 120 of 210 (57%) patients. ICA was actually performed in 44 of 210 (21%) patients (corresponding results, 27 of 44 (61%); false positive, 11 of 44 (25%); false negative, 6 of 44 (14%)). No significant differences were found between 4 and 16 slice imaging. No major cardiac event occurred during follow up. Conclusions: MSCT was found to be useful to evaluate the need for invasive diagnostic procedures. However, the false negative results underline that further improvements of image quality are required before MSCT can replace ICA in carefully selected patients. PMID:15761053

  3. Spiral CT: vascular applications.

    PubMed

    Rankin, S C

    1998-08-01

    Recent technical advances in CT have renewed interest in the development of CT angiography (CTA). CT angiography is a minimally invasive method of visualising the vascular system and is becoming an alternative to conventional arteriography in some situations. Spiral technology allows a volume of data to be obtained on a single breath-hold with no respiratory misregistration. Fast machines with second or subsecond acquisition times mean the images are obtained while there are high circulating levels of contrast medium giving peak vascular opacification from a peripheral intravenous injection. Accurate timing will ensure either the arterial or venous phase is imaged. Multiple overlapping axial images can be obtained from the data set with no increase in radiation dose to the patient and from these scans computer generated multiplanar and 3D images are obtained which can be viewed from numerous angles. CT angiography can be performed more quickly, less invasively and at reduced cost compared to conventional angiography. PMID:9717621

  4. Spiral CT image deblurring for cochlear implantation.

    PubMed

    Wang, G; Vannier, M W; Skinner, M W; Cavalcanti, M G; Harding, G W

    1998-04-01

    Cochlear implantation is the standard treatment for profound hearing loss. Preimplantation and postimplantation spiral computed tomography (CT) is essential in several key clinical and research aspects. The maximum image resolution with commercial spiral CT scanners is insufficient to define clearly anatomical features and implant electrode positions in the inner ear. In this paper, we develop an expectation-maximization (EM)-like iterative deblurring algorithm to achieve spiral CT image super-resolution for cochlear implantation, assuming a spatially invariant linear spiral CT system with a three-dimensional (3-D) separable Gaussian point spread function (PSF). We experimentally validate the 3-D Gaussian blurring model via phantom measurement and profile fitting. The imaging process is further expressed as convolution of an isotropic 3-D Gaussian PSF and a blurred underlying volumetric image. Under practical conditions, an oblique reconstructed section is approximated as convolution of an isotropic two-dimensional (2-D) Gaussian PSF and the corresponding actual cross section. The spiral CT image deblurring algorithm is formulated with sieve and resolution kernels for suppressing noise and edge artifacts. A typical cochlear cross section is used for evaluation, demonstrating a resolution gain up to 30%40% according to the correlation criterion. Physical phantoms, preimplantation and postimplantation patients are reconstructed into volumes of 0.1-mm cubic voxels. The patient images are digitally unwrapped along the central axis of the cochlea and the implanted electrode array respectively, then oblique sections orthogonal to the central axis formed. After deblurring, representation of structural features is substantially improved in all the cases. PMID:9688157

  5. Effect of pitch in multislice spiral/helical CT

    NASA Astrophysics Data System (ADS)

    Wang, Ge; Vannier, Michael W.

    1999-09-01

    To understand the effect of pitch on raw data interpolation in multi-slice spiral/helical CT, and provide guidelines for scanner design and protocol optimization. Multi-slice spiral CT is mainly characterized by the three parameters: the number of detector arrays, the detector collimation, and the table increment per X-ray source rotation. The pitch in multi-slice spiral CT is defined as the ratio of the table increment over the detector collimation. In parallel to the current framework for studying longitudinal image resolution, the central fan- beam rays of direct and opposite directions are considered, assuming a narrow cone-beam angle. Generally speaking, sampling in the Radon domain by the direct and opposite central rays is non-uniform along the longitudinal axis. Using a recently developed methodology for quantifying the sensitivity of signal reconstruction from non-uniformly sampled finite points, the effect of pitch on raw data interpolation is analyzed in multi-slice spiral CT. Unlike single-slice spiral CT, in which image quality deceases monotonically as the pitch increases, the sensitivity of raw data interpolation in multi-slice spiral CT increases in an alternating way as the pitch increases, suggesting that image quality does not decrease monotonically in this case. The most favorable pitch can be found from the sensitivity-pitch plot for any given set of multi-slice spiral CT parameters. An example for four-slice spiral CT is provided. The study on the pitch effect using the sensitivity analysis approach reveals the fundamental characteristics of raw data interpolation in multi-slice spiral CT, and gives insights into interaction between pitch and image quality. These results may be valuable for design of multi-slice spiral CT scanners and imaging protocol optimization in clinical applications.

  6. The feasibility of a 64-slice MDCT for detection of the Adamkiewicz artery: comparison of the detection rate of intravenous injection CT angiography using a 64-slice MDCT versus intra-arterial and intravenous injection CT angiography using a 16-slice MDCT.

    PubMed

    Nishii, Tatsuya; Kono, Atsushi K; Negi, Noriyuki; Hashimura, Hiromi; Uotani, Kensuke; Okita, Yutaka; Sugimura, Kazuro

    2013-12-01

    Identification of the Adamkiewicz artery (AKA) using CT angiography (CTA) is crucial in patients with thoracic aortic aneurysm (TAA) or aortic dissection (AD). The purpose of this study was to compare the AKA detection rate of intravenous injection with a 64-slice MDCT (IV64) versus a 16-slice MDCT (IV16) as well as by CTA using intra-arterial injection with a 16-slice MDCT (IA16). A retrospective review of 160 consecutive patients who underwent CTA was performed. There were 108 TAA and 52 AD cases, 105 of whom were examined with IV64, 15 with IV16, and 40 with IA16. The AKA detectability for each imaging method was assessed, and the factors influencing the detectability were analyzed by multivariate analysis. The detection rates for IV64, IV16, and IA16 were 85.7, 60.0, and 80.0 %, respectively, with IV64 being more sensitive than IV16 (P = 0.025). The detection rate for AD patients was 66.7 % with IV64, which was similar to IV16 (57.1 %) and IA16 (66.8 %). On the other hand, the detection rate for TAA patients was 93.3 % with IV64, which was higher than IV16 (62.5 %, P = 0.021) and similar to IA16 (88.0 %). Multivariate analysis demonstrated the independent factors for AKA detectability were TAA versus AD (P = 0.005, Odds ratio = 3.98) and IV64 versus IV16 (P = 0.037, Odds ratio = 4.03). The detection rate was higher for IV64 than for IV16, especially for TAA patients, while the rate was similar between IV64 and invasive IA16. A 64-slice MDCT thus provides a less invasive visualization of the AKA. PMID:24081485

  7. [Cerebral aneurysms: their 3-dimensional imaging with spiral CT].

    PubMed

    Rieger, J; Hosten, N; Lemke, A J; Langer, R; Lanksch, W R; Felix, R

    1994-03-01

    In this study, the possibility of non-invasive, three-dimensional demonstration of aneurysms of the basal cerebral arteries by means of spiral CT was investigated. The first step was to obtain exact definition of optimal examination parameters. Angio CTs at appropriate levels were performed on 10 subjects and time/density curves of the arterial and venous phases obtained in order to optimise the beginning of the arterial spiral CT series. The second step in this investigation was to examine 7 patients; in 6 of these basal aneurysms had been demonstrated by DSA. By means of multiplanar three-dimensional reconstruction from the data of the spiral CT it was possible to demonstrate 7 aneurysms with a diameter between 5 and 18 mm. Their position and relationship to the bony skull was also shown. PMID:8136472

  8. Three-dimensional dental imaging by spiral CT

    NASA Astrophysics Data System (ADS)

    Vannier, Michael W.; Hildebolt, Charles F.; Conover, Gary; Knapp, Robert H.; Yokoyama-Crothers, Naoko; Wang, Ge

    1995-05-01

    Three-dimensional image acquisition, display, and analysis of dental structures was performed and validated using spiral computed tomography (SCT) with metal artifact suppression. Isolated extracted teeth, a dry mandible, cadaver mandible, and cadaver head were scanned and reconstructed using a spiral CT scanner (Siemens Somatom PLUS-S) with 1 mm detector collimation, 1-mm table feed, and 0.1 - 1 mm reconstruction interval using specially developed software. Algorithms for metal artifact reduction including extended attenuation range and interpolation of missing projections were applied. Volumetric rendering of voxel sum images was performed to synthesize images comparable to conventional intraoral dental radiographs. Direct comparison of voxel-based synthetic and digitized film images was made. Several isolated, extracted teeth were sectioned with a diamond saw and submitted for histomorphometric analysis to aid in direct comparison with CT slice images obtained by multiplanar reconstruction. Metal artifact reduction was successful in markedly reducing the streaks and star patterns that usually accompany metallic restorations and intraoral appliances. Individual teeth were comparable to CT slice images. Voxel sum images were comparable to dental radiographs; however, for the SCT images, the spatial resolution was higher within the plane of section than it was orthogonal to the plane of section. Serial examinations were obtained by SCT, registered by surface matching, and interval change measured by 3D subtraction. Simulated lesions and restorations were introduced and quantitatively evaluated pre- and post-interventionally to assess imaging method performance.

  9. Three-dimensional spiral CT for craniofacial surgical planning and evaluation

    NASA Astrophysics Data System (ADS)

    Cavalcanti, Marcelo G.; Vannier, Michael W.

    1998-06-01

    Purpose: To evaluate measurement accuracy of 3D volumetric medical imaging from Spiral CT for craniofacial surgical planing. Material and methods: The study population consisted of 5 cadaver heads that were imaged on a spiral CT scanner with volumetric technique high-resolution contiguous axial slices 3mm thickness and 2mm/sec table feed, with 120Kvp and 200 mA. The archived CT data were stored on optical disks to allow full retrospective review of any image. The data sets were transferred to a networked computer workstation, to generated 3D volumetric images for subsequent manipulation and analyses. The computer graphics workstation allowed to do measurements, based on conventional craniometric anatomic landmarks, by 2 observers with 2 sessions each. The specimens were then submitted to a dynamic blunt force, in an effort to simulate craniofacial fractures, scanned and measured again. The soft tissues were then partially subsequently removed and the measurements were repeated by electromagnetic digitizer. Statistical analysis was done using analysis of variance. Results: Measurements from 3D spiral CT scans can be precise with high repeatability and sufficient accuracy for surgical planing. Conclusion: 3D computer graphics by spiral CT allowed, in vitro, sufficient precision for assessment of surgical management. Digital volumetric spiral CT imaging is valid quantitatively and qualitatively for craniofacial surgical planning and evaluation.

  10. High-pitch spiral acquisition: a new scan mode for coronary CT angiography.

    PubMed

    Achenbach, Stephan; Marwan, Mohamed; Schepis, Tiziano; Pflederer, Tobias; Bruder, Herbert; Allmendinger, Thomas; Petersilka, Martin; Anders, Katharina; Lell, Michael; Kuettner, Axel; Ropers, Dieter; Daniel, Werner G; Flohr, Thomas

    2009-01-01

    Coronary CT angiography allows high-quality imaging of the coronary arteries when state-of-the-art CT systems are used. However, radiation exposure has been a concern. We describe a new scan mode that uses a very high-pitch spiral acquisition, "Flash Spiral," which has been developed specifically for low-dose imaging with dual-source CT. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set, while covering the entire volume of the heart in one cardiac cycle. Data acquisition is prospectively triggered by the electrocardiogram and starts in late systole to be completed within one cardiac cycle. Images are reconstructed with a temporal resolution that corresponds to one-quarter of the gantry rotation time. Throughout the data set, subsequent images are reconstructed at later time instants in the cardiac cycle. In a patient with a heart rate of 49 beats/min, the Flash Spiral scan mode was used with a first-generation dual-source CT system and allowed artifact-free visualization of the coronary arteries with a radiation exposure of 1.7 mSv for a 12-cm scan range at 120 kVp tube voltage. PMID:19332343

  11. [Small renal cell carcinoma (≤ 4 cm): enhancement patterns on triphasic spiral CT].

    PubMed

    Rebonato, Alberto; Pierotti, Luisa; Barberini, Francesco; Rosi, Giovanni; Macarini, Luca; Scialpi, Michele

    2012-11-01

    The aim of this study was to define enhancement patterns of small renal cell carcinoma (RCC) (≤4 cm) by triphasic spiral CT. In 24 patients with RCC, hypervascularity and hypovascularity were identified in 12 and 12 RO, respectively, in the cortico-medullary phase (CMP). Hypervascular RCC showed increased density in the CMP (170,7±46,3 UH) and a gradual wash-out in the nephrographic phase (NP) (152,5±41 UH) and pielographic phase (PF) (99,2±38 UH). Hypovascular RCC showed increased density in the CMP (52,9±24,7 UH) and a gradual wash-out in NP (64,5±16,9 UH) and PP phases (55,0±17,3 UH). PMID:23096734

  12. Reproducibility of the coronary calcium measurement with different cardiac algorithms using multislice spiral CT

    NASA Astrophysics Data System (ADS)

    Liang, Yun; Krishnamurthi, Ganapathy; Chen, Laigao M.; Meyer, Cristopher A.

    2002-05-01

    Subsecond multi-slice spiral CT has now been recognized with its great potential in cardiac imaging, in particularly for the coronary calcification detection (CCD). Different reconstruction algorithms have been developed in order to optimize the temporal resolution and to improve the measurement accuracy. These algorithms typically incorporate retrospectively gated reconstructions based on a synchronized electrocardiography (ECG) recording. However, these algorithms consist of different approaches in choosing spatial filters, setting ECG delays, and employing the reconstruction geometry (direct fan-beam vs. parallel rebining). These differences are likely to contribute to the intrascanner and interscanner variability in the coronary calcium measurements. This paper investigates in detail about the quantitative effect on calcium detection among different approaches.

  13. Detection, visualization and evaluation of anomalous coronary anatomy on 16-slice multidetector-row CT.

    PubMed

    van Ooijen, Peter M A; Dorgelo, Joost; Zijlstra, Felix; Oudkerk, Matthijs

    2004-12-01

    Early identification and evaluation of relatively frequent anomalous coronary anatomy is quite relevant because of the occurrence of sudden cardiac death or related symptoms of myocardial ischemia. Selective coronary angiography (CAG) is invasive, expensive and cannot always provide the required information adequately. Recently, non-invasive imaging techniques such as magnetic resonance imaging and multidetector-row computed tomography (MDCT) have been shown to provide a good anatomical view of the coronary artery tree. This study aims to demonstrate the value of 16-MDCT for evaluation of anomalous coronary anatomy. In 13 patients scanned using 16-MDCT, six different coronary anomalies were diagnosed [two absent left main, one single vessel left coronary artery (LCA), three LCA originating from the right (two with interarterial course), six right coronary artery originating from the left, one double left anterior descending (LAD)]. Mean diagnostic quality, recorded by two observers using a 5-point scale (1= non-diagnostic to 5= excellent diagnostic quality), resulted in a mean score of 3.73 (SD 1.19) without any non-diagnostic result. MDCT offers an accurate diagnostic modality to visualize the origin and course of anomalous coronary arteries by a three-dimensional display of anatomy. Shortcomings in CAG can be overcome by the use of contrast-enhanced MDCT. PMID:15452665

  14. Comparison of fan-beam, cone-beam, and spiral scan reconstruction in x-ray micro-CT

    NASA Astrophysics Data System (ADS)

    Sasov, Alexander

    2001-06-01

    We developed and tested reconstruction software packages for different algorithms: fan-beam, cone-beam (Feldkamp) and spiral (helical) scans. All algorithms were applied to different simulations as well as to the real datasets from the commercial micro-CT instruments. From the results of testing a number of strong and weak points at different approaches was found. Several examples from the different application areas (bone microstructure, industrial applications) show typical reconstruction artifacts with different algorithms.

  15. Quantitative parameters to compare image quality of non-invasive coronary angiography with 16-slice, 64-slice and dual-source computed tomography.

    PubMed

    Burgstahler, Christof; Reimann, Anja; Brodoefel, Harald; Daferner, Ulrike; Herberts, Tina; Tsiflikas, Ilias; Thomas, Christoph; Drosch, Tanja; Schroeder, Stephen; Heuschmid, Martin

    2009-03-01

    Multi-slice computed tomography (MSCT) is a non-invasive modality to visualize coronary arteries with an overall good image quality. Improved spatial and temporal resolution of 64-slice and dual-source computed tomography (DSCT) scanners are supposed to have a positive impact on diagnostic accuracy and image quality. However, quantitative parameters to compare image quality of 16-slice, 64-slice MSCT and DSCT are missing. A total of 256 CT examinations were evaluated (Siemens, Sensation 16: n = 90; Siemens Sensation 64: n = 91; Siemens Definition: n = 75). Mean Hounsfield units (HU) were measured in the cavum of the left ventricle (LV), the ascending aorta (Ao), the left ventricular myocardium (My) and the proximal part of the left main (LM), the left anterior descending artery (LAD), the right coronary artery (RCA) and the circumflex artery (CX). Moreover, the ratio of intraluminal attenuation (HU) to myocardial attenuation was assessed for all coronary arteries. Clinical data [body mass index (BMI), gender, heart rate] were accessible for all patients. Mean attenuation (CA) of the coronary arteries was significantly higher for DSCT in comparison to 64- and 16-slice MSCT within the RCA [347 +/- 13 vs. 254 +/- 14 (64-MSCT) vs. 233 +/- 11 (16-MSCT) HU], LM (362 +/- 11/275 +/- 12/262 +/- 9), LAD (332 +/- 17/248 +/- 19/219 +/- 14) and LCX (310 +/- 12/210 +/- 13/221 +/- 10, all p < 0.05), whereas there was no significant difference between DSCT and 64-MSCT for the LV, the Ao and My. Heart rate had a significant impact on CA ratio in 16-slice and 64-slice CT only (p < 0.05). BMI had no impact on the CA ratio in DSCT only (p < 0.001). Improved spatial and temporal resolution of dual-source CT is associated with better opacification of the coronary arteries and a better contrast with the myocardium, which is independent of heart rate. In comparison to MSCT, opacification of the coronary arteries at DSCT is not affected by BMI. The main advantage of DSCT lies with the

  16. Spiral CT During Selective Accessory Renal Artery Angiography: Assessment of Vascular Territory Before Aortic Stent-Grafting

    SciTech Connect

    Dorffner, Roland; Thurnher, Siegfried; Prokesch, Rupert; Youssefzadeh, Soraya; Hoelzenbein, Thomas; Lammer, Johannes

    1998-03-15

    We evaluated the vascular territory of accessory renal arteries in cases where the vessel might be overlapped by an aortic stent-graft. Spiral CT during selective accessory renal artery angiography was performed in four patients with abdominal aortic aneurysms (including one with a horseshoe kidney). The volume of the vascular territory of each renal artery was measured using a software program provided by the CT unit manufacturer. The supernumerary renal arteries perfused 32%, 37%, 15%, and 16% of the total renal mass, respectively. In two patients, stent-grafts were implanted, which resulted in occlusion of the supernumerary renal artery. The volume of the renal infarction was equal to the volume perfused by the artery as calculated before implantation of the stent-graft.The method proposed is accurate for estimating the size of the expected renal infarction. It might help to determine whether placement of a stent-graft is acceptable.

  17. Image Quality of 3rd Generation Spiral Cranial Dual-Source CT in Combination with an Advanced Model Iterative Reconstruction Technique: A Prospective Intra-Individual Comparison Study to Standard Sequential Cranial CT Using Identical Radiation Dose

    PubMed Central

    Wenz, Holger; Maros, Máté E.; Meyer, Mathias; Förster, Alex; Haubenreisser, Holger; Kurth, Stefan; Schoenberg, Stefan O.; Flohr, Thomas; Leidecker, Christianne; Groden, Christoph; Scharf, Johann; Henzler, Thomas

    2015-01-01

    Objectives To prospectively intra-individually compare image quality of a 3rd generation Dual-Source-CT (DSCT) spiral cranial CT (cCT) to a sequential 4-slice Multi-Slice-CT (MSCT) while maintaining identical intra-individual radiation dose levels. Methods 35 patients, who had a non-contrast enhanced sequential cCT examination on a 4-slice MDCT within the past 12 months, underwent a spiral cCT scan on a 3rd generation DSCT. CTDIvol identical to initial 4-slice MDCT was applied. Data was reconstructed using filtered backward projection (FBP) and 3rd-generation iterative reconstruction (IR) algorithm at 5 different IR strength levels. Two neuroradiologists independently evaluated subjective image quality using a 4-point Likert-scale and objective image quality was assessed in white matter and nucleus caudatus with signal-to-noise ratios (SNR) being subsequently calculated. Results Subjective image quality of all spiral cCT datasets was rated significantly higher compared to the 4-slice MDCT sequential acquisitions (p<0.05). Mean SNR was significantly higher in all spiral compared to sequential cCT datasets with mean SNR improvement of 61.65% (p*Bonferroni0.05<0.0024). Subjective image quality improved with increasing IR levels. Conclusion Combination of 3rd-generation DSCT spiral cCT with an advanced model IR technique significantly improves subjective and objective image quality compared to a standard sequential cCT acquisition acquired at identical dose levels. PMID:26288186

  18. Segmentation of pulmonary nodules in three-dimensional CT images by use of a spiral-scanning technique

    SciTech Connect

    Wang Jiahui; Engelmann, Roger; Li Qiang

    2007-12-15

    Accurate segmentation of pulmonary nodules in computed tomography (CT) is an important and difficult task for computer-aided diagnosis of lung cancer. Therefore, the authors developed a novel automated method for accurate segmentation of nodules in three-dimensional (3D) CT. First, a volume of interest (VOI) was determined at the location of a nodule. To simplify nodule segmentation, the 3D VOI was transformed into a two-dimensional (2D) image by use of a key 'spiral-scanning' technique, in which a number of radial lines originating from the center of the VOI spirally scanned the VOI from the 'north pole' to the 'south pole'. The voxels scanned by the radial lines provided a transformed 2D image. Because the surface of a nodule in the 3D image became a curve in the transformed 2D image, the spiral-scanning technique considerably simplified the segmentation method and enabled reliable segmentation results to be obtained. A dynamic programming technique was employed to delineate the 'optimal' outline of a nodule in the 2D image, which corresponded to the surface of the nodule in the 3D image. The optimal outline was then transformed back into 3D image space to provide the surface of the nodule. An overlap between nodule regions provided by computer and by the radiologists was employed as a performance metric for evaluating the segmentation method. The database included two Lung Imaging Database Consortium (LIDC) data sets that contained 23 and 86 CT scans, respectively, with 23 and 73 nodules that were 3 mm or larger in diameter. For the two data sets, six and four radiologists manually delineated the outlines of the nodules as reference standards in a performance evaluation for nodule segmentation. The segmentation method was trained on the first and was tested on the second LIDC data sets. The mean overlap values were 66% and 64% for the nodules in the first and second LIDC data sets, respectively, which represented a higher performance level than those of two

  19. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion

    PubMed Central

    Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D.; Ramsay, Jason B.; Schlader, Robert; Didier, Dominique A.

    2013-01-01

    New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays. PMID:23445952

  20. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion.

    PubMed

    Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D; Ramsay, Jason B; Schlader, Robert; Didier, Dominique A

    2013-04-23

    New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays. PMID:23445952

  1. Incidental finding of a papillary fibroelastoma on the aortic valve in 16 slice multi-detector row computed tomography.

    PubMed

    Bootsveld, A; Puetz, J; Grube, E

    2004-06-01

    Papillary fibroelastoma (PFE) is a benign, rare, gelatinous tumour derived from the endocardium, primarily the cardiac valves, which is usually diagnosed by high resolution echocardiography. Although rarely clinically symptomatic, PFEs have a potential for coronary ischaemia, systemic embolisation with neurologic symptoms, and sometimes valvar dysfunction. There are reports of coronary occlusion and even sudden cardiac death due to a ball valve phenomenon on the coronary ostia. This report describes the characteristics of a PFE with multidetector 16 slice computed tomography and 1.5 Tesla cardiac magnetic resonance imaging. PMID:15145899

  2. Impact of the z-flying focal spot on resolution and artifact behavior for a 64-slice spiral CT scanner.

    PubMed

    Kyriakou, Yiannis; Kachelriess, Marc; Knaup, Michael; Krause, Jens U; Kalender, Willi A

    2006-06-01

    The effect of the z-flying focal spot (zFFS) technology was evaluated by simulations and measurements with respect to resolution and artifact behavior for a 64-slice spiral cone-beam computed tomography (CT) scanner. The zFFS alternates between two z-positions of the X-ray focal spot, acquiring two slices per detector row, which results in double sampling in the z-direction. We implemented a modified reconstruction that is able to obtain images as they would be without zFFS. A delta phantom equipped with a thin gold disc was used to measure slice sensitivity profiles (SSP), and a high-contrast bar phantom was used to quantify the resolution in the x/z-plane with and without zFFS. The zFFS decreases the full width at half maximum (FWHM) of the SSPs by a factor of about 1.4. The double z-sampling allows the separation of 0.4 mm bars in the z-direction compared with 0.6 mm in the case without zFFS. The zFFS effectively reduces windmill artifacts in the reconstructed images while maintaining the transverse resolution, even at the largest available pitch value of 1.5. PMID:16541229

  3. Spiral CT Quantification of Aorto-Renal Calcification and Its Use in the Detection of Atheromatous Renal Artery Stenosis: A Study in 42 Patients

    SciTech Connect

    Gayard, Pierre; Garcier, Jean-Marc; Boire, Jean-Yves; Ravel, Anne; Perez, Nessim; Privat, Christian; Lucien, Pascal; Viallet, Jean-Francois; Boyer, Louis

    2000-01-15

    Purpose: To investigate whether a correlation exists between aortic and renal arterial calcifications detected with spiral CT and significant angiographic renal artery stenosis (RAS).Methods: Forty-two patients (mean age 67 years, range 37-84 years), of whom 24 were hypertensive, prospectively underwent abdominal helical CT and aortic and renal arteriography. The 3-mm thickness CT scans (pitch = 1) were reconstructed each millimeter. A manual outline of the renal artery including its ostial portion was produced. Calcific hyperdensities were defined as areas of density more than 130 HU. CT data were compared with the presence or absence of RAS on angiography (24 cases); hypertension and age were taken into account (Mann-Whitney U-test).Results: CT detection and quantification appeared to be reliable and reproductible. We did not find any correlation between aortic and renal arterial calcifications and RAS, even for the patients above 65 years, with or without hypertension. There was no correlation either between calcifications and hypertension in patients without RAS. Conclusion: In this population, aortic and renal arterial calcifications have no predictive value for RAS.

  4. Dual-source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: Image reconstruction and assessment of image quality

    SciTech Connect

    Flohr, Thomas G.; Leng Shuai; Yu Lifeng; Allmendinger, Thomas; Bruder, Herbert; Petersilka, Martin; Eusemann, Christian D.; Stierstorfer, Karl; Schmidt, Bernhard; McCollough, Cynthia H.

    2009-12-15

    Purpose: To present the theory for image reconstruction of a high-pitch, high-temporal-resolution spiral scan mode for dual-source CT (DSCT) and evaluate its image quality and dose. Methods: With the use of two x-ray sources and two data acquisition systems, spiral CT exams having a nominal temporal resolution per image of up to one-quarter of the gantry rotation time can be acquired using pitch values up to 3.2. The scan field of view (SFOV) for this mode, however, is limited to the SFOV of the second detector as a maximum, depending on the pitch. Spatial and low contrast resolution, image uniformity and noise, CT number accuracy and linearity, and radiation dose were assessed using the ACR CT accreditation phantom, a 30 cm diameter cylindrical water phantom or a 32 cm diameter cylindrical PMMA CTDI phantom. Slice sensitivity profiles (SSPs) were measured for different nominal slice thicknesses, and an anthropomorphic phantom was used to assess image artifacts. Results were compared between single-source scans at pitch=1.0 and dual-source scans at pitch=3.2. In addition, image quality and temporal resolution of an ECG-triggered version of the DSCT high-pitch spiral scan mode were evaluated with a moving coronary artery phantom, and radiation dose was assessed in comparison with other existing cardiac scan techniques. Results: No significant differences in quantitative measures of image quality were found between single-source scans at pitch=1.0 and dual-source scans at pitch=3.2 for spatial and low contrast resolution, CT number accuracy and linearity, SSPs, image uniformity, and noise. The pitch value (1.6{<=}pitch{<=}3.2) had only a minor impact on radiation dose and image noise when the effective tube current time product (mA s/pitch) was kept constant. However, while not severe, artifacts were found to be more prevalent for the dual-source pitch=3.2 scan mode when structures varied markedly along the z axis, particularly for head scans. Images of the moving

  5. Performance evaluation of a 64-slice CT system with z-flying focal spot.

    PubMed

    Flohr, T; Stierstorfer, K; Raupach, R; Ulzheimer, S; Bruder, H

    2004-12-01

    The meanwhile established generation of 16-slice CT systems enables routine sub-millimeter imaging at short breath-hold times. Clinical progress in the development of multidetector row CT (MDCT) technology beyond 16 slices can more likely be expected from further improvement in spatial and temporal resolution rather than from a mere increase in the speed of volume coverage. We present an evaluation of a recently introduced 64-slice CT system (SOMATOM Sensation 64, Siemens AG, Forchheim, Germany), which uses a periodic motion of the focal spot in longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. This technique acquires 64 overlapping 0.6 mm slices per rotation. The sampling scheme corresponds to that of a 64 x 0.3 mm detector, with the goal of improved longitudinal resolution and reduced spiral artifacts. After an introduction to the detector design, we discuss the basics of z-flying focal spot technology (z-Sharp). We present phantom and specimen scans for performance evaluation. The measured full width at half maximum (FWHM) of the thinnest spiral slice is 0.65 mm. All spiral slice widths are almost independent of the pitch, with deviations of less than 0.1 mm from the nominal value. Using a high-resolution bar pattern phantom (CATPHAN, Phantom Laboratories, Salem, NY), the longitudinal resolution can be demonstrated to be up to 15 lp/cm at the isocenter independent of the pitch, corresponding to a bar diameter of 0.33 mm. Longitudinal resolution is only slightly degraded for off-center locations. At a distance of 100 mm from the isocenter, 14 lp/cm can be resolved in the z-direction, corresponding to a bar diameter of 0.36 mm. Spiral "windmill" artifacts presenting as hyper- and hypodense structures around osseous edges are effectively reduced by the z-flying focal spot technique. Cardiac scanning benefits from the short gantry rotation time of 0.33 s, providing up to 83 ms temporal resolution with 2-segment ECG

  6. A Monte Carlo-based method to estimate radiation dose from spiral CT: from phantom testing to patient-specific models

    NASA Astrophysics Data System (ADS)

    Jarry, G.; DeMarco, J. J.; Beifuss, U.; Cagnon, C. H.; McNitt-Gray, M. F.

    2003-08-01

    The purpose of this work is to develop and test a method to estimate the relative and absolute absorbed radiation dose from axial and spiral CT scans using a Monte Carlo approach. Initial testing was done in phantoms and preliminary results were obtained from a standard mathematical anthropomorphic model (MIRD V) and voxelized patient data. To accomplish this we have modified a general purpose Monte Carlo transport code (MCNP4B) to simulate the CT x-ray source and movement, and then to calculate absorbed radiation dose in desired objects. The movement of the source in either axial or spiral modes was modelled explicitly while the CT system components were modelled using published information about x-ray spectra as well as information provided by the manufacturer. Simulations were performed for single axial scans using the head and body computed tomography dose index (CTDI) polymethylmethacrylate phantoms at both central and peripheral positions for all available beam energies and slice thicknesses. For comparison, corresponding physical measurements of CTDI in phantom were made with an ion chamber. To obtain absolute dose values, simulations and measurements were performed in air at the scanner isocentre for each beam energy. To extend the verification, the CT scanner model was applied to the MIRD V model and compared with published results using similar technical factors. After verification of the model, the generalized source was simulated and applied to voxelized models of patient anatomy. The simulated and measured absolute dose data in phantom agreed to within 2% for the head phantom and within 4% for the body phantom at 120 and 140 kVp; this extends to 8% for the head and 9% for the body phantom across all available beam energies and positions. For the head phantom, the simulated and measured absolute dose data agree to within 2% across all slice thicknesses at 120 kVp. Our results in the MIRD phantom agree within 11% of all the different organ dose values

  7. Evaluation of Distal Femoral Rotational Alignment with Spiral CT Scan before Total Knee Arthroplasty (A Study in Iranian population)

    PubMed Central

    Jabalameli, Mahmoud; Moradi, Amin; Bagherifard, Abolfazl; Radi, Mehran; Mokhtari, Tahmineh

    2016-01-01

    Background: Evaluating the landmarks for rotation of the distal femur is a challenge for orthopedic surgeons. Although the posterior femoral condyle axis is a good landmark for surgeons, the surgical transepicondylar axis may be a better option with the help of preoperative CT scanning. The purpose of this study was to ascertain relationships among the axes’ guiding distal femur rotational alignment in preoperative CT scans of Iranian patients who were candidates for total knee arthroplasty and the effects of age, gender, and knee alignment on these relationships. Methods: One hundred and eight cases who were admitted to two university hospitals for total knee arthroplasty were included in this study. The rotation of the distal femur was evaluated using single axial CT images through the femoral epicondyle. Four lines were drawn digitally in this view: anatomical and surgical transepicondylar axes, posterior condylar axis and the Whiteside anteroposterior line. The alignment of the extremity was evaluated in the standing alignment view. Then the angles were measured along these lines and their relationship was evaluated. Results: The mean angle between the anatomical transepicondylar axis and posterior condylar axis and between the surgical transepicondylar axis and posterior condylar axis were 5.9 ± 1.6 degrees and 1.6±1.7 degrees respectively. The mean angle between the Whiteside’s anteroposterior line and the line perpendicular to the posterior condylar axis was 3.7±2.1 degrees. Significant differences existed between the two genders in these relationships. No significant correlation between the age of patients and angles of the distal femur was detected. The anatomical surgical transepicondylar axis was in 4.3 degrees external rotation in relation to the surgical transepicondylar axis. Conclusion: Preoperative CT scanning can help accurately determine rotational landmarks of the distal femur. If one of the reference axes cannot be determined, other

  8. CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. Modern spiral scanners can perform the exam without stopping. A computer ...

  9. Spirality: Spiral arm pitch angle measurement

    NASA Astrophysics Data System (ADS)

    Shields, Douglas W.; Boe, Benjamin; Pfountz, Casey; Davis, Benjamin L.; Hartley, Matthew; Pour Imani, Hamed; Slade, Zac; Kennefick, Daniel; Kennefick, Julia

    2015-12-01

    Spirality measures spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Written in MATLAB, the code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined.

  10. Frequency spirals

    NASA Astrophysics Data System (ADS)

    Ottino-Löffler, Bertrand; Strogatz, Steven H.

    2016-09-01

    We study the dynamics of coupled phase oscillators on a two-dimensional Kuramoto lattice with periodic boundary conditions. For coupling strengths just below the transition to global phase-locking, we find localized spatiotemporal patterns that we call "frequency spirals." These patterns cannot be seen under time averaging; they become visible only when we examine the spatial variation of the oscillators' instantaneous frequencies, where they manifest themselves as two-armed rotating spirals. In the more familiar phase representation, they appear as wobbly periodic patterns surrounding a phase vortex. Unlike the stationary phase vortices seen in magnetic spin systems, or the rotating spiral waves seen in reaction-diffusion systems, frequency spirals librate: the phases of the oscillators surrounding the central vortex move forward and then backward, executing a periodic motion with zero winding number. We construct the simplest frequency spiral and characterize its properties using analytical and numerical methods. Simulations show that frequency spirals in large lattices behave much like this simple prototype.

  11. High-pitch spiral CT with 3D reformation: an alternative choice for imaging vascular anomalies with affluent blood flow in the head and neck of infants and children

    PubMed Central

    Li, H-O; Huo, R; Xu, G-Q; Duan, Y-H; Nie, P; Ji, X-P; Cheng, Z-P; Xu, Z-D

    2015-01-01

    Objective: To evaluate the feasibility of high-pitch spiral CT in imaging vascular anomalies (VAs) with affluent blood flow in the head and neck of infants and children. Methods: For patients with suspected VAs and affluent blood flow pre-detected by ultrasound, CT was performed with high-pitch mode, individualized low-dose scan protocol and three-dimensional (3D) reformation. A five-point scale was used for image quality evaluation. Diagnostic accuracy was calculated with clinical diagnosis with/without pathological results as the reference standard. Radiation exposure and single-phase scan time were recorded. Treatment strategies were formulated based on CT images and results and were monitored through follow-up results. Results: 20 lesions were identified in 15 patients (median age of 11 months). The mean score of image quality was 4.13 ± 0.74. 7 patients (7/15, 46.67%) were diagnosed with haemangiomas, 6 patients (6/15, 40%) were diagnosed with venous malformations and 2 patients (2/15, 13.33%) were diagnosed with arteriovenous malformations. The average effective radiation doses of a single phase and of the total procedure were 0.27 ± 0.08 and 0.86 ± 0.21 mSv. The average scanning time of a single phase was 0.46 ± 0.09 s. After treatment, 13 patients (13/15, 86.67%) achieved excellent results, and 2 patients (2/15, 13.33%) showed good results in follow-up visits. Conclusion: High-pitch spiral CT with an individualized low-dose scan protocol and 3D reformation is an effective modality for imaging VAs with affluent blood flow in the head and neck of infants and children when vascular details are needed and ultrasound and MRI could not provide the complete information. Advances in knowledge: This study proposes an alternative modality for imaging VAs with affluent blood flow. PMID:26055504

  12. [Application of computed tomography (CT) examination for forensic medicine].

    PubMed

    Urbanik, Andrzej; Chrzan, Robert

    2013-01-01

    The aim of the study is to present a own experiences in usage of post mortem CT examination for forensic medicine. With the help of 16-slice CT scanner 181 corpses were examined. Obtained during acquisition imaging data are later developed with dedicated programmes. Analyzed images were extracted from axial sections, multiplanar reconstructions as well as 3D reconstructions. Gained information helped greatly when classical autopsy was performed by making it more accurate. A CT scan images recorded digitally enable to evaluate corpses at any time, despite processes of putrefaction or cremation. If possible CT examination should precede classical autopsy. PMID:23944089

  13. Thoracic spine CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam without stopping.) A computer ...

  14. Spiral tectonics

    NASA Astrophysics Data System (ADS)

    Hassan Asadiyan, Mohammad

    2014-05-01

    Spiral Tectonics (ST) is a new window to global tectonics introduced as alternative model for Plate Tectonics (PT). ST based upon Dahw(rolling) and Tahw(spreading) dynamics. Analogues to electric and magnetic components in the electromagnetic theory we could consider Dahw and Tahw as components of geodynamics, when one component increases the other decreases and vice versa. They are changed to each other during geological history. D-component represents continental crust and T-component represents oceanic crust. D and T are two arm of spiral-cell. T-arm 180 degree lags behind D-arm so named Retard-arm with respect to D or Forward-arm. It seems primary cell injected several billions years ago from Earth's center therefore the Earth's core was built up first then mantel and finally the crust was build up. Crust building initiate from Arabia (Mecca). As the universe extended gravitation wave swirled the earth fractaly along cycloid path from big to small scale. In global scale (order-0) ST collect continents in one side and abandoned Pacific Ocean in the other side. Recent researches also show two mantels upwelling in opposite side of the Earth: one under Africa (tectonic pose) and the other under Pacific Ocean (tectonic tail). In higher order (order-1) ST build up Africa in one side and S.America in the other side therefore left Atlantic Ocean meandered in between. In order-n e.g. Khoor Musa and Bandar-Deylam bay are seen meandered easterly in the Iranian part but Khoor Abdullah and Kuwait bay meandered westerly in the Arabian part, they are distributed symmetrically with respect to axis of Persian Gulf(PG), these two are fractal components of easterly Caspian-wing and westerly Black Sea-wing which split up from Anatoly. Caspian Sea and Black Sea make two legs of Y-like structure, this shape completely fitted with GPS-velocity map which start from PG and split up in the Catastrophic Point(Anatoly). We could consider PG as remnants of Ancient Ocean which spent up

  15. Quantum spirals

    NASA Astrophysics Data System (ADS)

    Yoshida, Z.; Mahajan, S. M.

    2016-02-01

    Quantum systems often exhibit fundamental incapability to entertain vortex. The Meissner effect, a complete expulsion of the magnetic field (the electromagnetic vorticity), for instance, is taken to be the defining attribute of the superconducting state. Superfluidity is another, close-parallel example; fluid vorticity can reside only on topological defects with a limited (quantized) amount. Recent developments in the Bose-Einstein condensates produced by particle traps further emphasize this characteristic. We show that the challenge of imparting vorticity to a quantum fluid can be met through a nonlinear mechanism operating in a hot fluid corresponding to a thermally modified Pauli-Schrödinger spinor field. The thermal baroclinic effect is represented by a nonlinear, non-Hermitian Hamiltonian, which, in conjunction with spin vorticity, leads to new interesting quantum states; a spiral solution is explicitly worked out in a simple field-free model.

  16. Rational diagnosis of pulmonary embolism (RADIA PE) in symptomatic outpatients with suspected PE: an improved strategy to exclude or diagnose venous thromboembolism by the sequential use of a clinical model, rapid ELISA D-dimer test, perfusion lung scan, ultrasonography, spiral CT, and pulmonary angiography.

    PubMed

    Michiels, J J

    1998-01-01

    A prospective management decision analysis for the exclusion and diagnosis of pulmonary embolism (PE) based on pre-test clinical probability (PCP) estimation for PE, a rapid ELISA D-dimer test, perfusion lungscan (P-scan), CUS, spiral CT, and pulmonary angiography is proposed. The modified PCP model for PE of Wells et al. allows reasonably accurate classification of patients with no, low, moderate, and high probability for PE. The combined rational use of the evidence-based noninvasive imaging techniques P-scan, CUS, and spiral CT with the rapid ELISA D-dimer test and PCP will reduce the need for invasive pulmonary angiography to perhaps 10 to 15% of patients, who initially presented with suspected PE. A Rational Diagnosis of Pulmonary Embolism (RADIA PE) model is proposed for testing in a large multicenter study of patients with suspected PE. PMID:9763360

  17. Radiation Exposure of Ovarian Cancer Patients: Contribution of CT Examinations Performed on Different MDCT (16 and 64 Slices) Scanners and Image Quality Evaluation

    PubMed Central

    Rizzo, Stefania; Origgi, Daniela; Brambilla, Sarah; De Maria, Federica; Foà, Riccardo; Raimondi, Sara; Colombo, Nicoletta; Bellomi, Massimo

    2015-01-01

    Abstract The objective of this study is to compare radiation doses given to ovarian cancer patients by different computed tomographies (CTs) and to evaluate association between doses and subjective and objective image quality. CT examinations included were performed either on a 16-slice CT, equipped with automatic z-axis tube current modulation, or on a 64-slice CT, equipped with z-axis, xy-axis modulation, and adaptive statistical iterative algorithm (ASIR). Evaluation of dose included the following dose descriptors: volumetric CT dose index (CTDIvol), dose length product (DLP), and effective dose (E). Objective image noise was evaluated in abdominal aorta and liver. Subjective image quality was evaluated by assessment of image noise, spatial resolution and diagnostic acceptability. Mean and median CTDIvol, DLP, and E; correlation between CTDIvol and DLP and patients’ weight; comparison of objective noise for the 2 scanners; association between dose descriptors and subjective image quality. The 64-slice CT delivered to patients 24.5% lower dose (P < 0.0001) than 16-slice CT. There was a significant correlation between all dose descriptors (CTDIvol, DLP, E) and weight (P < 0.0001). Objective noise was comparable for the 2 CT scanners. There was a significant correlation between dose descriptors and image noise for the 64-slice CT, and between dose descriptors and spatial resolution for the 16-slice CT. Current dose reduction systems may reduce radiation dose without significantly affecting image quality and diagnostic acceptability of CT exams. PMID:25929914

  18. Radiation exposure of ovarian cancer patients: contribution of CT examinations performed on different MDCT (16 and 64 slices) scanners and image quality evaluation: an observational study.

    PubMed

    Rizzo, Stefania; Origgi, Daniela; Brambilla, Sarah; De Maria, Federica; Foà, Riccardo; Raimondi, Sara; Colombo, Nicoletta; Bellomi, Massimo

    2015-05-01

    The objective of this study is to compare radiation doses given to ovarian cancer patients by different computed tomographies (CTs) and to evaluate association between doses and subjective and objective image quality.CT examinations included were performed either on a 16-slice CT, equipped with automatic z-axis tube current modulation, or on a 64-slice CT, equipped with z-axis, xy-axis modulation, and adaptive statistical iterative algorithm (ASIR). Evaluation of dose included the following dose descriptors: volumetric CT dose index (CTDIvol), dose length product (DLP), and effective dose (E). Objective image noise was evaluated in abdominal aorta and liver. Subjective image quality was evaluated by assessment of image noise, spatial resolution and diagnostic acceptability.Mean and median CTDIvol, DLP, and E; correlation between CTDIvol and DLP and patients' weight; comparison of objective noise for the 2 scanners; association between dose descriptors and subjective image quality.The 64-slice CT delivered to patients 24.5% lower dose (P < 0.0001) than 16-slice CT. There was a significant correlation between all dose descriptors (CTDIvol, DLP, E) and weight (P < 0.0001). Objective noise was comparable for the 2 CT scanners. There was a significant correlation between dose descriptors and image noise for the 64-slice CT, and between dose descriptors and spatial resolution for the 16-slice CT.Current dose reduction systems may reduce radiation dose without significantly affecting image quality and diagnostic acceptability of CT exams. PMID:25929914

  19. PET/CT: fundamental principles.

    PubMed

    Seemann, Marcus D

    2004-05-28

    Positron emission tomography (PET) facilitates the evaluation of metabolic and molecular characteristics of a wide variety of cancers, but is limited in its ability to visualize anatomical structures. Computed tomography (CT) facilitates the evaluation of anatomical structures of cancers, but can not visualize their metabolic and molecular aspects. Therefore, the combination of PET and CT provides the ability to accurately register metabolic and molecular aspects of disease with anatomical findings, adding further information to the diagnosis and staging of tumors. The recent generation of high performance PET/CT scanners combines a state of the art full-ring 3D PET scanner and a high-end 16-slice CT scanner. In PET/CT scanners, a CT examination is used for attenuation correction of PET images rather than standard transmission scanning using superset 68 Ge sources. This reduces the examination time, but metallic objects and contrast agents that alter the CT image quality and quantitative measurements of standardized uptake values (SUV) may lead to artifacts in the PET images. Hybrid PET/CT imaging will be very important in oncological applications in the decades to come, and possibly for use in cancer screening and cardiac imaging. PMID:15257877

  20. Method for transforming CT images for attenuation correction in PET/CT imaging

    SciTech Connect

    Carney, Jonathan P.J.; Townsend, David W.; Rappoport, Vitaliy; Bendriem, Bernard

    2006-04-15

    A tube-voltage-dependent scheme is presented for transforming Hounsfield units (HU) measured by different computed tomography (CT) scanners at different x-ray tube voltages (kVp) to 511 keV linear attenuation values for attenuation correction in positron emission tomography (PET) data reconstruction. A Gammex 467 electron density CT phantom was imaged using a Siemens Sensation 16-slice CT, a Siemens Emotion 6-slice CT, a GE Lightspeed 16-slice CT, a Hitachi CXR 4-slice CT, and a Toshiba Aquilion 16-slice CT at kVp ranging from 80 to 140 kVp. All of these CT scanners are also available in combination with a PET scanner as a PET/CT tomograph. HU obtained for various reference tissue substitutes in the phantom were compared with the known linear attenuation values at 511 keV. The transformation, appropriate for lung, soft tissue, and bone, yields the function 9.6x10{sup -5}{center_dot}(HU+1000) below a threshold of {approx}50 HU and a{center_dot}(HU+1000)+b above the threshold, where a and b are fixed parameters that depend on the kVp setting. The use of the kVp-dependent scaling procedure leads to a significant improvement in reconstructed PET activity levels in phantom measurements, resolving errors of almost 40% otherwise seen for the case of dense bone phantoms at 80 kVp. Results are also presented for patient studies involving multiple CT scans at different kVp settings, which should all lead to the same 511 keV linear attenuation values. A linear fit to values obtained from 140 kVp CT images using the kVp-dependent scaling plotted as a function of the corresponding values obtained from 80 kVp CT images yielded y=1.003x-0.001 with an R{sup 2} value of 0.999, indicating that the same values are obtained to a high degree of accuracy.

  1. [Clinical role of spiral tomodensitometry in pulmonary disorders].

    PubMed

    Scillia, P; Sy, M; Chaminade, L; Gevenois, P A

    1995-04-01

    Spiral CT of the lungs has taken the place of conventional CT in most indications. Until now, some specific indications, concerning the detection of lung nodules, the detection of central pulmonary thromboembolism and the description of the angioarchitecture of pulmonary arteriovenous malformations have been reported. This paper provides an overview of the clinical utility of this new technique. PMID:7601819

  2. Multiarmed Spirals in Excitable Media

    NASA Astrophysics Data System (ADS)

    Vasiev, Bakthier; Siegert, Florian; Weijer, Cornelis

    1997-03-01

    Numerical studies of the properties of multiarmed spirals show that they can form spontaneously in low excitability media. The maximum number of arms in a multiarmed spiral is proportional to the ratio of the single spiral period to the refractoriness of the medium. Multiarmed spirals are formed due to attraction of single spirals if these spirals rotate in the same direction and their tips are less than one wavelength apart, i.e., a spiral broken not far from its tip can evolve into a 2-armed spiral. We propose this mechanism to be responsible for the formation of multiarmed spirals in mounds of the slime mold Dictyostelium discoideum.

  3. Electromechanics of graphene spirals

    SciTech Connect

    Korhonen, Topi; Koskinen, Pekka

    2014-12-15

    Among the most fascinating nanostructure morphologies are spirals, hybrids of somewhat obscure topology and dimensionality with technologically attractive properties. Here, we investigate mechanical and electromechanical properties of graphene spirals upon elongation by using density-functional tight-binding, continuum elasticity theory, and classical force field molecular dynamics. It turns out that electronic properties are governed by interlayer interactions as opposed to strain effects. The structural behavior is governed by van der Waals interaction: in its absence spirals unfold with equidistant layer spacings, ripple formation at spiral perimeter, and steadily increasing axial force; in its presence, on the contrary, spirals unfold via smooth local peeling, complex geometries, and nearly constant axial force. These electromechanical trends ought to provide useful guidelines not only for additional theoretical investigations but also for forthcoming experiments on graphene spirals.

  4. Spiral Flow Separator

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A.

    1993-01-01

    Proposed liquid-separating device relies on centrifugal force in liquid/liquid or liquid/solid mixture in spiral path. Operates in continuous flow at relatively high rates. Spiral tubes joined in sequence, with outlet tubes connected to joints. Cross-sectional areas of successive spiral tubes decreases by cross-sectional areas of outlet tubes. Centrifugal force pushes denser particles or liquids to outer edge of spiral, where removed from flow. Principle exploited to separate solids from wastewater, oil from fresh or salt water, or contaminants from salt water before evaporation. Also used to extract such valuable materials as precious metals from slurries.

  5. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi

    The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.

  6. Spiral model of pitch

    NASA Astrophysics Data System (ADS)

    Miller, James D.

    2003-10-01

    A spiral model of pitch interrelates tone chroma, tone height, equal temperament scales, and a cochlear map. Donkin suggested in 1870 that the pitch of tones could be well represented by an equiangular spiral. More recently, the cylindrical helix has been popular for representing tone chroma and tone height. Here it is shown that tone chroma, tone height, and cochlear position can be conveniently related to tone frequency via a planar spiral. For this ``equal-temperament spiral,'' (ET Spiral) tone chroma is conceived as a circular array with semitones at 30° intervals. The frequency of sound on the cent scale (re 16.351 Hz) is represented by the radius of the spiral defined by r=(1200/2π)θr, where θr is in radians. By these definitions, one revolution represents one octave, 1200 cents, 30° represents a semitone, the radius relates θ to cents in accordance with equal temperament (ET) tuning, and the arclength of the spiral matches the mapping of sound frequency to the basilar membrane. Thus, the ET Spiral gives tone chroma as θ, tone height as the cent scale, and the cochlear map as the arclength. The possible implications and directions for further work are discussed.

  7. Superluminous Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ogle, Patrick M.; Lanz, Lauranne; Nader, Cyril; Helou, George

    2016-02-01

    We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity Lr = 8-14L* (4.3-7.5 × 1044 erg s-1). These super spiral galaxies are also giant and massive, with diameter D = 57-134 kpc and stellar mass Mstars = 0.3-3.4 × 1011M⊙. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z < 0.3 and Lr > 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M⊙ yr-1 place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.

  8. Spiral fluid separator

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A. (Inventor)

    1993-01-01

    A fluid separator for separating particulate matter such as contaminates is provided which includes a series of spiral tubes of progressively decreasing cross sectional area connected in series. Each tube has an outlet on the outer curvature of the spiral. As fluid spirals down a tube, centrifugal force acts to force the heavier particulate matter to the outer wall of the tube, where it exits through the outlet. The remaining, and now cleaner, fluid reaches the next tube, which is smaller in cross sectional area, where the process is repeated. The fluid which comes out the final tube is diminished of particulate matter.

  9. Spiral concentrators recover fine coal

    SciTech Connect

    Fiscor, S.

    2005-12-15

    Compound spirals offer better performance in a more efficient configuration. Prep plant operators in the US are increasingly opting to use spiral concentrators. They are easy to install, operate and maintain but their downfall is low capacity. The article describes spirals available from PrepTech/Multotec, Krebs Engineers and Roche MT. It reports on research on spiral concentrator technology. 1 ref., 4 figs.

  10. Assessment of multislice CT to quantify pulmonary emphysema function and physiology in a rat model

    NASA Astrophysics Data System (ADS)

    Cao, Minsong; Stantz, Keith M.; Liang, Yun; Krishnamurthi, Ganapathy; Presson, Robert G., Jr.

    2005-04-01

    Purpose: The purpose of this study is to evaluate multi-slice computed tomography technology to quantify functional and physiologic changes in rats with pulmonary emphysema. Method: Seven rats were scanned using a 16-slice CT (Philips MX8000 IDT) before and after artificial inducement of emphysema. Functional parameters i.e. lung volumes were measured by non-contrast spiral scan during forced breath-hold at inspiration and expiration followed by image segmentation based on attenuation threshold. Dynamic CT imaging was performed immediately following the contrast injection to estimate physiology changes. Pulmonary perfusion, fractional blood volume, and mean transit times (MTTs) were estimated by fitting the time-density curves of contrast material using a compartmental model. Results: The preliminary results indicated that the lung volumes of emphysema rats increased by 3.52+/-1.70mL (p<0.002) at expiration and 4.77+/-3.34mL (p<0.03) at inspiration. The mean lung densities of emphysema rats decreased by 91.76+/-68.11HU (p<0.01) at expiration and low attenuation areas increased by 5.21+/-3.88% (p<0.04) at inspiration compared with normal rats. The perfusion for normal and emphysema rats were 0.25+/-0.04ml/s/ml and 0.32+/-0.09ml/s/ml respectively. The fractional blood volumes for normal and emphysema rats were 0.21+/-0.04 and 0.15+/-0.02. There was a trend toward faster MTTs for emphysema rats (0.42+/-0.08s) than normal rats (0.89+/-0.19s) with p<0.006, suggesting that blood flow crossing the capillaries increases as the capillary volume decreases and which may cause the red blood cells to leave the capillaries incompletely saturated with oxygen if the MTTs become too short. Conclusion: Quantitative measurement using CT of structural and functional changes in pulmonary emphysema appears promising for small animals.

  11. High assurance SPIRAL

    NASA Astrophysics Data System (ADS)

    Franchetti, Franz; Sandryhaila, Aliaksei; Johnson, Jeremy R.

    2014-06-01

    In this paper we introduce High Assurance SPIRAL to solve the last mile problem for the synthesis of high assurance implementations of controllers for vehicular systems that are executed in today's and future embedded and high performance embedded system processors. High Assurance SPIRAL is a scalable methodology to translate a high level specification of a high assurance controller into a highly resource-efficient, platform-adapted, verified control software implementation for a given platform in a language like C or C++. High Assurance SPIRAL proves that the implementation is equivalent to the specification written in the control engineer's domain language. Our approach scales to problems involving floating-point calculations and provides highly optimized synthesized code. It is possible to estimate the available headroom to enable assurance/performance trade-offs under real-time constraints, and enables the synthesis of multiple implementation variants to make attacks harder. At the core of High Assurance SPIRAL is the Hybrid Control Operator Language (HCOL) that leverages advanced mathematical constructs expressing the controller specification to provide high quality translation capabilities. Combined with a verified/certified compiler, High Assurance SPIRAL provides a comprehensive complete solution to the efficient synthesis of verifiable high assurance controllers. We demonstrate High Assurance SPIRALs capability by co-synthesizing proofs and implementations for attack detection and sensor spoofing algorithms and deploy the code as ROS nodes on the Landshark unmanned ground vehicle and on a Synthetic Car in a real-time simulator.

  12. Voronoi spiral tilings

    NASA Astrophysics Data System (ADS)

    Yamagishi, Yoshikazu; Sushida, Takamichi; Hizume, Akio

    2015-04-01

    The parameter set of Voronoi spiral tilings gives a dual of van Iterson's bifurcation diagram for phyllotactic spirals. We study the Voronoi tilings for the Bernoulli spiral site sets, as the simplest spirals in the centric representation with similarity symmetry. Their parameter set is composed of a family of real algebraic curves in the complex plane, with the Farey sequence structure. This naturally extends to the parameter set for multiple tilings, i.e., the tilings of the covering spaces of the punctured plane. We show the denseness of the parameters z = reiθ for quadrilateral Voronoi spiral multiple tilings. The techniques of dynamical systems are applied to the group of similarity symmetry. The parastichy numbers and the distortion of the Voronoi regions depend on the rational approximations of θ/2π. We consider the limit set of the shapes of the quadrilateral tiles by taking the limit as r → 1, with θ fixed. If θ/2π is a quadratic irrational number, then the limit set is a finite set of rectangles. In particular, if θ/2π is linearly equivalent to the golden section, then the limit is the square.

  13. Spiral MR myocardial tagging.

    PubMed

    Ryf, Salome; Kissinger, Kraig V; Spiegel, Marcus A; Börnert, Peter; Manning, Warren J; Boesiger, Peter; Stuber, Matthias

    2004-02-01

    In the present study, complementary spatial modulation of magnetization (CSPAMM) myocardial tagging was extended with an interleaved spiral imaging sequence. The use of a spiral sequence enables the acquisition of grid-tagged images with a tagline distance as low as 4 mm in a single breath-hold. Alternatively, a high temporal resolution of 77 frames per second was obtained with 8-mm grid spacing. Ten healthy adult subjects were studied. With this new approach, high-quality images can be obtained and the tags persist throughout the entire cardiac cycle. PMID:14755646

  14. Imaging study on the optic canal using sixty four-slice spiral computed tomography

    PubMed Central

    Jiang, Peng-Fei; Dai, Xiu-Yu; Lv, Yongbin; Liu, Shaoyi; Mu, Xiao-Yan

    2015-01-01

    Background: Rapid advances in multislice computed tomography (MSCT) technology facilitate accurate clinical imaging. The newly developed 64-slice CT increases temporal and spatial resolution efficiently. Purpose: The purpose of this study is to evaluate the application of 64 slice spiral computed tomography (CT) on the imaging of the normal optics canal. Methods and materials: 100 healthy adults were investigated using 64 slice spiral CT. The optics canal was scanned, reconstructed and examined. Results: Among the four walls of the optic canal, the medial wall is the longest one. The upper wall and outer wall are inferior to the medial wall while the inferior wall is the shortest one. All the data accomplished by the 64 slice CT was consistent with the results of previous reports using other methods. Conclusion: The results suggested that the 64 slice spiral CT could be a valuable and accurate method for measuring the length of optics canal walls. PMID:26885062

  15. Dose management in CT facility

    PubMed Central

    Tsapaki, V; Rehani, M

    2007-01-01

    Computed Tomography (CT) examinations have rapidly increased in number over the last few years due to recent advances such as the spiral, multidetector-row, CT fluoroscopy and Positron Emission Tomography (PET)-CT technology. This has resulted in a large increase in collective radiation dose as reported by many international organisations. It is also stated that frequently, image quality in CT exceeds the level required for confident diagnosis. This inevitably results in patient radiation doses that are higher than actually required, as also stressed by the US Food and Drug Administration (FDA) regarding the CT exposure of paediatric and small adult patients. However, the wide range in exposure parameters reported, as well as the different CT applications reveal the difficulty in standardising CT procedures. The purpose of this paper is to review the basic CT principles, outline the recent technological advances and their impact in patient radiation dose and finally suggest methods of radiation dose optimisation. PMID:21614279

  16. Spiral Waves in Accretion Disks

    NASA Astrophysics Data System (ADS)

    Harlaftis, Emilios

    A review with the most characteristic spiral waves in accretion disks of cataclysmic variables will be presented. Recent work on experiments targeting the detection of spiral waves from time lapse movies of real disks and the study of permanent spiral waves will be discussed. The relevance of spiral waves with other systems such as star-planet X-ray binaries and Algols will be reviewed.

  17. Are spiral galaxies heavy smokers

    SciTech Connect

    Davies, J.; Disney, M.; Phillipps, S )

    1990-07-01

    The dustiness of spiral galaxies is discussed. Starburst galaxies and the shortage of truly bright spiral galaxies is cited as evidence that spiral galaxies are far dustier than has been thought. The possibility is considered that the dust may be hiding missing mass.

  18. Ubibliotheca The Spiral Library.

    ERIC Educational Resources Information Center

    Ottewell, Guy

    A plan for a library with a storage level in the shape of a flat spiral is presented. The advantages of such a plan include: space saving, easy expansion of the building, an unbroken sequence of shelving, quick access to all books and freedom in the design of the library's other sectors. This plan is especially suited for the research library…

  19. Spiral track oven

    SciTech Connect

    Drobilisch, Sandor

    1998-12-20

    Final report on development of a continuously operating oven system in which the parts are progressing automatically on a spiral track for in-line service installation for the production of electronic and/or other components to be heat cured or dried.

  20. Spiral wound extraction cartridge

    DOEpatents

    Wisted, Eric E.; Lundquist, Susan H.

    1999-01-01

    A cartridge device for removing an analyte from a fluid comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and optionally at least one reinforcing spacer sheet, the particulate being capable of binding the analyte, the sheet composite being formed into a spiral configuration about the core, wherein the sheet composite is wound around itself and wherein the windings of sheet composite are of sufficient tightness so that adjacent layers are essentially free of spaces therebetween, two end caps which are disposed over the core and the lateral ends of the spirally wound sheet composite, and means for securing the end caps to the core, the end caps also being secured to the lateral ends of the spirally wound sheet composite. A method for removing an analyte from a fluid comprises the steps of providing a spirally wound element of the invention and passing the fluid containing the analyte through the element essentially normal to a surface of the sheet composite so as to bind the analyte to the particulate of the particulate-loaded porous membrane, the method optionally including the step of eluting the bound analyte from the sheet composite.

  1. Spiral Galaxies Stripped Bare

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Six spectacular spiral galaxies are seen in a clear new light in images from ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile. The pictures were taken in infrared light, using the impressive power of the HAWK-I camera, and will help astronomers understand how the remarkable spiral patterns in galaxies form and evolve. HAWK-I [1] is one of the newest and most powerful cameras on ESO's Very Large Telescope (VLT). It is sensitive to infrared light, which means that much of the obscuring dust in the galaxies' spiral arms becomes transparent to its detectors. Compared to the earlier, and still much-used, VLT infrared camera ISAAC, HAWK-I has sixteen times as many pixels to cover a much larger area of sky in one shot and, by using newer technology than ISAAC, it has a greater sensitivity to faint infrared radiation [2]. Because HAWK-I can study galaxies stripped bare of the confusing effects of dust and glowing gas it is ideal for studying the vast numbers of stars that make up spiral arms. The six galaxies are part of a study of spiral structure led by Preben Grosbøl at ESO. These data were acquired to help understand the complex and subtle ways in which the stars in these systems form into such perfect spiral patterns. The first image shows NGC 5247, a spiral galaxy dominated by two huge arms, located 60-70 million light-years away. The galaxy lies face-on towards Earth, thus providing an excellent view of its pinwheel structure. It lies in the zodiacal constellation of Virgo (the Maiden). The galaxy in the second image is Messier 100, also known as NGC 4321, which was discovered in the 18th century. It is a fine example of a "grand design" spiral galaxy - a class of galaxies with very prominent and well-defined spiral arms. About 55 million light-years from Earth, Messier 100 is part of the Virgo Cluster of galaxies and lies in the constellation of Coma Berenices (Berenice's Hair, named after the ancient Egyptian queen Berenice II). The third

  2. Spiral wound extraction cartridge

    DOEpatents

    Wisted, E.E.; Lundquist, S.H.

    1999-04-27

    A cartridge device for removing an analyte from a fluid comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and optionally at least one reinforcing spacer sheet, the particulate being capable of binding the analyte, the sheet composite being formed into a spiral configuration about the core, wherein the sheet composite is wound around itself and wherein the windings of sheet composite are of sufficient tightness so that adjacent layers are essentially free of spaces therebetween, two end caps which are disposed over the core and the lateral ends of the spirally wound sheet composite, and means for securing the end caps to the core, the end caps also being secured to the lateral ends of the spirally wound sheet composite. A method for removing an analyte from a fluid comprises the steps of providing a spirally wound element of the invention and passing the fluid containing the analyte through the element essentially normal to a surface of the sheet composite so as to bind the analyte to the particulate of the particulate-loaded porous membrane, the method optionally including the step of eluting the bound analyte from the sheet composite. 4 figs.

  3. Comparison of Conventional Versus Spiral Computed Tomography with Three Dimensional Reconstruction in Chronic Otitis Media with Ossicular Chain Destruction

    PubMed Central

    Naghibi, Saeed; Seifirad, Sirous; Adami Dehkordi, Mahboobeh; Einolghozati, Sasan; Ghaffarian Eidgahi Moghadam, Nafiseh; Akhavan Rezayat, Amir; Seifirad, Soroush

    2016-01-01

    Background: Chronic otitis media (COM) can be treated with tympanoplasty with or without mastoidectomy. In patients who have undergone middle ear surgery, three-dimensional spiral computed tomography (CT) scan plays an important role in optimizing surgical planning. Objectives: This study was performed to compare the findings of three-dimensional reconstructed spiral and conventional CT scan of ossicular chain study in patients with COM. Patients and Methods: Fifty patients enrolled in the study underwent plane and three dimensional CT scan (PHILIPS-MX 8000). Ossicles changes, mastoid cavity, tympanic cavity, and presence of cholesteatoma were evaluated. Results of the two methods were then compared and interpreted by a radiologist, recorded in questionnaires, and analyzed. Logistic regression test and Kappa coefficient of agreement were used for statistical analyses. Results: Sixty two ears with COM were found in physical examination. A significant difference was observed between the findings of the two methods in ossicle erosion (11.3% in conventional CT vs. 37.1% in spiral CT, P = 0.0001), decrease of mastoid air cells (82.3% in conventional CT vs. 93.5% in spiral CT, P = 0.001), and tympanic cavity opacity (12.9% in conventional CT vs. 40.3% in spiral CT, P=0.0001). No significant difference was observed between the findings of the two methods in ossicle destruction (6.5% conventional CT vs. 56.4% in spiral CT, P = 0.125), and presence of cholesteatoma (3.2% in conventional CT vs. 42% in spiral CT, P = 0.172). In this study, spiral CT scan demonstrated ossicle dislocation in 9.6%, decrease of mastoid air cells in 4.8%, and decrease of volume in the tympanic cavity in 1.6%; whereas, none of these findings were reported in the patients' conventional CT scans. Conclusion: Spiral-CT scan is superior to conventional CT in the diagnosis of lesions in COM before operation. It can be used for detailed evaluation of ossicular chain in such patients. PMID:27127583

  4. Spiral waves in Saturn's rings

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.

    1989-01-01

    Spiral density waves and spiral bending waves have been observed at dozens of locations within Saturn's rings. These waves are excited by resonant gravitational perturbations from moons orbiting outside the ring system. Modeling of spiral waves yields the best available estimates for the mass and the thickness of Saturn's ring system. Angular momentum transport due to spiral density waves may cause significant orbital evolution of Saturn's rings and inner moons. Similar angular momentum transfer may occur in other astrophysical systems such as protoplanetary disks, binary star systems with disks and spiral galaxies with satellites.

  5. Forming Spirals From Shadows

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    What causes the large-scale spiral structures found in some protoplanetary disks? Most models assume theyre created by newly-forming planets, but a new study suggests that planets might have nothing to do with it.Perturbations from Planets?In some transition disks protoplanetary disks with gaps in their inner regions weve directly imaged large-scale spiral arms. Many theories currently attribute the formation of these structures to young planets: either the direct perturbations of a planet embedded in the disk cause the spirals, or theyre indirectly caused by the orbit of a planetary body outside of the arms.Another example of spiral arms detected in a protoplanetary disk, MWC 758. [NASA/ESA/ESO/M. Benisty et al.]But what if you could get spirals without any planets? A team of scientists led by Matas Montesinos (University of Chile) have recently published a study in which they examine what happens to a shadowed protoplanetary disk.Casting Shadows with WarpsIn the teams setup, they envision a protoplanetary disk that is warped: the inner region is slightly tilted relative to the outer region. As the central star casts light out over its protoplanetary disk, this disk warping would cause some regions of the disk to be shaded in a way that isnt axially symmetric with potentially interesting implications.Montesinos and collaborators ran 2D hydrodynamics simulations to determine what happens to the motion of particles within the disk when they pass in and out of the shadowed regions. Since the shadowed regions are significantly colder than the illuminated disk, the pressure in these regions is much lower. Particles are therefore accelerated and decelerated as they pass through these regions, and the lack of axial symmetry causes spiral density waves to form in the disk as a result.Initial profile for the stellar heating rate per unit area for one of the authors simulations. The regions shadowed as a result of the disk warp subtend 0.5 radians each (shown on the left

  6. Ferroelectricity in spiral magnets.

    PubMed

    Mostovoy, Maxim

    2006-02-17

    It was recently observed that the ferroelectrics showing the strongest sensitivity to an applied magnetic field are spiral magnets. We present a phenomenological theory of inhomogeneous ferroelectric magnets, which describes their thermodynamics and magnetic field behavior, e.g., dielectric susceptibility anomalies at magnetic transitions and sudden flops of electric polarization in an applied magnetic field. We show that electric polarization can also be induced at domain walls and that magnetic vortices carry electric charge. PMID:16606047

  7. Spiral computed tomography phase-space source model in the BEAMnrc/EGSnrc Monte Carlo system: implementation and validation

    NASA Astrophysics Data System (ADS)

    Kim, Sangroh; Yoshizumi, Terry T.; Yin, Fang-Fang; Chetty, Indrin J.

    2013-04-01

    Currently, the BEAMnrc/EGSnrc Monte Carlo (MC) system does not provide a spiral CT source model for the simulation of spiral CT scanning. We developed and validated a spiral CT phase-space source model in the BEAMnrc/EGSnrc system. The spiral phase-space source model was implemented in the DOSXYZnrc user code of the BEAMnrc/EGSnrc system by analyzing the geometry of spiral CT scan—scan range, initial angle, rotational direction, pitch, slice thickness, etc. Table movement was simulated by changing the coordinates of the isocenter as a function of beam angles. Some parameters such as pitch, slice thickness and translation per rotation were also incorporated into the model to make the new phase-space source model, designed specifically for spiral CT scan simulations. The source model was hard-coded by modifying the ‘ISource = 8: Phase-Space Source Incident from Multiple Directions’ in the srcxyznrc.mortran and dosxyznrc.mortran files in the DOSXYZnrc user code. In order to verify the implementation, spiral CT scans were simulated in a CT dose index phantom using the validated x-ray tube model of a commercial CT simulator for both the original multi-direction source (ISOURCE = 8) and the new phase-space source model in the DOSXYZnrc system. Then the acquired 2D and 3D dose distributions were analyzed with respect to the input parameters for various pitch values. In addition, surface-dose profiles were also measured for a patient CT scan protocol using radiochromic film and were compared with the MC simulations. The new phase-space source model was found to simulate the spiral CT scanning in a single simulation run accurately. It also produced the equivalent dose distribution of the ISOURCE = 8 model for the same CT scan parameters. The MC-simulated surface profiles were well matched to the film measurement overall within 10%. The new spiral CT phase-space source model was implemented in the BEAMnrc/EGSnrc system. This work will be beneficial in estimating the

  8. Galaxy Zoo: passive red spirals

    NASA Astrophysics Data System (ADS)

    Masters, Karen L.; Mosleh, Moein; Romer, A. Kathy; Nichol, Robert C.; Bamford, Steven P.; Schawinski, Kevin; Lintott, Chris J.; Andreescu, Dan; Campbell, Heather C.; Crowcroft, Ben; Doyle, Isabelle; Edmondson, Edward M.; Murray, Phil; Raddick, M. Jordan; Slosar, Anže; Szalay, Alexander S.; Vandenberg, Jan

    2010-06-01

    We study the spectroscopic properties and environments of red (or passive) spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on disc-dominated spirals, we construct a sample of truly passive discs (i.e. they are not dust reddened spirals, nor are they dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spiral galaxies and red early types, making up ~6 per cent of late-type spirals. We use optical images and spectra from Sloan Digital Sky Survey to investigate the physical processes which could have turned these objects red without disturbing their morphology. We find red spirals preferentially in intermediate density regimes. However, there are no obvious correlations between red spiral properties and environment suggesting that environment alone is not sufficient to determine whether a galaxy will become a red spiral. Red spirals are a very small fraction of all spirals at low masses (M* < 1010 Msolar), but are a significant fraction of the spiral population at large stellar masses showing that massive galaxies are red independent of morphology. We confirm that as expected, red spirals have older stellar populations and less recent star formation than the main spiral population. While the presence of spiral arms suggests that a major star formation could not have ceased a long ago (not more than a few Gyr), we show that these are also not recent post-starburst objects (having had no significant star formation in the last Gyr), so star formation must have ceased gradually. Intriguingly, red spirals are roughly four times as likely than the normal spiral population to host optically identified Seyfert/low-ionization nuclear emission region (LINER; at a given stellar mass and even accounting for low-luminosity lines hidden by star formation), with most of the difference coming from the objects with LINER-like emission. We also find a

  9. Stellar Populations in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    MacArthur, L. A.; Courteau, S.; Bell, E. F.; Holtzman, J. A.

    2004-12-01

    We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0--Irr. The colors are compared to stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Relative trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends level off for T ⪉ 4 (Sbc and earlier), V {rot} ⪆ 120 km s-1, MK ⪉ -23 mag, and μ 0 ⪉ 18.5 mag arcsec-2. Outer disk gradients are weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Relative trends in gradients with galaxy parameters do not agree with predictions of semi-analytic models of hierarchical galaxy formation, possibly as a result of bar-induced radial flows. However, the observed trends are in agreement with chemo-spectro photometric models of spiral galaxy evolution based on CDM-motivated scaling laws but including none of the hierarchical merging characteristics. This implies a strong dependence of the star formation history of spiral galaxies on the galaxy potential and halo spin parameter. L.A.M. and S.C acknowledge support

  10. Spiral Microstrip Antenna with Resistance

    NASA Technical Reports Server (NTRS)

    Shively, David G. (Inventor)

    1998-01-01

    A spiral microstrip antenna having resistor elements embedded in each of the spiral arms is provided. The antenna is constructed using a conductive back plane as a base. The back plane supports a dielectric slab having a thickness between one-sixteenth and one-quarter of an inch. A square spiral, having either two or four arms, is attached to the dielectric slab. Each arm of the spiral has resistor elements thereby dissipating an excess energy not already emitted through radiation. The entire configuration provides a thin, flat, high gain, wide bandwidth antenna which requires no underlying cavity. The configuration allows the antenna to be mounted conformably on an aircraft surface.

  11. Spiral Orbit Tribometer

    NASA Technical Reports Server (NTRS)

    Pepper, Stephen V.; Jones, William R., Jr.; Kingsbury, Edward; Jansen, Mark J.

    2007-01-01

    The spiral orbit tribometer (SOT) bridges the gap between full-scale life testing and typically unrealistic accelerated life testing of ball-bearing lubricants in conjunction with bearing ball and race materials. The SOT operates under realistic conditions and quickly produces results, thereby providing information that can guide the selection of lubricant, ball, and race materials early in a design process. The SOT is based upon a simplified, retainerless thrust bearing comprising one ball between flat races (see figure). The SOT measures lubricant consumption and degradation rates and friction coefficients in boundary lubricated rolling and pivoting contacts. The ball is pressed between the lower and upper races with a controlled force and the lower plate is rotated. The combination of load and rotation causes the ball to move in a nearly circular orbit that is, more precisely, an opening spiral. The spiral s pitch is directly related to the friction coefficient. At the end of the orbit, the ball contacts the guide plate, restoring the orbit to its original radius. The orbit is repeatable throughout the entire test. A force transducer, mounted in-line with the guide plate, measures the force between the ball and the guide plate, which directly relates to the friction coefficient. The SOT, shown in the figure, can operate in under ultra-high vacuum (10(exp -9) Torr) or in a variety of gases at atmospheric pressure. The load force can be adjusted between 45 and 450 N. By varying the load force and ball diameter, mean Hertzian stresses between 0.5 and 5.0 GPa can be obtained. The ball s orbital speed range is between 1 and 100 rpm.

  12. Backwards Spiral Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Astronomers using NASA's Hubble Space Telescope have found a spiral galaxy that may rotate in the opposite direction from what was expected.

    A picture of the oddball galaxy is available at http://heritage.stsci.edu or http://oposite.stsci.edu/pubinfo/pr/2002/03 or http://www.jpl.nasa.gov/images/wfpc . It was taken in May 2001 by Hubble's Wide Field and Planetary Camera 2, designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    The picture showed which side of galaxy NGC 4622 is closer to Earth; that information helped astronomers determine that the galaxy may be spinning clockwise. The image shows NGC 4622 and its outer pair of winding arms full of new stars, shown in blue.

    Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise.

    NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. Astronomers suspect this oddity was caused by the interaction of NGC 4622 with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a smaller companion galaxy.

    Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 lies 111 million light-years away in the direction of the constellation Centaurus.

    The science team, consisting of Drs. Ron Buta and Gene Byrd from the University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State

  13. Rebuilding Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    2005-01-01

    Major Observing Programme Leads to New Theory of Galaxy Formation Summary Most present-day large galaxies are spirals, presenting a disc surrounding a central bulge. Famous examples are our own Milky Way or the Andromeda Galaxy. When and how did these spiral galaxies form? Why do a great majority of them present a massive central bulge? An international team of astronomers [1] presents new convincing answers to these fundamental questions. For this, they rely on an extensive dataset of observations of galaxies taken with several space- and ground-based telescopes. In particular, they used over a two-year period, several instruments on ESO's Very Large Telescope. Among others, their observations reveal that roughly half of the present-day stars were formed in the period between 8,000 million and 4,000 million years ago, mostly in episodic burst of intense star formation occurring in Luminous Infrared Galaxies. From this and other evidence, the astronomers devised an innovative scenario, dubbed the "spiral rebuilding". They claim that most present-day spiral galaxies are the results of one or several merger events. If confirmed, this new scenario could revolutionise the way astronomers think galaxies formed. PR Photo 02a/05: Luminosity - Oxygen Abundance Relation for Galaxies (VLT) PR Photo 02b/05: The Spiral Rebuilding Scenario A fleet of instruments How and when did galaxies form? How and when did stars form in these island universes? These questions are still posing a considerable challenge to present-day astronomers. Front-line observational results obtained with a fleet of ground- and space-based telescopes by an international team of astronomers [1] provide new insights into these fundamental issues. For this, they embarked on an ambitious long-term study at various wavelengths of 195 galaxies with a redshift [2] greater than 0.4, i.e. located more than 4000 million light-years away. These galaxies were studied using ESO's Very Large Telescope, as well as the

  14. Spiral scan long object reconstruction through PI line reconstruction.

    PubMed

    Tam, K C; Hu, J; Sourbelle, K

    2004-06-01

    The response of a point object in a cone beam (CB) spiral scan is analysed. Based on the result, a reconstruction algorithm for long object imaging in spiral scan cone beam CT is developed. A region-of-interest (ROI) of the long object is scanned with a detector smaller than the ROI, and a portion of it can be reconstructed without contamination from overlaying materials. The top and bottom surfaces of the ROI are defined by two sets of PI lines near the two ends of the spiral path. With this novel definition of the top and bottom ROI surfaces and through the use of projective geometry, it is straightforward to partition the cone beam image into regions corresponding to projections of the ROI, the overlaying objects or both. This also simplifies computation at source positions near the spiral ends, and makes it possible to reduce radiation exposure near the spiral ends substantially through simple hardware collimation. Simulation results to validate the algorithm are presented. PMID:15248589

  15. Spiral viscous fingering.

    NASA Astrophysics Data System (ADS)

    Nagatsu, Yuichiro; Hayashi, Atsushi; Kato, Yoshihito; Tada, Yutaka

    2006-11-01

    When a less-viscous fluid displaces a more-viscous fluid in a radial Hele-Shaw cell, viscous fingering pattern is believed to develop in a radial direction. We performed experiments on viscous fingering in a radial Hele-Shaw cell when a polymer solution, a sodium polyacrylate (SPA) solution is used as the more-viscous fluid and the trivalent iron (Fe^3+) solution is as the less-viscous fluid. The experiment was done by varying the concentration of Fe^3+, cFe3+. We have found that viscous fingering pattern develops spirally when cFe3+ is larger than a threshold value, while the pattern develops in a radial direction for small cFe3+. We confirmed from different experiments that an instantaneous chemical reaction takes place between SPA solution and Fe^3+ solution. The chemical reaction produces precipitation and significantly reduces the viscosity of the SPA solution. The quantity of the precipitation is increased with cFe3+. We will make a discussion on the relationship between the formation of spiral viscous fingering and the chemical reaction taking place between the two fluids.

  16. CT Imaging: Basics and New Trends

    NASA Astrophysics Data System (ADS)

    Peyrin, Françoise; Engelke, Klaus

    This chapter presents the principle of X-ray CT and its evolution during the last 40 years. The first section describes the physical basis of X-ray CT, tomographic image reconstruction algorithms, and the source of artifacts in X-ray CT images. The second section is devoted to the evolution of CT technology from the first translation-rotation systems to multi-slice spiral CTs currently used today. The next section addresses specific developments of CT technology and applications, like perfusion CT, quantitative CT, and spectral CT. The fourth section introduces the problem of radiation exposure delivered to the patient and its evaluation. Finally the last section addresses the development in micro- and even nano-CT which is a rapidly evolving area in preclinical imaging and biology.

  17. SU-E-T-70: Commissioning a Multislice CT Scanner for X-Ray CT Polymer Gel Dosimetry

    SciTech Connect

    Johnston, H; Hilts, M; Jirasek, A

    2014-06-01

    Purpose: To commission a multislice computed tomography (CT) scanner for fast and reliable readout of radiation therapy (RT) dose distributions using CT polymer gel dosimetry (PGD). Methods: Commissioning was performed for a 16-slice CT scanner using images acquired through a 1L cylinder filled with water. Additional images were collected using a single slice machine for comparison purposes. The variability in CT number associated with the anode heel effect was evaluated and used to define a new slice-by-slice background image subtraction technique. Image quality was assessed for the multislice system by comparing image noise and uniformity to that of the single slice machine. The consistency in CT number across slices acquired simultaneously using the multislice detector array was also evaluated. Finally, the variability in CT number due to increasing x-ray tube load was measured for the multislice scanner and compared to the tube load effects observed on the single slice machine. Results: Slice-by-slice background subtraction effectively removes the variability in CT number across images acquired simultaneously using the multislice scanner and is the recommended background subtraction method when using a multislice CT system. Image quality for the multislice machine was found to be comparable to that of the single slice scanner. Further study showed CT number was consistent across image slices acquired simultaneously using the multislice detector array for each detector configuration of the slice thickness examined. In addition, the multislice system was found to eliminate variations in CT number due to increasing x-ray tube load and reduce scanning time by a factor of 4 when compared to imaging a large volume using a single slice scanner. Conclusion: A multislice CT scanner has been commissioning for CT PGD, allowing images of an entire dose distribution to be acquired in a matter of minutes. Funding support provided by the Natural Sciences and Engineering

  18. Spiral vane bioreactor

    NASA Technical Reports Server (NTRS)

    Morrison, Dennis R. (Inventor)

    1991-01-01

    A spiral vane bioreactor of a perfusion type is described in which a vertical chamber, intended for use in a microgravity condition, has a central rotating filter assembly and has flexible membranes disposed to rotate annularly about the filter assembly. The flexible members have end portions disposed angularly with respect to one another. A fluid replenishment medium is input from a closed loop liquid system to a completely liquid filled chamber containing microcarrier beads, cells and a fluid medium. Output of spent medium is to the closed loop. In the closed loop, the output and input parameters are sensed by sensors. A manifold permits recharging of the nutrients and pH adjustment. Oxygen is supplied and carbon dioxide and bubbles are removed and the system is monitored and controlled by a microprocessor.

  19. Arsia Mons Spiral Cloud

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the benefits of the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Extended Mission is the opportunity to observe how the planet's weather changes during a second full martian year. This picture of Arsia Mons was taken June 19, 2001; southern spring equinox occurred the same day. Arsia Mons is a volcano nearly large enough to cover the state of New Mexico. On this particular day (the first day of Spring), the MOC wide angle cameras documented an unusual spiral-shaped cloud within the 110 km (68 mi) diameter caldera--the summit crater--of the giant volcano. Because the cloud is bright both in the red and blue images acquired by the wide angle cameras, it probably consisted mostly of fine dust grains. The cloud's spin may have been induced by winds off the inner slopes of the volcano's caldera walls resulting from the temperature differences between the walls and the caldera floor, or by a vortex as winds blew up and over the caldera. Similar spiral clouds were seen inside the caldera for several days; we don't know if this was a single cloud that persisted throughout that time or one that regenerated each afternoon. Sunlight illuminates this scene from the left/upper left.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  20. Rejuvenation of spiral bulges

    NASA Astrophysics Data System (ADS)

    Thomas, Daniel; Davies, Roger L.

    2006-02-01

    indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudo-bulge formation must be restricted to spirals of types later than Sbc.

  1. Spiral Shock and Feathering Instability in Spiral Arms

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit

    2013-11-01

    A theoretical framework is developed to understand the feathering substructures along spiral arms by considering the perturbational gas response to a spiral shock. Feathers are density fluctuations that jut out from the spiral arm to the interarm region at large pitch angles. In a localized asymptotic approximation, related to the shearing sheet except that the inhomogeneities occur in space rather than in time, we derive the linearized perturbation equations for a razor-thin disk with turbulent interstellar gas, frozen-in magnetic field, and gaseous self-gravity. In the addition to the formulation, we investigate how individual normal modes of the system depend on seven dimensionless quantities that characterize the underlying time-independent axisymmetric state plus its steady, nonlinear, two-armed spiral-shock response to a hypothesized background density wave supported by the disk stars of the galaxy. In a particular case using galactic parameters at the inner part of M51 galaxy, we show that the normal mode with the maximum growth rate has the wavelength along the spiral arm that matches the observation of spacing of the feathers at around 500 pc. We also demonstrate that the self-gravity is an important parameter governing the feathering instability.

  2. Spiral Surface Growth without Desorption

    NASA Astrophysics Data System (ADS)

    Karma, Alain; Plapp, Mathis

    1998-11-01

    Spiral surface growth is well understood in the limit where the step motion is controlled by the local supersaturation of adatoms near the spiral ridge. In epitaxial thin-film growth, however, spirals can form in a step-flow regime where desorption of adatoms is negligible and the ridge dynamics is governed by the nonlocal diffusion field of adatoms on the whole surface. We investigate this limit numerically using a phase-field formulation of the Burton-Cabrera-Frank model, as well as analytically. Quantitative predictions, which differ strikingly from those of the local limit, are made for the selected step spacing as a function of the deposition flux, as well as for the dependence of the relaxation time to steady-state growth on the screw dislocation density.

  3. [Rational CT diagnosis before operations on the paranasal sinuses].

    PubMed

    Koitschev, A; Baumann, I; Remy, C T; Dammann, F

    2002-03-01

    Movement or metal artefacts as well as the relatively high radiation exposure of both the axial and the coronal scan are disadvantages of computed tomography. A single spiral CT scan with a secondary reformation replacing the second CT scan might solve these problems. The goal of this project was to compare the diagnostic value of primary spiral CT scans of paranasal sinuses with secondary reformations. These were evaluated by ENT surgeons as well as radiologists. We performed axial and coronal spiral-CT's of paranasal sinuses in 80 patients. The secondary coronal and axial reformations were calculated with 2 mm image sections. Although a reduced resolution was observed in the secondary reformations, this did not compromise the detection of important anatomical features. Image deterioration due to artifacts was significantly reduced. PMID:11975076

  4. Spirals in the Mandelbrot set I

    NASA Astrophysics Data System (ADS)

    Stephenson, John

    1994-04-01

    An explicit function is constructed to permit easy calculation of the asymptotic structure of the various spirals and branches around the main cardioid in the Mandelbrot set. Details of its application to “exterior” spirals are presented.

  5. Efficient Algorithm for Rectangular Spiral Search

    NASA Technical Reports Server (NTRS)

    Brugarolas, Paul; Breckenridge, William

    2008-01-01

    An algorithm generates grid coordinates for a computationally efficient spiral search pattern covering an uncertain rectangular area spanned by a coordinate grid. The algorithm does not require that the grid be fixed; the algorithm can search indefinitely, expanding the grid and spiral, as needed, until the target of the search is found. The algorithm also does not require memory of coordinates of previous points on the spiral to generate the current point on the spiral.

  6. Cardiac cone-beam CT volume reconstruction using ART

    SciTech Connect

    Nielsen, T.; Manzke, R.; Proksa, R.; Grass, M.

    2005-04-01

    Modern computed tomography systems allow volume imaging of the heart. Up to now, approximately two-dimensional (2D) and 3D algorithms based on filtered backprojection are used for the reconstruction. These algorithms become more sensitive to artifacts when the cone angle of the x-ray beam increases as it is the current trend of computed tomography (CT) technology. In this paper, we investigate the potential of iterative reconstruction based on the algebraic reconstruction technique (ART) for helical cardiac cone-beam CT. Iterative reconstruction has the advantages that it takes the cone angle into account exactly and that it can be combined with retrospective cardiac gating fairly easily. We introduce a modified ART algorithm for cardiac CT reconstruction. We apply it to clinical cardiac data from a 16-slice CT scanner and compare the images to those obtained with a current analytical reconstruction method. In a second part, we investigate the potential of iterative reconstruction for a large area detector with 256 slices. For the clinical cases, iterative reconstruction produces excellent images of diagnostic quality. For the large area detector, iterative reconstruction produces images superior to analytical reconstruction in terms of cone-beam artifacts.

  7. A rigid motion correction method for helical computed tomography (CT)

    NASA Astrophysics Data System (ADS)

    Kim, J.-H.; Nuyts, J.; Kyme, A.; Kuncic, Z.; Fulton, R.

    2015-03-01

    We propose a method to compensate for six degree-of-freedom rigid motion in helical CT of the head. The method is demonstrated in simulations and in helical scans performed on a 16-slice CT scanner. Scans of a Hoffman brain phantom were acquired while an optical motion tracking system recorded the motion of the bed and the phantom. Motion correction was performed by restoring projection consistency using data from the motion tracking system, and reconstructing with an iterative fully 3D algorithm. Motion correction accuracy was evaluated by comparing reconstructed images with a stationary reference scan. We also investigated the effects on accuracy of tracker sampling rate, measurement jitter, interpolation of tracker measurements, and the synchronization of motion data and CT projections. After optimization of these aspects, motion corrected images corresponded remarkably closely to images of the stationary phantom with correlation and similarity coefficients both above 0.9. We performed a simulation study using volunteer head motion and found similarly that our method is capable of compensating effectively for realistic human head movements. To the best of our knowledge, this is the first practical demonstration of generalized rigid motion correction in helical CT. Its clinical value, which we have yet to explore, may be significant. For example it could reduce the necessity for repeat scans and resource-intensive anesthetic and sedation procedures in patient groups prone to motion, such as young children. It is not only applicable to dedicated CT imaging, but also to hybrid PET/CT and SPECT/CT, where it could also ensure an accurate CT image for lesion localization and attenuation correction of the functional image data.

  8. The enigma of auroral spirals

    NASA Astrophysics Data System (ADS)

    Haerendel, G.

    One of the most spectacular forms that the aurora borealis can assume is the large-scale spiral Spirals are dominantly observed along the poleward boundary of the auroral oval during active periods Two concepts have been pursued in explaining their origin and in particular the counterclockwise sense of rotation of the luminous structures when viewed along the magnetic field direction An essentially magnetostatic theory following Hallinan 1976 attributes the spiral pattern to the twisting of field-lines caused by a centrally located upward field-aligned current According to Oguti 1981 and followers a clockwise rotation of the plasma flow produces the anticlockwise structure There are observations seemingly confirming or contradicting either theory In this paper it is argued that both concepts are insufficient in that only parts of the underlying physics are considered Besides field-aligned currents and plasma flow one has to take into at least two further aspects The ionospheric conductivity modified by particle precipitation has an impact on the magnetospheric plasma dynamics Furthermore auroral arcs are not fixed entities subject to distortions by plasma flows or twisted field-lines but sites of transient releases of energy We suggest that auroral spirals are ports of entry or exit of plasma into or out of the auroral oval This way it can be understood why a clockwise plasma flow can create an anticlockwise luminous pattern

  9. Spiral Galactic Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2009-05-01

    Before the period of galactic formation the uiverse consisted of a vast number of pre-formed systems consisting of two or more pre-galactic arms, the arms orbiting each other. As the orbits of the arms decayed the sides of the fore-sections of the arms tangentially collided and joined and thereby forming multi-armed spiral galaxies which began to rotate.The rotation resulted from the conversion of the orbital motion of the individual arms when joined into faster rotational motion of the newly formed galaxy. The spiral arms were maintained by the centripital force of the rapidly rotational motion of the galaxy system. As the rotational motion of the galaxy slowed down the arms of the spiral galaxy collapsed towards the body of the galaxy due to lessening of centripetal force on the arms and elliptical galaxies were formed and with further lessening of galactic rotational motion galactic disks were formed. One can see in galaxies M51, M100, NGC2336 and NGC4939 the galactic arms came from external orbit, not disks or instabilities in support of this theory. Also in support of this theory of galactic evolution is that spiral galaxies rotate faster than ellipticals or disks.

  10. Spiral tendency in blind flying

    NASA Technical Reports Server (NTRS)

    Carroll, Thomas; Mcavoy, William H

    1929-01-01

    The flight path followed by an airplane which was being flown by a blindfolded pilot was observed and recorded. When the pilot attempted to make a straight-away flight there was a tendency to deviate from the straight path and to take up a spiral one.

  11. VIBRATORY SPIRAL BLANCHER-COOLER

    EPA Science Inventory

    The objective of the demonstration project was to test the commercial feasibility of the vibratory spiral blancher-cooler, a newly designed steam blancher and air cooler that previous small scale tests showed could reduce the wasteload and energy consumption of preparing vegetabl...

  12. CT -- Body

    MedlinePlus

    ... News Physician Resources Professions Site Index A-Z Computed Tomography (CT) - Body Computed tomography (CT) of the body uses special x-ray ... Body? What is CT Scanning of the Body? Computed tomography, more commonly known as a CT or CAT ...

  13. CT Angiography after 20 Years

    PubMed Central

    Rubin, Geoffrey D.; Leipsic, Jonathon; Schoepf, U. Joseph; Fleischmann, Dominik; Napel, Sandy

    2015-01-01

    Through a marriage of spiral computed tomography (CT) and graphical volumetric image processing, CT angiography was born 20 years ago. Fueled by a series of technical innovations in CT and image processing, over the next 5–15 years, CT angiography toppled conventional angiography, the undisputed diagnostic reference standard for vascular disease for the prior 70 years, as the preferred modality for the diagnosis and characterization of most cardiovascular abnormalities. This review recounts the evolution of CT angiography from its development and early challenges to a maturing modality that has provided unique insights into cardiovascular disease characterization and management. Selected clinical challenges, which include acute aortic syndromes, peripheral vascular disease, aortic stent-graft and transcatheter aortic valve assessment, and coronary artery disease, are presented as contrasting examples of how CT angiography is changing our approach to cardiovascular disease diagnosis and management. Finally, the recently introduced capabilities for multispectral imaging, tissue perfusion imaging, and radiation dose reduction through iterative reconstruction are explored with consideration toward the continued refinement and advancement of CT angiography. PMID:24848958

  14. Power spiral conveyor section and method

    SciTech Connect

    Justice, J.C.; Delli-Gatti, F. Jr.

    1992-02-11

    This patent describes a method of mining a mine having a mine mouth, using a mining head with a spiral conveyor including a spiral conveyor screw rotatable with a shaft about an axis of rotation. It comprises: inserting the mining head in the mine through the mine mouth, and advancing the head into the mine mouth; continuously conveying mined material from the mine toward the mine mouth using the spiral conveyor; adding incremental lengths to the spiral conveyor screw as the distance from the mining head to the mouth increases; periodically providing power assists for effecting powered rotating of the spiral conveyor about its axis of rotation along the length of the spiral conveyor about its axis of rotation along the length of the spiral conveyor in the mine as the incremental lengths are added.

  15. Radiation dose evaluation in 64-slice CT examinations with adult and paediatric anthropomorphic phantoms

    PubMed Central

    Fujii, K; Aoyama, T; Yamauchi-Kawaura, C; Koyama, S; Yamauchi, M; Ko, S; Akahane, K; Nishizawa, K

    2009-01-01

    The objective of this study was to evaluate the organ dose and effective dose to patients undergoing routine adult and paediatric CT examinations with 64-slice CT scanners and to compare the doses with those from 4-, 8- and 16-multislice CT scanners. Patient doses were measured with small (<7 mm wide) silicon photodiode dosemeters (34 in total), which were implanted at various tissue and organ positions within adult and 6-year-old child anthropomorphic phantoms. Output signals from photodiode dosemeters were read on a personal computer, from which organ and effective doses were computed. For the adult phantom, organ doses (for organs within the scan range) and effective doses were 8–35 mGy and 7–18 mSv, respectively, for chest CT, and 12–33 mGy and 10–21 mSv, respectively, for abdominopelvic CT. For the paediatric phantom, organ and effective doses were 4–17 mGy and 3–7 mSv, respectively, for chest CT, and 5–14 mGy and 3–9 mSv, respectively, for abdominopelvic CT. Doses to organs at the boundaries of the scan length were higher for 64-slice CT scanners using large beam widths and/or a large pitch because of the larger extent of over-ranging. The CT dose index (CTDIvol), dose–length product (DLP) and the effective dose values using 64-slice CT for the adult and paediatric phantoms were the same as those obtained using 4-, 8- and 16-slice CT. Conversion factors of DLP to the effective dose by International Commission on Radiological Protection 103 were 0.024 mSv⋅mGy−1⋅cm−1 and 0.019 mSv⋅mGy−1⋅cm−1 for adult chest and abdominopelvic CT scans, respectively. PMID:19934069

  16. Radiation dose evaluation in 64-slice CT examinations with adult and paediatric anthropomorphic phantoms.

    PubMed

    Fujii, K; Aoyama, T; Yamauchi-Kawaura, C; Koyama, S; Yamauchi, M; Ko, S; Akahane, K; Nishizawa, K

    2009-12-01

    The objective of this study was to evaluate the organ dose and effective dose to patients undergoing routine adult and paediatric CT examinations with 64-slice CT scanners and to compare the doses with those from 4-, 8- and 16-multislice CT scanners. Patient doses were measured with small (<7 mm wide) silicon photodiode dosemeters (34 in total), which were implanted at various tissue and organ positions within adult and 6-year-old child anthropomorphic phantoms. Output signals from photodiode dosemeters were read on a personal computer, from which organ and effective doses were computed. For the adult phantom, organ doses (for organs within the scan range) and effective doses were 8-35 mGy and 7-18 mSv, respectively, for chest CT, and 12-33 mGy and 10-21 mSv, respectively, for abdominopelvic CT. For the paediatric phantom, organ and effective doses were 4-17 mGy and 3-7 mSv, respectively, for chest CT, and 5-14 mGy and 3-9 mSv, respectively, for abdominopelvic CT. Doses to organs at the boundaries of the scan length were higher for 64-slice CT scanners using large beam widths and/or a large pitch because of the larger extent of over-ranging. The CT dose index (CTDI(vol)), dose-length product (DLP) and the effective dose values using 64-slice CT for the adult and paediatric phantoms were the same as those obtained using 4-, 8- and 16-slice CT. Conversion factors of DLP to the effective dose by International Commission on Radiological Protection 103 were 0.024 mSvmGy(-1)cm(-1) and 0.019 mSvmGy(-1)cm(-1) for adult chest and abdominopelvic CT scans, respectively. PMID:19934069

  17. Multiferroics with spiral spin orders.

    PubMed

    Tokura, Yoshinori; Seki, Shinichiro

    2010-04-12

    Cross correlation between magnetism and electricity in a solid can host magnetoelectric effects, such as magnetic (electric) induction of polarization (magnetization). A key to attain the gigantic magnetoelectric response is to find the efficient magnetism-electricity coupling mechanisms. Among those, recently the emergence of spontaneous (ferroelectric) polarization in the insulating helimagnet or spiral-spin structure was unraveled, as mediated by the spin-exchange and spin-orbit interactions. The sign of the polarization depends on the helicity (spin rotation sense), while the polarization direction itself depends on further details of the mechanism and the underlying lattice symmetry. Here, we describe some prototypical examples of the spiral-spin multiferroics, which enable some unconventional magnetoelectric control such as the magnetic-field-induced change of the polarization direction and magnitude as well as the electric-field-induced change of the spin helicity and magnetic domain. PMID:20496385

  18. Planet Masses from Disk Spirals

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-12-01

    Young, forming planets can generate immense spiral structures within their protoplanetary disks. A recent study has shown that observations of these spiral structures may allow astronomers to measure the mass of the planets that create them.Spirals From WavesSnapshots of the surface density of a protoplanetary disk in a 2D simulation, 3D simulation, and synthesized scattered-light image. Click for a closer look! [Fung Dong, 2015]Recent studies have shown that a single planet, if it is massive enough, can excite multiple density waves within a protoplanetary disk as it orbits. These density waves can then interfere to produce a multiple-armed spiral structure in the disk inside of the planets orbit a structure which can potentially be observed in scattered-light images of the disk.But what do these arms look like, and what factors determine their structure? In a recently published study, Jeffrey Fung and Ruobing Dong, two researchers at the University of California at Berkeley, have modeled the spiral arms in an effort to answer these questions.Arms Provide AnswersA useful parameter for describing the structure is the azimuthal separation (sep) between the primary and secondary spiral arms. If you draw a circle within the disk and measure the angle between the two points where the primary and secondary arms cross it, thats sep.Azimuthal separation of the primary and secondary spiral arms, as a function of the planet-to-star mass ratio q. The different curves represent different disk aspect ratios. [Fung Dong, 2015]The authors find thatsep stays roughly constant for different radii, but its strongly dependent on the planets mass: for larger planets, sep increases. They discover that sep scales as a power of the planet mass for companions between Neptune mass and 16 Jupiter masses, orbiting around a solar-mass star. For larger, brown-dwarf-size companions, sep is a constant 180.If this new theory is confirmed, it could have very interesting implications for

  19. Spiralling dynamics near heteroclinic networks

    NASA Astrophysics Data System (ADS)

    Rodrigues, Alexandre A. P.; Labouriau, Isabel S.

    2014-02-01

    There are few explicit examples in the literature of vector fields exhibiting complex dynamics that may be proved analytically. We construct explicitly a two parameter family of vector fields on the three-dimensional sphere S, whose flow has a spiralling attractor containing the following: two hyperbolic equilibria, heteroclinic trajectories connecting them transversely and a non-trivial hyperbolic, invariant and transitive set. The spiralling set unfolds a heteroclinic network between two symmetric saddle-foci and contains a sequence of topological horseshoes semiconjugate to full shifts over an alphabet with more and more symbols, coexisting with Newhouse phenomena. The vector field is the restriction to S of a polynomial vector field in R. In this article, we also identify global bifurcations that induce chaotic dynamics of different types.

  20. M51's spiral structure

    NASA Technical Reports Server (NTRS)

    Howard, S.; Byrd, Gene G.

    1990-01-01

    The M51 system (NGC 5194/5195) provides an excellent problem both in spiral structure and in galaxy interactions. The authors present an analytic study of a computer experiment on the excitation mechanisms for M51's spiral arms and whether or not a halo is important for these mechanisms. This work extends previous numerical studies of the M51 system by including self-gravitation in a two component disk: gas and stars, and a dark halo. The analytic study provides two new observational constraints: the time (approx. 70 to 84 million years ago) and position angle of perigalacticon (300 degrees). By using these constraints and a simple conic approximation, the search for the companion's possible orbit is greatly simplified. This requires fewer N-body simulations than a fully self-gravitating orbit search.

  1. Application of fast radon transform to CT scanners: difficulties and solutions

    NASA Astrophysics Data System (ADS)

    Mitra, Abhishek; Banerjee, Swapna

    2007-03-01

    As a tomographic reconstruction algorithm, the recently proposed "Fast Radon Transform" (FRT) has some computational advantages. To prove its practical importance the technical difficulties associated with its application to fan-beam CT scanners as well as Spiral/Helical CT system are solved here. Some techniques are described to convert the actual fan-beam data or the spiral/helical CT data to parallel-beam data required for the FRT algorithm in order to reconstruct the CT images. Simulation results are presented to validate the complete method.

  2. THE SPIRAL GALAXY M100

    NASA Technical Reports Server (NTRS)

    2002-01-01

    An image of the grand design of spiral galaxy M100 obtained with NASA's Hubble Space Telescope resolves individual stars within the majestic spiral arms. (These stars typically appeared blurred together when viewed with ground-based telescopes.) Hubble has the ability to resolve individual stars in other galaxies and measure accurately the light from very faint stars. This makes space telescope invaluable for identifying a rare class of pulsating stars, called Cepheid Variable stars embedded within M100's spiral arms. Cepheids are reliable cosmic distance mileposts. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years. M100 (100th object in the Messier catalog of non-stellar objects) is a majestic face-on spiral galaxy. It is a rotating system of gas and stars, similar to our own galaxy, the Milky Way. Hubble routinely can view M100 with a level of clarity and sensitivity previously possible only for the very few nearby galaxies that compose our 'Local Group.'' M100 is a member of the huge Virgo cluster of an estimated 2,500 galaxies. The galaxy can be seen by amateur astronomers as a faint, pinwheel-shaped object in the spring constellation Coma Berenices. Technical Information: The Hubble Space Telescope image was taken on December 31, 1993 with the Wide Field Planetary Camera 2 (WFPC 2). This color picture is a composite of several images taken in different colors of light. Blue corresponds to regions containing hot newborn stars. The Wide Field and Planetary Camera 2 was developed by the Jet Propulsion Laboratory (JPL) and managed by the Goddard Space Flight Center for NASA's Office of Space Science. Credit: J. Trauger, JPL and NASA

  3. Saved by a Spiral Notebook

    ERIC Educational Resources Information Center

    Taylor, Kristan

    2005-01-01

    In this article, the author shares how she used journal exercises to unify her classroom. Students used cheap spiral notebooks and followed a few very basic rules: (1) Start out by writing for 5 minutes, increasing to 15 or more; (2) Read the entry to the class only if you want to; and (3) Use the given topic or write whatever is on your mind.…

  4. Spiral inertial waves emitted from geophysical vortices

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Özgökmen, Tamay M.

    2016-03-01

    By numerically simulating an initially unstable geophysical vortex, we discover for the first time a special kind of inertial waves, which are emitted in a spiral manner from the vortices; we refer to these waves as spiral inertial waves (SIWs). SIWs appear at small Rossby numbers (0.01 ≤ Ro ≤ 1) according to our parameter sweep experiments; the amplitude, wavelength and frequency of SIWs are sensitive to Rossby numbers. We extend the Lighthill-Ford radiation into inertial waves, and propose an indicator for the emission of inertial waves; this indicator may be adopted into general circulation models to parameterize inertial waves. Additionally, in our tracer releasing experiments, SIWs organize tracers into spirals, and modify the tracer's local rate of change by advecting tracers vertically. Further, the spirals of SIWs resembles some spiral features observed in the ocean and atmosphere, such as spiral ocean eddies and spiral hurricane rainbands; thus, SIWs may offer another mechanism to form spiral eddies and rainbands. Since no density anomaly is required to generate the spirals of SIWs, we infer that the density anomaly, hence the baroclinic or frontal instability, is unlikely to be the key factor in the formation of these spiral features.

  5. Transient spirals as superposed instabilities

    SciTech Connect

    Sellwood, J. A.; Carlberg, R. G. E-mail: carlberg@astro.utoronto.ca

    2014-04-20

    We present evidence that recurrent spiral activity, long manifested in simulations of disk galaxies, results from the superposition of a few transient spiral modes. Each mode lasts between 5 and 10 rotations at its corotation radius where its amplitude is greatest. The scattering of stars as each wave decays takes place over narrow ranges of angular momentum, causing abrupt changes to the impedance of the disk to subsequent traveling waves. Partial reflections of waves at these newly created features allows new standing-wave instabilities to appear that saturate and decay in their turn, scattering particles at new locations, creating a recurring cycle. The spiral activity causes the general level of random motion to rise, gradually decreasing the ability of the disk to support further activity unless the disk contains a dissipative gas component from which stars form on near-circular orbits. We also show that this interpretation is consistent with the behavior reported in other recent simulations with low-mass disks.

  6. Collective excitations in itinerant spiral magnets

    SciTech Connect

    Kampf, A.P.

    1996-01-01

    We investigate the coupled charge and spin collective excitations in the spiral phases of the two-dimensional Hubbard model using a generalized random-phase approximation. Already for small doping the spin-wave excitations are strongly renormalized due to low-energy particle-hole excitations. Besides the three Goldstone modes of the spiral state the dynamical susceptibility reveals an extra zero mode for low doping and strong coupling values signaling an intrinsic instability of the homogeneous spiral state. In addition, near-zero modes are found in the vicinity of the spiral pitch wave number for out-of-plane spin fluctuations. Their origin is found to be the near degeneracy with staggered noncoplanar spiral states which, however, are not the lowest energy Hartree-Fock solutions among the homogeneous spiral states. {copyright} {ital 1996 The American Physical Society.}

  7. CT Scans

    MedlinePlus

    ... cross-sectional pictures of your body. Doctors use CT scans to look for Broken bones Cancers Blood clots Signs of heart disease Internal bleeding During a CT scan, you lie still on a table. The table ...

  8. Optical fiber antenna generating spiral beam shapes

    SciTech Connect

    Sarkar Pal, S.; Mondal, S. K. Kumar, R.; Akula, A.; Ghosh, R.; Bhatnagar, R.; Kumbhakar, D.

    2014-01-20

    A simple method is proposed here to generate vortex beam and spiral intensity patterns from a Gaussian source. It uses a special type of optical fiber antenna of aperture ∼80 nm having naturally grown surface curvature along its length. The antenna converts linearly polarized Gaussian beam into a beam with spiral intensity patterns. The experimentally obtained spiral patterns with single and double spiral arms manifest the orbital angular momentum, l = ±1, 2, carried by the output beam. Such beam can be very useful for optical tweezer, metal machining, and similar applications.

  9. Recent manufacturing advances for spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Bill, Robert C.

    1991-01-01

    The U.S. Army Aviation Systems Command (AVSCOM), through the Propulsion Directorate at NASA LRC, has recently sponsored projects to advance the manufacturing process for spiral bevel gears. This type of gear is a critical component in rotary-wing propulsion systems. Two successfully completed contracted projects are described. The first project addresses the automated inspection of spiral bevel gears through the use of coordinate measuring machines. The second project entails the computer-numerical-control (CNC) conversion of a spiral bevel gear grinding machine that is used for all aerospace spiral bevel gears. The results of these projects are described with regard to the savings effected in manufacturing time.

  10. Recent manufacturing advances for spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Bill, Robert C.

    1991-01-01

    The U.S. Army Aviation Systems Command (AVSCOM), through the Propulsion Directorate at NASA Lewis Research Center, has recently sponsored projects to advance the manufacturing process for spiral bevel gears. This type of gear is a critical component in rotary-wing propulsion systems. Two successfully completed contracted projects are described. The first project addresses the automated inspection of spiral bevel gears through the use of coordinate measuring machines. The second project entails the computer-numerical-control (CNC) conversion of a spiral bevel gear grinding machine that is used for all aerospace spiral bevel gears. The results of these projects are described with regard to the savings effected in manufacturing time.

  11. Translational Symmetry-Breaking for Spiral Waves

    NASA Astrophysics Data System (ADS)

    LeBlanc, V. G.; Wulff, C.

    2000-10-01

    Spiral waves are observed in numerous physical situations, ranging from Belousov-Zhabotinsky (BZ) chemical reactions, to cardiac tissue, to slime-mold aggregates. Mathematical models with Euclidean symmetry have recently been developed to describe the dynamic behavior (for example, meandering) of spiral waves in excitable media. However, no physical experiment is ever infinite in spatial extent, so the Euclidean symmetry is only approximate. Experiments on spiral waves show that inhomogeneities can anchor spirals and that boundary effects (for example, boundary drifting) become very important when the size of the spiral core is comparable to the size of the reacting medium. Spiral anchoring and boundary drifting cannot be explained by the Euclidean model alone. In this paper, we investigate the effects on spiral wave dynamics of breaking the translation symmetry while keeping the rotation symmetry. This is accomplished by introducing a small perturbation in the five-dimensional center bundle equations (describing Hopf bifurcation from one-armed spiral waves) which is SO(2)-equivariant but not equivariant under translations. We then study the effects of this perturbation on rigid spiral rotation, on quasi-periodic meandering and on drifting.

  12. Disk's Spiral Arms Point to Possible Planets

    NASA Video Gallery

    Simulations of young stellar systems suggest that planets embedded in a circumstellar disk can produce many distinctive structures, including rings, gaps and spiral arms. This video compares comput...

  13. Emergency Physicians Think in Spirals

    PubMed Central

    Renouf, Tia; Whalen, Desmond; Pollard, Megan

    2015-01-01

    As adult learners, junior clerks on core rotations in emergency medicine (EM) are expected to “own” their patients and follow them from presentation to disposition in the Emergency Department (ED). Traditionally, we teach clerks to present an exhaustive linear list of symptoms and signs to their preceptors. This does not apply well to the fast-paced ED setting. Mnemonics have been developed to teach clerks how to present succinctly and cohesively. To address the need for continual patient reassessment throughout the patient’s journey in the ED, we propose a complimentary approach called SPIRAL. PMID:26719824

  14. HUBBLE REVEALS 'BACKWARDS' SPIRAL GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have found a spiral galaxy that may be spinning to the beat of a different cosmic drummer. To the surprise of astronomers, the galaxy, called NGC 4622, appears to be rotating in the opposite direction to what they expected. Pictures by NASA's Hubble Space Telescope helped astronomers determine that the galaxy may be spinning clockwise by showing which side of the galaxy is closer to Earth. A Hubble telescope photo of the oddball galaxy is this month's Hubble Heritage offering. The image shows NGC 4622 and its outer pair of winding arms full of new stars [shown in blue]. Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise. NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. What caused this galaxy to behave differently from most galaxies? Astronomers suspect that NGC 4622 interacted with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a small companion galaxy. The galaxy's core provides new evidence for a merger between NGC 4622 and a smaller galaxy. This information could be the key to understanding the unusual leading arms. Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way Galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 resides 111 million light-years away in the constellation Centaurus. The pictures were taken in May 2001 with Hubble

  15. Magnetic fields in nearby spirals

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohui; Lenc, Emil

    2013-10-01

    Magnetic fields play an important role in star formation process and dynamic evolution of galaxies. Previous studies of magnetic fields relied on narrow band polarisation observations and difficult to disentangle magnetised structures along line of sight. Thanks to the broad bandwidth and multi-channels of CABB we are now able to recover the 3D structures of magnetic fields using RM synthesis and QU-fitting. We propose to observe two nearby spirals M83 and NGC 4945 to build clear pictures of their magnetic fields.

  16. Cervix carcinoma and incidental finding of medullary thyroid carcinoma by 18F-FDG PET/CT--clinical case.

    PubMed

    Chaushev, Borislav; Bochev, Pavel; Klisarova, Anelia; Yordanov, Kaloyan; Encheva, Elitsa; Dancheva, Jivka; Yordanova, Cvetelina; Hristozov, Kiril; Krasnaliev, Ivan; Radev, Radoslav; Nenkov, Rumen

    2014-01-01

    Thyroid nodules are encountered in clinical practice during the diagnostic procedures or patients' follow-up due to other diseases quite far from the thyroid gland with prevalence 4-50% in general population, depending on age, diagnostic method and race. The prevalence of thyroid nodules increases with age and their clarification should be done for their adequate treatment. An 18F-FDG PET/CT was done with a PET/CT scanner (Philips Gemini TF), consisting of dedicated lutetium orthosilicate full ring PET scanner and 16 slice CT. The PET/CT scan of the whole-body revealed on the CT portion a hypodense nodular lesion in the left lobe of the thyroid gland with increased uptake of 18F-FDG on the PET with SUVmax 10.3 and demonstrated a complete response to the induction therapy of the main oncological disease of the patient--squamous cell carcinoma. This clinical case demonstrates that whole-body 18F-FDG-PET/CT has an increasingly important role in the early evaluation of thyroid cancer as a second independent malignant localization. Focal thyroid lesion with high risk of thyroid malignancy was incidentally found on 18F-FDG PET/CT. PMID:25088110

  17. Slow bars in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Khoruzhii, O. V.

    2000-11-01

    Here we put forward some arguments in favour of the existence of slow bars. More then a half of spiral galaxies have in their central regions a bar - a structure in the form of triaxial ellipsoid. Historically two models of the bar were developed - those of the so called ``slow'' and ``fast'' bars. In both cases the bar is in some resonance with the galactic disc region near the bar ends - it is the corotation resonance for a fast bar and the inner Lindblad resonance for a slow bar. For the same angular velocity the fast bar would be larger then the slow bar. Alternatively, for the same size the fast bar would have much higher angular velocity, that being the reason for the terminology used. Up till now, the direct measurement of angular velocity of a bar has been an open problem. This is why all arguments on the nature of bar observed in some particular galaxy are inevitably indirect. Despite the fact that the model of slow bars was developed slightly earlier, the main part of attention was focused on the fast bars. Presently many researchers believe in the existence of the fast bars in real galaxies, while discussions on the existence of the slow bars continue so far. In this Letter we demonstrate that the bar detected in the grand design spiral galaxy NGC 157 is the slow bar.

  18. Generation and characterization of spirally polarized fields

    NASA Astrophysics Data System (ADS)

    Ramírez-Sánchez, V.; Piquero, G.; Santarsiero, M.

    2009-08-01

    Recently introduced global parameters for describing the polarization of a beam are used to characterize spirally polarized fields, which include as particular cases azimuthally and radially polarized fields. Theoretical predictions about such global parameters are experimentally confirmed by generating beams with spirally polarized transverse patterns, by means of two different procedures.

  19. 29 CFR 1917.121 - Spiral stairways.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 7 2010-07-01 2010-07-01 false Spiral stairways. 1917.121 Section 1917.121 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (CONTINUED) MARINE TERMINALS Terminal Facilities § 1917.121 Spiral stairways. (a) Definition....

  20. The smallest fullerene without a spiral

    NASA Astrophysics Data System (ADS)

    Brinkmann, Gunnar; Goedgebeur, Jan; McKay, Brendan D.

    2012-01-01

    In this note, we give the result of a computer search for the smallest fullerene that does not allow a face spiral code as used by Manolopoulos and Fowler and adopted in IUPAC recommendations for fullerene nomenclature. The search enumerated all the small fullerenes on up to 400 vertices and the conclusion is that the smallest fullerene without a face spiral has 380 vertices.

  1. Twokink excitation in a spiral magnetic structure

    NASA Astrophysics Data System (ADS)

    Kiselev, V. V.; Raskovalov, A. A.

    2016-01-01

    Twokink excitations in the spiral structures of magnets and multiferroics are found and analyzed within the framework for the sine-Gordon model. It is shown that the movement and interaction of the kinks is accompanied by macroscopic translations of the spiral structure. The ways of observing and exciting kinks in the external magnetic field are discussed.

  2. 29 CFR 1917.121 - Spiral stairways.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 7 2011-07-01 2011-07-01 false Spiral stairways. 1917.121 Section 1917.121 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (CONTINUED) MARINE TERMINALS Terminal Facilities § 1917.121 Spiral stairways. (a) Definition....

  3. Spiral density waves in M81. I. Stellar spiral density waves

    SciTech Connect

    Feng, Chien-Chang; Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Taam, Ronald E.

    2014-04-20

    Aside from the grand-design stellar spirals appearing in the disk of M81, a pair of stellar spiral arms situated well inside the bright bulge of M81 has been recently discovered by Kendall et al. The seemingly unrelated pairs of spirals pose a challenge to the theory of spiral density waves. To address this problem, we have constructed a three-component model for M81, including the contributions from a stellar disk, a bulge, and a dark matter halo subject to observational constraints. Given this basic state for M81, a modal approach is applied to search for the discrete unstable spiral modes that may provide an understanding for the existence of both spiral arms. It is found that the apparently separated inner and outer spirals can be interpreted as a single trailing spiral mode. In particular, these spirals share the same pattern speed 25.5 km s{sup –1} kpc{sup –1} with a corotation radius of 9.03 kpc. In addition to the good agreement between the calculated and the observed spiral pattern, the variation of the spiral amplitude can also be naturally reproduced.

  4. Electrodynamics of planar Archimedean spiral resonator

    NASA Astrophysics Data System (ADS)

    Maleeva, N.; Averkin, A.; Abramov, N. N.; Fistul, M. V.; Karpov, A.; Zhuravel, A. P.; Ustinov, A. V.

    2015-07-01

    We present a theoretical and experimental study of electrodynamics of a planar spiral superconducting resonator of a finite length. The resonator is made in the form of a monofilar Archimedean spiral. By making use of a general model of inhomogeneous alternating current flowing along the resonator and specific boundary conditions on the surface of the strip, we obtain analytically the frequencies fn of resonances which can be excited in such system. We also calculate corresponding inhomogeneous RF current distributions ψ n ( r ) , where r is the coordinate across a spiral. We show that the resonant frequencies and current distributions are well described by simple relationships f n = f 1 n and ψ n ( r ) ≃ sin [ π n ( r / R e ) 2 ] , where n = 1 , 2... and Re is the external radius of the spiral. Our analysis of electrodynamic properties of spiral resonators' is in good agreement with direct numerical simulations and measurements made using specifically designed magnetic probe and laser scanning microscope.

  5. Bifurcations and Dynamics of Spiral Waves

    NASA Astrophysics Data System (ADS)

    Sandstede, B.; Scheel, A.; Wulff, P. C.

    1999-08-01

    . In this article, it is shown that the dynamics near meandering spiral waves or other patterns is determined by a finite-dimensional vector field that has a certain skew-product structure over the group SE SE(N) . This generalizes our earlier work on center-manifold theory near rigidly rotating spiral waves to meandering spirals. In particular, for meandering spirals, it is much more sophisticated to extract the aforementioned skew-product structure since spatio-temporal rather than only spatial symmetries have to be accounted for. Another difficulty is that the action of the Euclidean symmetry group on the underlying function space is not differentiable, and in fact may be discontinuous. Using this center-manifold reduction, Hopf bifurcations and periodic forcing of spiral waves are then investigated. The results explain the transitions to patterns with two or more temporal frequencies that have been observed in various experiments and numerical simulations.

  6. Head CT scan

    MedlinePlus

    Brain CT; Cranial CT; CT scan - skull; CT scan - head; CT scan - orbits; CT scan - sinuses; Computed tomography - cranial ... or other growth (mass) Cerebral atrophy (loss of brain tissue) ... with the hearing nerve Stroke or transient ischemic attack (TIA)

  7. Automatic phase determination for retrospectively gated cardiac CT

    SciTech Connect

    Manzke, R.; Koehler, Th.; Nielsen, T.; Hawkes, D.; Grass, M.

    2004-12-01

    The recent improvements in CT detector and gantry technology in combination with new heart rate adaptive cone beam reconstruction algorithms enable the visualization of the heart in three dimensions at high spatial resolution. However, the finite temporal resolution still impedes the artifact-free reconstruction of the heart at any arbitrary phase of the cardiac cycle. Cardiac phases must be found during which the heart is quasistationary to obtain outmost image quality. It is challenging to find these phases due to intercycle and patient-to-patient variability. Electrocardiogram (ECG) information does not always represent the heart motion with an adequate accuracy. In this publication, a simple and efficient image-based technique is introduced which is able to deliver stable cardiac phases in an automatic and patient-specific way. From low-resolution four-dimensional data sets, the most stable phases are derived by calculating the object similarity between subsequent phases in the cardiac cycle. Patient-specific information about the object motion can be determined and resolved spatially. This information is used to perform optimized high-resolution reconstructions at phases of little motion. Results based on a simulation study and three real patient data sets are presented. The projection data were generated using a 16-slice cone beam CT system in low-pitch helical mode with parallel ECG recording.

  8. Radiochromic films for dental CT dosimetry: a feasibility study.

    PubMed

    Rampado, O; Bianchi, S D; Peruzzo Cornetto, A; Rossetti, V; Ropolo, R

    2014-02-01

    Dental CT dose evaluations are commonly performed using thermoluminescent dosimeters (TLD) inside anthropomorphic phantoms. Radiochromic films with good sensitivity in the X-ray diagnostic field have recently been developed and are commercially available as GAFCHROMIC XR-QA. There are potential advantages in the use of radiochromic films such as a more comprehensive dosimetry thanks to the adjustable size of the film samples. The purpose of this study was to investigate the feasibility of using radiochromic films for dental CT dose evaluations. Film samples were cut with a width of 5mm and a length of 25 mm (strips), the same size as the Alderson Rando anthropomorphic phantom holes used in this study. Dental CT dose measurements were performed using simultaneously both TLD and radiochromic strips in the same phantom sites. Two equipment types were considered for dental CT examinations: a 16 slice CT and a cone beam CT. Organ equivalent doses were then obtained averaging the measurements from the sites of the same organ and effective doses were calculated using ICRP 103 weighting factors. The entire procedure was repeated four times for each CT in order to compare also the repeatability of the two dosimeter types. A linear correlation was found between the absorbed dose evaluated with radiochromic films and with TLD, with slopes of 0.930 and 0.944 (correlation r>0.99). The maximum difference between the two dosimeter's measurements was 25%, whereas the average difference was 7%. The measurement repeatability was comparable for the two dosimeters at cumulative doses above 15 mGy (estimated uncertainty at 1 sigma level of about 5%), whereas below this threshold radiochromic films show a greater dispersion of data, of about 10% at 1 sigma level. We obtained, using respectively Gafchromic and TLD measurements, effective dose values of 107 μSv and 117 μSv (i.e. difference of 8.6%) for the cone beam CT and of 523 μSv and 562 μSv (i.e. difference of 7%) for the

  9. Spiral slotted phased antenna array

    NASA Technical Reports Server (NTRS)

    Ellis, H., Jr. (Inventor)

    1982-01-01

    A flush mounting, cavity-backed, dual orthogonal slot antenna for aircraft and space vehicles is described. Improved radiation pattern characteristics are obtained by making the spiral slot pattern elliptical in the aperture plane. A cavity and a flanged aperture plate are configured such that one slot pair is orthogonal with respect to another slot pair within the aperture plate. Coaxial split-tube baluns are used to drive the junctions between corresponding slot pairs. An optional cavity dielectric is provided and a drive coupling arrangement includes a four port comparator hybrid having sum and difference ports respectively, for alternate excitation to produce a single lobe or a double lobe pattern with null. Switching apparatus is provided to connect a common terminal to either of the ports.

  10. Low-Noise Spiral Bevel Gears

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.; Handschuh, Robert F.; Coy, John J.; Henry, Zachary; Thomas, John; Litvin, Faydor L.

    1994-01-01

    Modified spiral bevel gears that generate relatively little noise and vibration designed and fabricated for use in U.S. Army OH-58D helicopter. Noise reduced by 12 to 19 dB. Similar low-noise, low-vibration spiral bevel gears used in other helicopters, with consequent benefits in comfort and health of pilots and passengers, enhancement of pilots' performance and safety through reduction of audible distraction, and reduction in cost and weight of helicopters through reduction in amount of sound-proofing material. Low-noise, low-vibration spiral bevel gears also used in drive axles of cars and trucks for smoother, quieter rides.

  11. Pitch angle of galactic spiral arms

    SciTech Connect

    Michikoshi, Shugo; Kokubo, Eiichiro E-mail: kokubo@th.nao.ac.jp

    2014-06-01

    One of the key parameters that characterizes spiral arms in disk galaxies is a pitch angle that measures the inclination of a spiral arm to the direction of galactic rotation. The pitch angle differs from galaxy to galaxy, which suggests that the rotation law of galactic disks determines it. In order to investigate the relation between the pitch angle of spiral arms and the shear rate of galactic differential rotation, we perform local N-body simulations of pure stellar disks. We find that the pitch angle increases with the epicycle frequency and decreases with the shear rate and obtain the fitting formula. This dependence is explained by the swing amplification mechanism.

  12. Explosions in Majestic Spiral Beauties

    NASA Astrophysics Data System (ADS)

    2004-12-01

    Images of beautiful galaxies, and in particular of spiral brethren of our own Milky Way, leaves no-one unmoved. It is difficult indeed to resist the charm of these impressive grand structures. Astronomers at Paranal Observatory used the versatile VIMOS instrument on the Very Large Telescope to photograph two magnificent examples of such "island universes", both of which are seen in a southern constellation with an animal name. But more significantly, both galaxies harboured a particular type of supernova, the explosion of a massive star during a late and fatal evolutionary stage. The first image (PR Photo 33a/04) is of the impressive spiral galaxy NGC 6118 [1], located near the celestial equator, in the constellation Serpens (The Snake). It is a comparatively faint object of 13th magnitude with a rather low surface brightness, making it pretty hard to see in small telescopes. This shyness has prompted amateur astronomers to nickname NGC 6118 the "Blinking Galaxy" as it would appear to flick into existence when viewed through their telescopes in a certain orientation, and then suddenly disappear again as the eye position shifted. There is of course no such problem for the VLT's enormous light-collecting power and ability to produce sharp images, and this magnificent galaxy is here seen in unequalled detail. The colour photo is based on a series of exposures behind different optical filters, obtained with the VIMOS multi-mode instrument on the 8.2-m VLT Melipal telescope during several nights around August 21, 2004. About 80 million light-years away, NGC 6118 is a grand-design spiral seen at an angle, with a very small central bar and several rather tightly wound spiral arms (it is classified as of type "SA(s)cd" [2]) in which large numbers of bright bluish knots are visible. Most of them are active star-forming regions and in some, very luminous and young stars can be perceived. Of particular interest is the comparatively bright stellar-like object situated directly

  13. Evaluation of a low-dose/slow-rotating SPECT-CT system

    NASA Astrophysics Data System (ADS)

    Hamann, M.; Aldridge, M.; Dickson, J.; Endozo, R.; Lozhkin, K.; Hutton, B. F.

    2008-05-01

    The 4-slice CT that forms part of the GE Infinia Hawkeye-4 SPECT-CT scanner (Hawkeye) is evaluated against the diagnostic 16-slice CT that is incorporated in the GE Discovery ST PET-CT system (DST). The x-ray tube of the slow-rotating Hawkeye system (23 s/rotation) operates at approximately a third of the dose of diagnostic systems as used for conventional diagnostic imaging. Image reconstruction is optimized for low noise. High-contrast spatial resolution significantly falls behind diagnostic figures: the average of MTF50 and MTF10 (resolution where the MTF has fallen to 50% and 10%) is 2.8 ± 0.1 cm-1 for Hawkeye and 5.3 ± 0.1 cm-1 for the DST (standard reconstruction filters). Resolution in the direction of the couch movement (z coordinate) is governed by the fixed Hawkeye slice width of 5 mm. Reconstruction accuracy is found to be increased by reducing the default z increment from 4.4 mm to 2.2 mm. Low-contrast object detectability is superior compared with diagnostic systems operating in the Hawkeye dose range. In the diagnostic dose regime, however, small low-contrast details remain visible in DST that are not detectable with Hawkeye. Although not of diagnostic quality, the low-dose Hawkeye provides appropriate data for SPECT attenuation correction and anatomical localization capability. For more information on this article, see medicalphysicsweb.org

  14. Clinical count rate performance of an LSO PET/CT scanner utilizing a new front-end electronics architecture with sub-nanosecond intrinsic timing resolution

    NASA Astrophysics Data System (ADS)

    Carney, J. P. J.; Townsend, D. W.

    2006-12-01

    A new front-end electronics architecture with sub-nanosecond intrinsic timing resolution has recently been incorporated into a 16 slice LSO PET/CT scanner for imaging applications in oncology. The new electronics are designed to work optimally with the lutetium orthosilicate (LSO) scintillator. Clinical performance of the LSO PET/CT is examined before and after upgrading to the new PICO 3D electronics, and compared with results using the NEMA NU 2 standard for evaluating scanner performance. Improved noise-equivalent count rates are seen in clinical studies, and reduced scatter fractions are observed, consistent with the increased lower-level energy threshold used to reject scatter events in the upgraded configuration.

  15. SPIRAL CONTACTOR FOR SOLVENT EXTRACTION COLUMN

    DOEpatents

    Cooley, C.R.

    1961-06-13

    The patented extraction apparatus includes a column, perforated plates extending across the column, liquid pulse means connected to the column, and an imperforate spiral ribbon along the length of the column.

  16. Spiral waves on a contractile tissue

    NASA Astrophysics Data System (ADS)

    Mesin, L.; Ambrosi, D.

    2011-02-01

    In a healthy cardiac tissue, electric waves propagate in the form of a travelling pulse, from the apex to the base, and activate the contraction of the heart. Defects in the propagation can destabilize travelling fronts and originate possible new periodic solutions, as spiral waves. Spiral waves are quite stable, but the interplay between currents and strain can distort the periodic pattern, provided the coupling is strong enough. In this paper we investigate the stability of spiral waves on a contractile medium in a non-standard framework, in which the electrical potential dictates the active strain (not stress) of the muscle. The role of conducting and contracting fibers is included in the model and periodic boundary conditions are adopted. A correlation analysis allows to evaluate numerically the range of stability of the parameters for the spiral waves, depending on the strain of the contracted fibers and on the magnitude of the stretch activated current.

  17. Spiral core in singly diffusive excitable media

    SciTech Connect

    Kessler, D.A. ); Levine, H.; Reynolds, W.N. )

    1992-01-20

    We formulate the problem of finding the spiral core which smoothly matches onto the asymptotic rotating solution of the FitzHugh-Nagumo model. We prove that the inner problem (with scale {epsilon}, the ratio of the reaction rates) has a solution for all possible outer solutions on scale {epsilon}{sup 2/3}; furthermore, we explicitly determine this solution via a simple numerical procedure. This completes the rigorous demonstration of the existence of rotating spiral solutions in singly diffusive excitable systems.

  18. View factors of cylindrical spiral surfaces

    NASA Astrophysics Data System (ADS)

    Lebedev, Vladimir A.; Solovjov, Vladimir P.

    2016-03-01

    Analytical expressions are presented for the view factors (radiative configuration factors) associated with the flat right cylindrical spiral surface. Such cylindrical spiral systems are widely applied as electrical resistance heating elements for lighting devices, electronic radio tubes, high-speed gas flow heaters, and other appliances used for scientific, industrial and domestic purposes. Derivation of the view factors is based on the invariant principles and the results presented in Lebedev (2000, 2003,1988) [1-3].

  19. Incorporating multislice imaging into x-ray CT polymer gel dosimetry

    SciTech Connect

    Johnston, H.; Hilts, M.; Jirasek, A.

    2015-04-15

    Purpose: To evaluate multislice computed tomography (CT) scanning for fast and reliable readout of radiation therapy (RT) dose distributions using CT polymer gel dosimetry (PGD) and to establish a baseline assessment of image noise and uniformity in an unirradiated gel dosimeter. Methods: A 16-slice CT scanner was used to acquire images through a 1 L cylinder filled with water. Additional images were collected using a single slice machine. The variability in CT number (N{sub CT}) associated with the anode heel effect was evaluated and used to define a new slice-by-slice background subtraction artifact removal technique for CT PGD. Image quality was assessed for the multislice system by evaluating image noise and uniformity. The agreement in N{sub CT} for slices acquired simultaneously using the multislice detector array was also examined. Further study was performed to assess the effects of increasing x-ray tube load on the constancy of measured N{sub CT} and overall scan time. In all cases, results were compared to the single slice machine. Finally, images were collected throughout the volume of an unirradiated gel dosimeter to quantify image noise and uniformity before radiation is delivered. Results: Slice-by-slice background subtraction effectively removes the variability in N{sub CT} observed across images acquired simultaneously using the multislice scanner and is the recommended background subtraction method when using a multislice CT system. Image noise was higher for the multislice system compared to the single slice scanner, but overall image quality was comparable between the two systems. Further study showed N{sub CT} was consistent across image slices acquired simultaneously using the multislice detector array for each detector configuration of the slice thicknesses examined. In addition, the multislice system was found to eliminate variations in N{sub CT} due to increasing x-ray tube load and reduce scanning time by a factor of 4 when compared to

  20. DO BARS DRIVE SPIRAL DENSITY WAVES?

    SciTech Connect

    Buta, Ronald J.; Knapen, Johan H.; Elmegreen, Bruce G.; Salo, Heikki; Laurikainen, Eija; Elmegreen, Debra Meloy; Puerari, Ivanio; Block, David L. E-mail: jhk@iac.es E-mail: hsalo@sun3.oulu.fi E-mail: elmegreen@vassar.edu E-mail: David.Block@wits.ac.za

    2009-05-15

    We present deep near-infrared K{sub s} -band Anglo-Australian Telescope Infrared Imager and Spectrograph observations of a selected sample of nearby barred spiral galaxies, including some with the strongest known bars. The sample covers a range of Hubble types from SB0{sup -} to SBc. The goal is to determine if the torque strengths of the spirals correlate with those of the bars, which might be expected if the bars actually drive the spirals as has been predicted by theoretical studies. This issue has implications for interpreting bar and spiral fractions at high redshift. Analysis of previous samples suggested that such a correlation exists in the near-infrared, where effects of extinction and star formation are less important. However, the earlier samples had only a few excessively strong bars. Our new sample largely confirms our previous studies, but still any correlation is relatively weak. We find two galaxies, NGC 7513 and UGC 10862, where there is only a weak spiral in the presence of a very strong bar. We suggest that some spirals probably are driven by their bars at the same pattern speed, but that this may be only when the bar is growing or if there is abundant gas and dissipation.

  1. SIGNATURES OF LONG-LIVED SPIRAL PATTERNS

    SciTech Connect

    Martinez-Garcia, Eric E.; Gonzalez-Lopezlira, Rosa A. E-mail: martinez@astro.unam.mx

    2013-03-10

    Azimuthal age/color gradients across spiral arms are a signature of long-lived spirals. From a sample of 19 normal (or weakly barred) spirals where we have previously found azimuthal age/color gradient candidates, 13 objects were further selected if a two-armed grand-design pattern survived in a surface density stellar mass map. Mass maps were obtained from optical and near-infrared imaging, by comparison with a Monte Carlo library of stellar population synthesis models that allowed us to obtain the mass-to-light ratio in the J band, (M/L){sub J}, as a function of (g - i) versus (i - J) color. The selected spirals were analyzed with Fourier methods in search of other signatures of long-lived modes related to the gradients, such as the gradient divergence toward corotation, and the behavior of the phase angle of the two-armed spiral in different wavebands, as expected from theory. The results show additional signatures of long-lived spirals in at least 50% of the objects.

  2. Analytical forms of chaotic spiral arms

    NASA Astrophysics Data System (ADS)

    Harsoula, M.; Efthymiopoulos, C.; Contopoulos, G.

    2016-07-01

    We develop an analytical theory of chaotic spiral arms in galaxies. This is based on the Moser theory of invariant manifolds around unstable periodic orbits. We apply this theory to the chaotic spiral arms, which start from the neighbourhood of the Lagrangian points L1 and L2 at the end of the bar in a barred-spiral galaxy. The series representing the invariant manifolds starting at the Lagrangian points L1, L2, or unstable periodic orbits around L1 and L2, yield spiral patterns in the configuration space. These series converge in a domain around every Lagrangian point, called `Moser domain', and represent the orbits that constitute the chaotic spiral arms. In fact, these orbits are not only along the invariant manifolds, but also in a domain surrounding the invariant manifolds. We show further that orbits starting outside the Moser domain but close to it converge to the boundary of the Moser domain, which acts as an attractor. These orbits stay for a long time close to the spiral arms before escaping to infinity.

  3. Instability of spiral convective vortex

    NASA Astrophysics Data System (ADS)

    Evgrafova, Anna; Andrey, Sukhanovsky; Elena, Popova

    2014-05-01

    Formation of large-scale vortices in atmosphere is one of the interesting problems of geophysical fluid dynamics. Tropical cyclones are examples of atmospheric spiral vortices for which convection plays an important role in their formation and evolution. Our study is focused on intensive cyclonic vortex produced by heating in the central part of the rotating layer. The previous studies made by Bogatyrev et al, showed that structure of such vortex is very similar to the structure of tropical cyclones. Qualitative observations described in (Bogatyrev, 2009) showed that the evolution of large-scale vortex in extreme regimes can be very complicated. Our main goal is the study of evolution of convective cyclonic vortex at high values of Grasshof number by PIV system. Experimental setup is a rotating cylindrical tank of fluid (radius 150 mm, depth 30 mm, free upper surface). Velocity fields for different values of heat flux were obtained and temporal and spatial structure of intensive convective vortex were studied in details. With the use of PIV data vorticity fields were reconstructed in different horizontal cross-sections. Physical interpretation of mechanisms that lead to the crucial change in the vortex structure with the growth of heat rate is described. Financial support from program of UD RAS, the International Research Group Program supported by Perm region Government is gratefully acknowledged.

  4. Spiral arms as cosmic ray source distributions

    NASA Astrophysics Data System (ADS)

    Werner, M.; Kissmann, R.; Strong, A. W.; Reimer, O.

    2015-04-01

    The Milky Way is a spiral galaxy with (or without) a bar-like central structure. There is evidence that the distribution of suspected cosmic ray sources, such as supernova remnants, are associated with the spiral arm structure of galaxies. It is yet not clearly understood what effect such a cosmic ray source distribution has on the particle transport in our Galaxy. We investigate and measure how the propagation of Galactic cosmic rays is affected by a cosmic ray source distribution associated with spiral arm structures. We use the PICARD code to perform high-resolution 3D simulations of electrons and protons in galactic propagation scenarios that include four-arm and two-arm logarithmic spiral cosmic ray source distributions with and without a central bar structure as well as the spiral arm configuration of the NE2001 model for the distribution of free electrons in the Milky Way. Results of these simulation are compared to an axisymmetric radial source distribution. Also, effects on the cosmic ray flux and spectra due to different positions of the Earth relative to the spiral structure are studied. We find that high energy electrons are strongly confined to their sources and the obtained spectra largely depend on the Earth's position relative to the spiral arms. Similar finding have been obtained for low energy protons and electrons albeit at smaller magnitude. We find that even fractional contributions of a spiral arm component to the total cosmic ray source distribution influences the spectra on the Earth. This is apparent when compared to an axisymmetric radial source distribution as well as with respect to the Earth's position relative to the spiral arm structure. We demonstrate that the presence of a Galactic bar manifests itself as an overall excess of low energy electrons at the Earth. Using a spiral arm geometry as a cosmic ray source distributions offers a genuine new quality of modeling and is used to explain features in cosmic ray spectra at the Earth

  5. Stellar Orbital Studies in Normal Spiral Galaxies: Effect of Spiral Arms on Disk Dynamics

    NASA Astrophysics Data System (ADS)

    Pérez-Villegas, A.; Pichardo, B.; Moreno, E.

    2015-10-01

    We have built a family of non-axisymmetric potential models for normal non-barred spiral galaxies. For this purpose, a three-dimensional self-gravitating model of spiral arms (PERLAS) is used. We analyze the stellar dynamics on the disk plane, varying structural and dynamical parameters such as pitch angle, strength of spiral arms and angular speed. For the pitch angle, we found two limits. The first limit, based on ordered behavior, periodic orbit studies show that for pitch angles up to approximately 15{(°) }, 18{(°) }, and 20{(°) } for Sa, Sb and Sc galaxies, respectively, the spiral arms could be long-lasting structures. Beyond those limits, spiral arms may be explained as transient features rather than long-lasting large-scale structures. In a second limit, from a phase space orbital study based on chaotic behavior, we found that for pitch angles larger than ˜ 30{(°) }, ˜ 40{(°) } and ˜ 50{(°) } for Sa, Sb, and Sc galaxies, respectively, chaotic orbits dominate all the prograde phase space region that surrounds the periodic orbits sculpting the spiral arms, and can even destroy them. Finally, we studied orbital dynamics varying other parameters such as the pattern speed and the spiral arm mass; also we looked for restrictions for these parameters in different morphological types. In these studies we noticed that the effect of spiral arms on the disk dynamics, when we vary the pattern speed and mass, is strongly linked to the pitch angle.

  6. Spiral hyperlens with enhancements of image resolution and magnification

    NASA Astrophysics Data System (ADS)

    Chen, Yi-An; Chang, I.-Ling; Chen, Lien-Wen

    2016-06-01

    A subwavelength spiral hyperlens that is able to image beyond the diffraction limit is studied. The spiral hyperlens is made from an anisotropic metamaterial with a hyperbolic dispersion relation in which the evanescent wave is converted into a propagating wave. Therefore, the propagating wave can be processed by conventional optical systems outside of the spiral hyperlens. The possibility of using a cylindrical hyperlens for overcoming the diffraction limit has been proven analytically and experimentally. In this study, we designed two types of spiral hyperlenses composed of a spiral periodic stack of silver and alumina multilayers. A spiral hyperlens utilizes the spiral geometry to magnify the objects. In comparison with a cylindrical hyperlens, a spiral hyperlens has improved performance in terms of higher image resolution and better image magnifications. Numerical simulations illustrate that the far-field imaging resolution of cylindrical spiral hyperlens is no greater than 110 nm at 365 nm working wavelength.

  7. Molecular gas in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Casoli, F.; Sauty, S.; Gerin, M.; Boselli, A.; Fouque, P.; Braine, J.; Gavazzi, G.; Lequeux, J.; Dickey, J.

    1998-03-01

    The molecular hydrogen content of a galaxy is a key parameter for its activity and future evolution. Its variations with basic properties such as size, mass, morphological type, and environment, the ratio of molecular to atomic gas masses, should provide us with a better view of galaxy evolution. Such studies have been done in the past by Sage (1993a) or the FCRAO group (e.g. Young & Knezek 1989), and have led to controversial results, for example about the MHH /MHI ratio. While Sage (1993a), using a distance-limited sample of 65 galaxies and the \\COA line emission as a tracer of the HH mass, finds that most galaxies have MHH /MHI lower than 1, Young & Knezek (1989) and Young et al. (1995), from a different sample of 178 objects, claim equal amounts of gas in the molecular and atomic phase. Here we again tackle this problem, by gathering a much larger sample of 582 objects, not only from the literature but also from several \\COA surveys that we have completed and which are largely unpublished. Our sample is clearly not complete and contains a large number of cluster galaxies as well as many more massive objects than a distance-limited sample. Contrary to previous analyses, we have taken into account the non-detections by using the survival analysis method. Our sample includes 105 isolated galaxies, observed by us, that we use as a reference sample in order to determine whether cluster galaxies are CO-deficient. We find that the ratio of HH and HI masses is on the average lower than 1, with = log(0.20) +/- 0.04 (median = log(0.27) +/- 0.04). For spirals with types Sa to Sc, we have slightly higher values: log(0.28) and log(0.34) respectively. The actual HH masses and MHH /MHI ratios could be lower than given above if, as suggested by recent gamma -ray and 1.3 mm continuum data, the conversion factor between \\COA emissivities and HH masses for large spiral galaxies is lower than the value adopted here (X=2.310(20) cm(-2) /(Kkms(-1) )). The

  8. Spiral Development for Safeguards Instrumentation

    SciTech Connect

    Koskelo, M.; Undem, Halvor A.; Good, Morris S.; Frazar, Sarah L.; Schanfein, Mark; Kadner, S.

    2012-10-12

    Safeguards instrumentation is highly specialized, so a common approach in the US has been to develop initial prototypes for performance, operability and security within the US National Laboratories for the IAEA and then seek one or more commercial partners. Transfer of technology from US National Laboratories is a legal requirement for products that have the potential for mass production. Other important objectives include minimizing time to deployment and lifecycle cost, and optimizing product maintainability, sustainability and manufacturability. Unfortunately, the deployment of systems developed via this model has sometimes been seriously delayed or never adopted because of the difficulty of optimizing the significant parameters of the process between the public and private sectors. The authors suggest that forming an R&D partnership between a research laboratory and a commercial company much earlier in the process would provide significant advantages. The present US practice leads to unnecessary expenditures during the early R&D phase since many decisions are made based on research needs that are counterproductive for commercialization and manufacturability. If the ultimate goal of the project is to produce a reliable and cost effective commercial product, the commercial input is needed early and often. The new “model” of developing systems in a closer collaboration with the private sector, in a spiral “Commercialization by Design” approach, should also limit the long term financial mortgages that Member States frequently experience with respect to safeguards instrumentation development using the present process. As a concrete example, the potential for incorporating Wire Integrity Verification Technology into the iCobra Reader System is discussed.

  9. The molecular spiral arms of NGC 6946

    NASA Technical Reports Server (NTRS)

    Tacconi, L. J.; Xie, S.

    1990-01-01

    From CO-12(J=1 to 0) observations at 45 seconds resolution Tacconi and Young (1989) have found evidence for enhancements in both the CO emissivity and the massive star formation efficiency (MSFE) on optical spiral arms of the bright spiral galaxy NGC 6946. In the optically luminous and well-defined spiral arm in the NE quadrant, there are enhancements in both the H2 surface density and MSFE relative to the interarm regions. In contrast, a poorly defined arm in the SW shows no arm-interarm contrast in the MSFE. To further investigate the molecular gas content of these two spiral arms, researchers have made CO-12 J=2 to 1 and 3 to 2 observations with the James Clerk Maxwell Telescope. In the J=2 to 1 line, they made observations of the NE and SW spiral arm and interarm regions in 4 x 9 10 seconds spaced grids (36 points per grid). Because of decreased sensitivity in the J=3 to 2 line, they were limited to mapping the two arm regions in 2 x 3 10 seconds spaced grids (6 points per grid). The centers of each of the grids lie 2.4 minutes to the NE and 2.3 minutes to the SW of the nucleus of NGC 6946. With the CO J=2 to 1 data researchers are able to fully resolve the two observed spiral arms in NGC 6946. In both cases the CO emission is largely confined to the optical spiral arm regions with the peak observed T asterisk sub A being up to 4 times higher on the spiral arms than in the interarm regions. Researchers are currently estimating massive star formation efficiencies on and off the spiral arms through direct comparison of the CO maps with an H alpha image. They are also comparing the CO J=2 to 1 data with an HI map made at similar resolution. Thus, they will be able to determine structure in all components of the IS on scales of less than 20 inches.

  10. Long-lived spiral waves in N-body simulations

    NASA Technical Reports Server (NTRS)

    Comins, Neil F.; Schroeder, Michael C.

    1989-01-01

    Results of N-body simulations of disc galaxies using a two-dimensional Cartesian N-body code are presented. Both trailing arm spirals (TAS) and leading arm spirals (LAS) were used with varieties of pitch angles and pattern speeds. LAS perturbations transferred their energy to TAS via swing amplification; TAS perturbations led to TAS arms. In both cases the spiral arms persisted for more than 5 rotation periods, but the maximum amplitude 2-armed spirals were generated by LAS perturbations. The persistence of the trailing arm spiral waves is thought to be caused by the kinematic spiral arm mechanism described by Kalnajs (1973).

  11. Serial CT features of pulmonary leptospirosis in 10 dogs.

    PubMed

    Gendron, K; Christe, A; Walter, S; Schweighauser, A; Francey, T; Doherr, M G; Lang, J

    2014-02-15

    Leptospirosis pulmonary haemorrhage syndrome (LPHS) is a frequent manifestation of Leptospira infection in dogs and is associated with a high morbidity and mortality. Three helical 16-slice thoracic CT scans were performed in 10 dogs naturally infected with Leptospira, within 24 hours of admission, and three and seven days later. Patients were sedated and scanned without breathhold, with a protocol adapted for rapid scanning. One dog died of respiratory failure on the morning following the first scan. On the initial scan, imaging features of LPHS included ground-glass nodules (10/10), peribronchovascular interstitial thickening (10/10), diffuse or patchy ground-glass opacity (9/10), solid nodules (8/10) and consolidation (7/10). Temporary bronchiolar dilation was observed in all dogs in association with peribronchovascular interstitial thickening, which had completely resolved at day 7. Nodules were with few exceptions assigned to the centrilobular region. Regression of lesion severity was observed after each subsequent scan. Consolidation and solid nodules changed over time into lesions of ground-glass attenuation. Pleural effusion (3/10) and mediastinal effusion (2/10) were mild and transient. Lesion severity appeared unassociated with survival to discharge. PMID:24420873

  12. The Spiral Curriculum: implications for online learning

    PubMed Central

    Masters, Kenneth; Gibbs, Trevor

    2007-01-01

    Background There is an apparent disjuncture between the requirements of the medical spiral curriculum and the practice of replacing previous online material in undergraduate courses. This paper investigates the extent to which students revisit previous online material for the purposes of building the educational spiral, and the implications for the implementation of a Faculty's Learning Management System implementation. Methods At the University of Cape Town, medical students' last date of access to 16 previous online courses was determined. Students completed a survey to determine their reasons for revisiting this material and the perceived benefits of this availability. Results 70% of the students revisited their previous online courses. The major reasons were to review lecture presentations, lectures notes, and quizzes. The perceived benefits were for understanding new material, preparation for assessments, and convenience. Although student comments were not always in line with the concept of the spiral curriculum, most referred to processes of building on previous work, and some mentioned the spiral curriculum specifically. Conclusion This study suggests that the practice of replacing previous online courses may hinder rather than support student learning. Although students visit previous material for ranges of reasons, a large number are aware of the spiral curriculum, and use the online environment to build upon previous material. Any practice, which entails replacing material and redesigning curricula content may be detrimental to the students' future learning needs, and such activities may need revision. PMID:18154654

  13. Spiral: Automated Computing for Linear Transforms

    NASA Astrophysics Data System (ADS)

    Püschel, Markus

    2010-09-01

    Writing fast software has become extraordinarily difficult. For optimal performance, programs and their underlying algorithms have to be adapted to take full advantage of the platform's parallelism, memory hierarchy, and available instruction set. To make things worse, the best implementations are often platform-dependent and platforms are constantly evolving, which quickly renders libraries obsolete. We present Spiral, a domain-specific program generation system for important functionality used in signal processing and communication including linear transforms, filters, and other functions. Spiral completely replaces the human programmer. For a desired function, Spiral generates alternative algorithms, optimizes them, compiles them into programs, and intelligently searches for the best match to the computing platform. The main idea behind Spiral is a mathematical, declarative, domain-specific framework to represent algorithms and the use of rewriting systems to generate and optimize algorithms at a high level of abstraction. Experimental results show that the code generated by Spiral competes with, and sometimes outperforms, the best available human-written code.

  14. Circularly symmetric light scattering from nanoplasmonic spirals.

    PubMed

    Trevino, Jacob; Cao, Hui; Dal Negro, Luca

    2011-05-11

    In this paper, we combine experimental dark-field imaging, scattering, and fluorescence spectroscopy with rigorous electrodynamics calculations in order to investigate light scattering from planar arrays of Au nanoparticles arranged in aperiodic spirals with diffuse, circularly symmetric Fourier space. In particular, by studying the three main types of Vogel's spirals fabricated by electron-beam lithography on quartz substrates, we demonstrate polarization-insensitive planar light diffraction in the visible spectral range. Moreover, by combining dark-field imaging with analytical multiparticle calculations in the framework of the generalized Mie theory, we show that plasmonic spirals support distinctive structural resonances with circular symmetry carrying orbital angular momentum. The engineering of light scattering phenomena in deterministic structures with circular Fourier space provides a novel strategy for the realization of optical devices that fully leverage on enhanced, polarization-insensitive light-matter coupling over planar surfaces, such as thin-film plasmonic solar cells, plasmonic polarization devices, and optical biosensors. PMID:21466155

  15. Intertwined Multiple Spiral Fracture in Perforated Sheets

    NASA Astrophysics Data System (ADS)

    Fuentealba, Juan-Francisco; Hamm, Eugenio; Roman, Benoît

    2016-04-01

    We study multiple tearing of a thin, elastic, brittle sheet indented with a rigid cone. The n cracks initially prepared symmetrically propagate radially for n ≥4 . However, if n <4 the radial symmetry is broken and fractures spontaneously intertwine along logarithmic spiral paths, respecting order n rotational symmetry. In the limit of very thin sheets, we find that fracture mechanics is reduced to a geometrical model that correctly predicts the maximum number of spirals to be strictly 4, together with their growth rate and the perforation force. Similar spirals are also observed in a different tearing experiment (this time up to n =4 , in agreement with the model), in which bending energy of the sheet is dominant.

  16. Molecular clouds and galactic spiral structure

    NASA Technical Reports Server (NTRS)

    Dame, T. M.

    1984-01-01

    Galactic CO line emission at 115 GHz was surveyed in order to study the distribution of molecular clouds in the inner galaxy. Comparison of this survey with similar H1 data reveals a detailed correlation with the most intense 21 cm features. To each of the classical 21 cm H1 spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is devised for the galactic distribution of molecular clouds. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide.

  17. Intertwined Multiple Spiral Fracture in Perforated Sheets.

    PubMed

    Fuentealba, Juan-Francisco; Hamm, Eugenio; Roman, Benoît

    2016-04-22

    We study multiple tearing of a thin, elastic, brittle sheet indented with a rigid cone. The n cracks initially prepared symmetrically propagate radially for n≥4. However, if n<4 the radial symmetry is broken and fractures spontaneously intertwine along logarithmic spiral paths, respecting order n rotational symmetry. In the limit of very thin sheets, we find that fracture mechanics is reduced to a geometrical model that correctly predicts the maximum number of spirals to be strictly 4, together with their growth rate and the perforation force. Similar spirals are also observed in a different tearing experiment (this time up to n=4, in agreement with the model), in which bending energy of the sheet is dominant. PMID:27152809

  18. Smoothing Rotation Curves in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Berrier, Joel C.; Sellwood, Jerry

    2014-05-01

    We present evidence that spiral activity is responsible for the creation of featureless rotation curves. We examine a variety of simulations of disk galaxies beginning in equilibrium and allow them to evolve while adding particles in annuli to the hot disk using a variety of rules. Two unstable spiral modes develop when this new material forms a ridge-like feature in the surface density profile of the disk. The extra material is redistributed radially by the spiral activity, and the associated angular momentum changes remove more particles from the ridge than are added to it. This process eventually removes the density feature from the galaxy and creates a locally flat rotation curve. We argue that the lack of a feature when transitioning from disk to halo dominance in the rotation curves of disk galaxies, the so called ``disk-halo conspiracy'', could also be accounted for by this mechanism.

  19. HOW DIFFERENT ARE NORMAL AND BARRED SPIRALS?

    SciTech Connect

    Van den Bergh, Sidney

    2011-06-15

    No significant color differences are found between normal and barred spirals over the range of Hubble stages a-ab-b-bc. Furthermore, no significant difference is seen between the luminosity distributions of normal and barred galaxies over the same range of Hubble stages. However, SBc galaxies are found to be systematically fainter than Sc galaxies at 99% confidence. The observation that normal and barred spirals with Hubble stages a-ab-b-bc have indistinguishable intrinsic colors hints at the possibility that the bars in such spiral galaxies might be ephemeral structures. Finally, it is pointed out that lenticular galaxies of types S0 and SB0 are systematically fainter than are other early-type galaxies, suggesting that such galaxies are situated on evolutionary tracks that differ systematically from those of galaxies that lie along the E-Sa-Sb-Sc and E-SBa-SBb-SBc sequences.

  20. Discontinuous Spirals of Stable Periodic Oscillations

    PubMed Central

    Sack, Achim; Freire, Joana G.; Lindberg, Erik; Pöschel, Thorsten; Gallas, Jason A. C.

    2013-01-01

    We report the experimental discovery of a remarkable organization of the set of self-generated periodic oscillations in the parameter space of a nonlinear electronic circuit. When control parameters are suitably tuned, the wave pattern complexity of the periodic oscillations is found to increase orderly without bound. Such complex patterns emerge forming self-similar discontinuous phases that combine in an artful way to produce large discontinuous spirals of stability. This unanticipated discrete accumulation of stability phases was detected experimentally and numerically in a Duffing-like proxy specially designed to bypass noisy spectra conspicuously present in driven oscillators. Discontinuous spirals organize the dynamics over extended parameter intervals around a focal point. They are useful to optimize locking into desired oscillatory modes and to control complex systems. The organization of oscillations into discontinuous spirals is expected to be generic for a class of nonlinear oscillators. PMID:24284508

  1. Cinematique et dynamique des galaxies spirales barrees

    NASA Astrophysics Data System (ADS)

    Hernandez, Olivier

    The total mass (luminous and dark) of galaxies is derived from their circular velocities. Spectroscopic Fabry-Perot observations of the ionized gas component of spiral galaxies allow one to derive their kinematics. In the case of purely axisymmetric velocity fields--as in non-active and unbarred spirals galaxies-- the circular velocities can be derived directly. However, the velocity fields of barred galaxies (which constitute two thirds of the spirals) exhibit strong non-circular motions and need a careful analysis to retrieve the circular component. This thesis proposes the necessary steps to recover the axisymmetric component of barred spiral galaxies. The first step was to develop the best instrumentation possible for this work. [Special characters omitted.] , which is the most sensitive photon counting camera ever developed, was coupled to a Fabry-Perot interferometer. The observations of a sample of barred spiral galaxies--the BH a BAR sample--was assembled in order to obtain the most rigourous velocity fields. Then, the Tremaine-Weinberg method, which can determine the bar pattern speed and is usually used with the observations of stellar component, has been tested on the ionised gas and gave satisfactory results. Finally, all the above techniques have been applied to the BH a BAR sample in order to study the key parameters of the galaxies' evolution--bar pattern speeds, multiple stationary waves, resonances etc.--which will allow one to use N-body+SPH simulations to model properly the non-circular motions and determine the true total mass of barred spiral galaxies.

  2. Exploring spiral galaxy potentials with hydrodynamical simulations

    NASA Astrophysics Data System (ADS)

    Slyz, Adrianne D.; Kranz, Thilo; Rix, Hans-Walter

    2003-12-01

    We study how well the complex gas velocity fields induced by massive spiral arms are modelled by the hydrodynamical simulations that we used recently to constrain the dark matter fraction in nearby spiral galaxies. More specifically, we explore the dependence of the positions and amplitudes of features in the gas flow on the temperature of the interstellar medium (assumed to behave as a one-component isothermal fluid), the non-axisymmetric disc contribution to the galactic potential, the pattern speed Ωp, and finally the numerical resolution of the simulation. We argue that, after constraining the pattern speed reasonably well by matching the simulations to the observed spiral arm morphology, the amplitude of the non-axisymmetric perturbation (the disc fraction) is left as the primary parameter determining the gas dynamics. However, owing to the sensitivity of the positions of the shocks to modelling parameters, one has to be cautious when quantitatively comparing the simulations to observations. In particular, we show that a global least-squares analysis is not the optimal method for distinguishing different models, as it tends to slightly favour low disc fraction models. Nevertheless, we conclude that, given observational data of reasonably high spatial resolution and an accurate shock-resolving hydro-code, this method tightly constrains the dark matter content within spiral galaxies. We further argue that, even if the perturbations induced by spiral arms are weaker than those of strong bars, they are better suited for this kind of analysis because the spiral arms extend to larger radii where effects like inflows due to numerical viscosity and morphological dependence on gas sound speed are less of a concern than they are in the centres of discs.

  3. Spiral computed tomography of fetuses: reference data and interest in fetopathy

    NASA Astrophysics Data System (ADS)

    Braillon, Pierre M.; Bouvier, Raymonde

    1999-09-01

    The aim of this work was to define reference values for the skeletal and total body volumes (SV and TBV) of human fetuses from 3D reconstructions obtained with spiral computed tomography (CT). The interest of the technique in fetopathy was also estimated. Twenty three fetuses who died just before delivery were studied. The causes of death were not associated with any metabolism abnormality, and all these babies were appropriated for gestational age (GA: 14 - 41.5 wks; Body Weight BW: 22 - 3760 g). They were scanned with a spiral mode on a CT scanner (Elscint CT Twin) using a 2.7 mm slice thickness, a pitch value of 0.7, and a 512 X 512 image matrix. Lengths and volumes were measured on 3D images reconstructed with appropriate windows. High correlations (r greater than 0.95) were found between BW, SV or TBV and the long bone lengths. The ratio SV/TBV was 8.2 plus or minus 0.2%. With the scanning and analysis parameters used, it was extremely difficult to make a precise segmentation of a given organ. However, some few alterations of these parameters could largely increase the potential of the technique in fetopathy.

  4. SU-E-T-541: Measurement of CT Density Model Variations and the Impact On the Accuracy of Monte Carlo (MC) Dose Calculation in Stereotactic Body Radiation Therapy for Lung Cancer

    SciTech Connect

    Xiang, H; Li, B; Behrman, R; Russo, G; Kachnic, L; Lu, H; Fernando, H

    2015-06-15

    Purpose: To measure the CT density model variations between different CT scanners used for treatment planning and impact on the accuracy of MC dose calculation in lung SBRT. Methods: A Gammex electron density phantom (RMI 465) was scanned on two 64-slice CT scanners (GE LightSpeed VCT64) and a 16-slice CT (Philips Brilliance Big Bore CT). All three scanners had been used to acquire CT for CyberKnife lung SBRT treatment planning. To minimize the influences of beam hardening and scatter for improving reproducibility, three scans were acquired with the phantom rotated 120° between scans. The mean CT HU of each density insert, averaged over the three scans, was used to build the CT density models. For 14 patient plans, repeat MC dose calculations were performed by using the scanner-specific CT density models and compared to a baseline CT density model in the base plans. All dose re-calculations were done using the same plan beam configurations and MUs. Comparisons of dosimetric parameters included PTV volume covered by prescription dose, mean PTV dose, V5 and V20 for lungs, and the maximum dose to the closest critical organ. Results: Up to 50.7 HU variations in CT density models were observed over the baseline CT density model. For 14 patient plans examined, maximum differences in MC dose re-calculations were less than 2% in 71.4% of the cases, less than 5% in 85.7% of the cases, and 5–10% for 14.3% of the cases. As all the base plans well exceeded the clinical objectives of target coverage and OAR sparing, none of the observed differences led to clinically significant concerns. Conclusion: Marked variations of CT density models were observed for three different CT scanners. Though the differences can cause up to 5–10% differences in MC dose calculations, it was found that they caused no clinically significant concerns.

  5. Ultraviolet Spectra of Normal Spiral Galaxies

    NASA Technical Reports Server (NTRS)

    Kinney, Anne

    1997-01-01

    The data related to this grant on the Ultraviolet Spectra of Normal Spiral Galaxies have been entirely reduced and analyzed. It is incorporated into templates of Spiral galaxies used in the calculation of K corrections towards the understanding of high redshift galaxies. The main paper was published in the Astrophysical Journal, August 1996, Volume 467, page 38. The data was also used in another publication, The Spectral Energy Distribution of Normal Starburst and Active Galaxies, June 1997, preprint series No. 1158. Copies of both have been attached.

  6. Spiral computed tomography with two- and three-dimensional reconstruction in the management of tibial plateau fractures.

    PubMed

    Liow, R Y; Birdsall, P D; Mucci, B; Greiss, M E

    1999-10-01

    Spiral computed tomography (CT) with three-dimensional and multiplanar reconstructions was used in the evaluation of tibial fractures in nine patients. Computed tomography added important information to that obtained by plain radiographs. Five (55%) fractures were reclassified. The degree of articular depression was often underappreciated on plain radiographs. Furthermore, the fracture complexity and the spatial relation of fragments could be readily demonstrated with 3-D reconstruction. This technique is useful in planning operative reconstruction. PMID:10535555

  7. Cochlear anatomy using micro computed tomography (μCT) imaging

    NASA Astrophysics Data System (ADS)

    Kim, Namkeun; Yoon, Yongjin; Steele, Charles; Puria, Sunil

    2008-02-01

    A novel micro computed tomography (μCT) image processing method was implemented to measure anatomical features of the gerbil and chinchilla cochleas, taking into account the bent modailosis axis. Measurements were made of the scala vestibule (SV) area, the scala tympani (SV) area, and the basilar membrane (BM) width using prepared cadaveric temporal bones. 3-D cochlear structures were obtained from the scanned images using a process described in this study. It was necessary to consider the sharp curvature of mododailosis axis near the basal region. The SV and ST areas were calculated from the μCT reconstructions and compared with existing data obtained by Magnetic Resonance Microscopy (MRM), showing both qualitative and quantitative agreement. In addition to this, the width of the BM, which is the distance between the primary and secondary osseous spiral laminae, is calculated for the two animals and compared with previous data from the MRM method. For the gerbil cochlea, which does not have much cartilage in the osseous spiral lamina, the μCT-based BM width measurements show good agreement with previous data. The chinchilla BM, which contains more cartilage in the osseous spiral lamina than the gerbil, shows a large difference in the BM widths between the μCT and MRM methods. The SV area, ST area, and BM width measurements from this study can be used in building an anatomically based mathematical cochlear model.

  8. Principles of CT and CT technology.

    PubMed

    Goldman, Lee W

    2007-09-01

    This article provides a review of the basic principles of CT within the context of the evolution of CT. Modern CT technology can be understood as a natural progression of improvements and innovations in response to both engineering problems and clinical requirements. Detailed discussions of multislice CT, CT image quality evaluation, and radiation doses in CT will be presented in upcoming articles in this series. PMID:17823453

  9. Lumbosacral spine CT

    MedlinePlus

    Spinal CT; CT - lumbosacral spine ... In other cases, a CT of the lumbosacral spine may be done after injecting contrast dye into ... of the body. A CT of the lumbosacral spine can evaluate fractures and changes of the spine, ...

  10. 2DFFT: Measuring Galactic Spiral Arm Pitch Angle

    NASA Astrophysics Data System (ADS)

    Davis, Benjamin L.; Berrier, Joel C.; Shields, Douglas W.; Kennefick, Julia; Kennefick, Daniel; Seigar, Marc S.; Lacy, Claud H. S.; Puerari, Ivânio

    2016-08-01

    2DFFT utilizes two-dimensional fast Fourier transformations of images of spiral galaxies to isolate and measure the pitch angles of their spiral arms; this provides a quantitative way to measure this morphological feature and allows comparison of spiral galaxy pitch angle to other galactic parameters and test spiral arm genesis theories. 2DFFT requires fourn.c from Numerical Recipes in C (Press et al. 1989).

  11. Differential diagnosis of solitary pulmonary nodules with dual-source spiral computed tomography

    PubMed Central

    Shi, Zhitao; Wang, Yanhui; He, Xueqi

    2016-01-01

    The aim of the present study was to analyze the value of applying dual-source 64-layer spiral computed tomography (CT) in the differential diagnosis of solitary pulmonary nodules (SPNs). Mediastinal windows from 45 cases were selected to study SPNs (maximum diameter, ≤3 cm), and the pathological nature of lesions was determined by clinical and pathological diagnosis. Conventional 64-layer spiral CT scanning, local enhancement and 3D recombination technologies were used to determine the occurrence rate, lesion diameter, degree of enhancement, lobular sign, spicule sign, pleural indentation sign, vessel convergence sign and bronchus sign. The final diagnoses indicated 34 cases of malignant SPNs (75.6%) and 11 benign cases (24.4%). When the nodule diameter in the malignant group was compared with that of the benign group, the difference was not statistically significant (P>0.05). Nodules in the malignant group showed inhomogeneous enhancement while nodules in the benign group showed homogeneous enhancement. The enhanced CT values in the malignant group were higher than those in the benign group, and the difference was statistically significant (P<0.05). The proportion of nodules with lobular sign in the malignant group was significantly higher than that in the benign group (P<0.05). The proportion of nodules with calcification, vessel convergence sign and bronchus sign in the malignant group were significantly higher than those in the benign group, and the differences were statistically significant (P<0.05). A comparison of vacuole sign, pleural indentation sign, spiculate protuberance and fat occurrence between the two groups yielded no statistically significant differences (P>0.05). The sensitivity of CT enhancement was 85.6%, specificity was 79.6%, positive predicated value was 92.3%, and the negative predicted value was 85.2%. In conclusion, SPNs diagnosed by CT enhancement manifested with enhancement degree, lobular sign, calcification, vessel convergence sign

  12. Thoracic CT

    MedlinePlus

    ... table that slides into the center of the scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. ... than 300 pounds, have your doctor contact the scanner operator before the exam. CT scanners have a ...

  13. Computer numerical control grinding of spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Scott, H. Wayne

    1991-01-01

    The development of Computer Numerical Control (CNC) spiral bevel gear grinding has paved the way for major improvement in the production of precision spiral bevel gears. The object of the program was to decrease the setup, maintenance of setup, and pattern development time by 50 percent of the time required on conventional spiral bevel gear grinders. Details of the process are explained.

  14. Sinogram restoration for ultra-low-dose x-ray multi-slice helical CT by nonparametric regression

    NASA Astrophysics Data System (ADS)

    Jiang, Lu; Siddiqui, Khan; Zhu, Bin; Tao, Yang; Siegel, Eliot

    2007-03-01

    During the last decade, x-ray computed tomography (CT) has been applied to screen large asymptomatic smoking and nonsmoking populations for early lung cancer detection. Because a larger population will be involved in such screening exams, more and more attention has been paid to studying low-dose, even ultra-low-dose x-ray CT. However, reducing CT radiation exposure will increase noise level in the sinogram, thereby degrading the quality of reconstructed CT images as well as causing more streak artifacts near the apices of the lung. Thus, how to reduce the noise levels and streak artifacts in the low-dose CT images is becoming a meaningful topic. Since multi-slice helical CT has replaced conventional stop-and-shoot CT in many clinical applications, this research mainly focused on the noise reduction issue in multi-slice helical CT. The experiment data were provided by Siemens SOMATOM Sensation 16-Slice helical CT. It included both conventional CT data acquired under 120 kvp voltage and 119 mA current and ultra-low-dose CT data acquired under 120 kvp and 10 mA protocols. All other settings are the same as that of conventional CT. In this paper, a nonparametric smoothing method with thin plate smoothing splines and the roughness penalty was proposed to restore the ultra-low-dose CT raw data. Each projection frame was firstly divided into blocks, and then the 2D data in each block was fitted to a thin-plate smoothing splines' surface via minimizing a roughness-penalized least squares objective function. By doing so, the noise in each ultra-low-dose CT projection was reduced by leveraging the information contained not only within each individual projection profile, but also among nearby profiles. Finally the restored ultra-low-dose projection data were fed into standard filtered back projection (FBP) algorithm to reconstruct CT images. The rebuilt results as well as the comparison between proposed approach and traditional method were given in the results and

  15. Investigation of Spiral and Sweeping Holes

    NASA Technical Reports Server (NTRS)

    Thurman, Douglas; Poinsatte, Philip; Ameri, Ali; Culley, Dennis; Raghu, Surya; Shyam, Vikram

    2015-01-01

    Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing rations of 1.0, 1.5, 2.0, and 2.5 at a density ration of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.

  16. Maximum life spiral bevel reduction design

    NASA Technical Reports Server (NTRS)

    Savage, M.; Prasanna, M. G.; Coe, H. H.

    1992-01-01

    Optimization is applied to the design of a spiral bevel gear reduction for maximum life at a given size. A modified feasible directions search algorithm permits a wide variety of inequality constraints and exact design requirements to be met with low sensitivity to initial values. Gear tooth bending strength and minimum contact ratio under load are included in the active constraints. The optimal design of the spiral bevel gear reduction includes the selection of bearing and shaft proportions in addition to gear mesh parameters. System life is maximized subject to a fixed back-cone distance of the spiral bevel gear set for a specified speed ratio, shaft angle, input torque, and power. Significant parameters in the design are: the spiral angle, the pressure angle, the numbers of teeth on the pinion and gear, and the location and size of the four support bearings. Interpolated polynomials expand the discrete bearing properties and proportions into continuous variables for gradient optimization. After finding the continuous optimum, a designer can analyze near optimal designs for comparison and selection. Design examples show the influence of the bearing lives on the gear parameters in the optimal configurations. For a fixed back-cone distance, optimal designs with larger shaft angles have larger service lives.

  17. STRUCTURED MOLECULAR GAS REVEALS GALACTIC SPIRAL ARMS

    SciTech Connect

    Sawada, Tsuyoshi; Hasegawa, Tetsuo; Koda, Jin

    2012-11-01

    We explore the development of structures in molecular gas in the Milky Way by applying the analysis of the brightness distribution function and the brightness distribution index (BDI) in the archival data from the Boston University-Five College Radio Astronomy Observatory {sup 13}CO J = 1-0 Galactic Ring Survey. The BDI measures the fractional contribution of spatially confined bright molecular emission over faint emission extended over large areas. This relative quantity is largely independent of the amount of molecular gas and of any conventional, pre-conceived structures, such as cores, clumps, or giant molecular clouds. The structured molecular gas traced by higher BDI is located continuously along the spiral arms in the Milky Way in the longitude-velocity diagram. This clearly indicates that molecular gas changes its structure as it flows through the spiral arms. Although the high-BDI gas generally coincides with H II regions, there is also some high-BDI gas with no/little signature of ongoing star formation. These results support a possible evolutionary sequence in which unstructured, diffuse gas transforms itself into a structured state on encountering the spiral arms, followed by star formation and an eventual return to the unstructured state after the spiral arm passage.

  18. Spiraling multivortex solitons in nonlocal nonlinear media.

    PubMed

    Buccoliero, Daniel; Desyatnikov, Anton S; Krolikowski, Wieslaw; Kivshar, Yuri S

    2008-01-15

    We demonstrate the existence of a broad class of higher-order rotating spatial solitons in nonlocal nonlinear media. We employ the generalized Hermite-Laguerre-Gaussian ansatz for constructing multivortex soliton solutions and study numerically their dynamics and stability. We discuss in detail the tripole soliton carrying two spiraling phase dislocations, or self-trapped optical vortices. PMID:18197238

  19. Spiral Growth in Plants: Models and Simulations

    ERIC Educational Resources Information Center

    Allen, Bradford D.

    2004-01-01

    The analysis and simulation of spiral growth in plants integrates algebra and trigonometry in a botanical setting. When the ideas presented here are used in a mathematics classroom/computer lab, students can better understand how basic assumptions about plant growth lead to the golden ratio and how the use of circular functions leads to accurate…

  20. Spiral groove seal. [for hydraulic rotating shaft

    NASA Technical Reports Server (NTRS)

    Ludwig, L. P. (Inventor)

    1973-01-01

    Mating flat surfaces inhibit leakage of a fluid around a stationary shaft. A spiral groove pattern produces a pumping action toward the fluid when the shaft rotates which prevents leakage while a generated hydraulic lifting force separates the mating surfaces to minimize wear.

  1. Asymptotic dynamics of reflecting spiral waves.

    PubMed

    Langham, Jacob; Biktasheva, Irina; Barkley, Dwight

    2014-12-01

    Resonantly forced spiral waves in excitable media drift in straight-line paths, their rotation centers behaving as pointlike objects moving along trajectories with a constant velocity. Interaction with medium boundaries alters this velocity and may often result in a reflection of the drift trajectory. Such reflections have diverse characteristics and are known to be highly nonspecular in general. In this context we apply the theory of response functions, which via numerically computable integrals, reduces the reaction-diffusion equations governing the whole excitable medium to the dynamics of just the rotation center and rotation phase of a spiral wave. Spiral reflection trajectories are computed by this method for both small- and large-core spiral waves in the Barkley model. Such calculations provide insight into the process of reflection as well as explanations for differences in trajectories across parameters, including the effects of incidence angle and forcing amplitude. Qualitative aspects of these results are preserved far beyond the asymptotic limit of weak boundary effects and slow resonant drift. PMID:25615159

  2. Colloidal spirals in nematic liquid crystals.

    PubMed

    Senyuk, Bohdan; Pandey, Manoj B; Liu, Qingkun; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-12-01

    One of the central experimental efforts in nematic colloids research aims to explore how the interplay between the geometry of particles along with the accompanying nematic director deformations and defects around them can provide a means of guiding particle self-assembly and controlling the structure of particle-induced defects. In this work, we design, fabricate, and disperse low-symmetry colloidal particles with shapes of spirals, double spirals, and triple spirals in a nematic fluid. These spiral-shaped particles, which are controlled by varying their surface functionalization to provide tangential or perpendicular boundary conditions of the nematic molecular alignment, are found inducing director distortions and defect configurations with non-chiral or chiral symmetry. Colloidal particles also exhibit both stable and metastable multiple orientational states in the nematic host, with a large number of director configurations featuring both singular and solitonic nonsingular topological defects accompanying them, which can result in unusual forms of colloidal self-assembly. Our findings directly demonstrate how the symmetry of particle-generated director configurations can be further lowered, or not, as compared to the low point group symmetry of solid micro-inclusions, depending on the nature of induced defects while satisfying topological constraints. We show that achiral colloidal particles can cause chiral symmetry breaking of elastic distortions, which is driven by complex three-dimensional winding of induced topological line defects and solitons. PMID:26358649

  3. The Spiral-Interactive Program Evaluation Model.

    ERIC Educational Resources Information Center

    Khaleel, Ibrahim Adamu

    1988-01-01

    Describes the spiral interactive program evaluation model, which is designed to evaluate vocational-technical education programs in secondary schools in Nigeria. Program evaluation is defined; utility oriented and process oriented models for evaluation are described; and internal and external evaluative factors and variables that define each…

  4. The Spiral Curriculum. Research into Practice

    ERIC Educational Resources Information Center

    Johnston, Howard

    2012-01-01

    The Spiral Curriculum is predicated on cognitive theory advanced by Jerome Bruner (1960), who wrote, "We begin with the hypothesis that any subject can be taught in some intellectually honest form to any child at any stage of development." In other words, even the most complex material, if properly structured and presented, can be understood by…

  5. SPIRAL2 at GANIL: Status and Perspectives

    SciTech Connect

    Gales, S.

    2008-05-12

    To pursue the investigation of a new territory of nuclei with extreme N/Z called 'terra incognita' several projects, all aiming at the increase by several orders of magnitude of the RIB intensities are now under discussions worldwide. In Europe, two major new projects have been approved recently FAIR-GSI using the so-called 'in-flight' method and SPIRAL2-GANIL, based on the ISOL method. Both projects were selected in the European Strategic Roadmap For research Infrastructures (ESFRI). The main goal of SPIRAL2 is clearly to extend our knowledge of the limit of existence and the structure of nuclei deeply in the medium and heavy mass region (A = 60 to 140) which is to day an almost unexplored continent. SPIRAL 2 is based on a high power, CW, superconducting driver LINAC, delivering 5 mA of deuteron beams at 40 MeV (200 KW) directed on a C converter+ Uranium target and producing therefore more 10{sup 13} fissions/s. The expected radioactive beams intensities for exotic species in the mass range from A = 60 to A = 140, of the order of 10{sup 6} to 10{sup 10} pps will surpass by two order of magnitude any existing facilities in the world. These unstable atoms will be available at energies between few KeV/n to 15 MeV/n. The same driver will accelerate high intensity (100 {mu}A to 1 mA), heavier ions up to Ar at 14 MeV/n producing also proton rich exotic nuclei. In applied areas SPIRAL2 is considered as a powerful variable energy neutron source, a must to study the impact of nuclear fission and fusion on materials. The intensities of these unstable species are excellent opportunities for new tracers and diagnostics either for solid state, material or for radiobiological science and medicine. The 'Go' decision has been taken in May 2005. The investments and personnel costs amount to 190 Meuro, for the construction period 2006-2012. Construction of the SPIRAL2 facility is shared by ten French laboratories and a network of international partners. Under the 7FP program of

  6. Curved spiral antennas for underwater biological applications

    NASA Astrophysics Data System (ADS)

    Llamas, Ruben

    We developed curved spiral antennas for use in underwater (freshwater) communications. Specifically, these antennas will be integrated in so-called mussel backpacks. Backpacks are compact electronics that incorporate sensors and a small radio that operate around 300 MHz. Researchers attach these backpacks in their freshwater mussel related research. The antennas must be small, lightweight, and form-fit the mussel. Additionally, since the mussel orientation is unknown, the antennas must have broad radiation patterns. Further, the electromagnetic environment changes significantly as the mussels burrow into the river bottom. Broadband antennas, such a spiral antennas, will perform better in this instance. While spiral antennas are well established, there has been little work on their performance in freshwater. Additionally, there has been some work on curved spiral antennas, but this work focused on curving in one dimension, namely curving around a cylinder. In this thesis we develop spiral antennas that curve in two dimensions in order to conform the contour of a mussel's shell. Our research has three components, namely (a) an investigation of the relevant theoretical underpinning of spiral antennas, (b) extensive computer simulations using state-of-the art computational electromagnetics (CEM) simulation software, and (c) experimental validation. The experimental validation was performed in a large tank in a laboratory setting. We also validated some designs in a pool (~300,000 liters of water and ~410 squared-meter dive pool) with the aid of a certified diver. To use CEM software and perform successful antenna-related experiments require careful attention to many details. The mathematical description of radiation from an antenna, antenna input impedance and so on, is inherently complex. Engineers often make simplifying assumptions such as assuming no reflections, or an isotropic propagation environment, or operation in the antenna far field, and so on. This makes

  7. Rings and spirals in barred galaxies - II. Ring and spiral morphology

    NASA Astrophysics Data System (ADS)

    Athanassoula, E.; Romero-Gómez, M.; Bosma, A.; Masdemont, J. J.

    2009-12-01

    In this series of papers, we propose a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits guided by the manifolds emanating from the unstable Lagrangian points located near the ends of the bar. In this paper, we focus on a comparison of the morphology of observed and of theoretical spirals and rings and we also give some predictions for further comparisons. Our theory can account for spirals as well as both inner and outer rings. The model outer rings have the observed R1, R'1, R2, R'2 and R1R2 morphologies, including the dimples near the direction of the bar major axis. We explain why the vast majority of spirals in barred galaxies are two armed and trailing, and discuss what it would take for higher multiplicity arms to form. We show that the shapes of observed and theoretical spirals agree and we predict that stronger non-axisymmetric forcings at and somewhat beyond corotation will drive more open spirals. We compare the ratio of ring diameters in theory and in observations and predict that more elliptical rings will correspond to stronger forcings. We find that the model potential may influence strongly the numerical values of these ratios.

  8. GANIL-SPIRAL2: A new era

    SciTech Connect

    Gales, Sydney

    2011-05-06

    GANIL presently offers unique opportunities in nuclear physics and many other fields that arise from not only the provision of low-energy stable beams, fragmentation beams and re-accelerated radioactive species, but also from the availability of a wide range of state-of-the-art spectrometers and instrumentation. A few examples of recent highlights are discussed in the present paper.With the construction of SPIRAL2 over the next few years, GANIL is in a good position to retain its world-leading capability. As selected by the ESFRI committee, the next generation of ISOL facility in Europe is represented by the SPIRAL2 project to be built at GANIL (Caen, France). SPIRAL 2 is based on a high power, CW, superconducting LINAC, delivering 5 mA of deuteron beams at 40 MeV (200 KW) directed on a C converter+ Uranium target and producing therefore more than 10{sup 13} fissions/s. The expected radioactive beam intensities in the mass range from A = 60 to A = 140, will surpass by two orders of magnitude any existing facilities in the world. These unstable atoms will be available at energies between few KeV/n to 15 MeV/n. The same driver will accelerate high intensity (100 {mu}A to 1 mA), heavier ions (Ar up to Xe) at maximum energy of 14 MeV/n. Under the 7FP program of European Union called *Preparatory phase*, the SPIRAL2 project has been granted a budget of about 4MEuro to build up an international consortium around this new venture. The status of the construction of SPIRAL2 accelerator and associated physics instruments in collaboration with EU and International partners will be presented.

  9. [CT fluoroscopy].

    PubMed

    Rogalla, P; Juran, R

    2004-07-01

    Percutaneous biopsy of pulmonary nodules requires precise needle placement, with the goal of attaining a secure position of the needle for therapeutic or diagnostic purposes as quickly as possible and with minimal tissue damage along the access route. The requirements from the image guidance system during the intervention are, in addition to universal applicability, a quick reaction time and a user-friendly interface. CT fluoroscopy fulfils these requirements, although radiation protection for the patient and radiologist becomes an important issue. PMID:15232690

  10. Accessible or Inaccessible? Diagnostic Efficacy of CT-Guided Core Biopsies of Head and Neck Masses

    SciTech Connect

    Cunningham, Jane D. McCusker, Mark W.; Power, Sarah; PearlyTi, Joanna; Thornton, John; Brennan, Paul; Lee, Michael J.; O’Hare, Alan; Looby, Seamus

    2015-04-15

    PurposeTissue sampling of lesions in the head and neck is challenging due to complex regional anatomy and sometimes necessitates open surgical biopsy. However, many patients are poor surgical candidates due to comorbidity. Thus, we evaluated the use of CT guidance for establishing histopathological diagnosis of head and neck masses.MethodsAll consecutive patients (n = 22) who underwent CT-guided core biopsy of head or neck masses between April 2009 and August 2012 were retrospectively reviewed using the departmental CT interventional procedures database. The indication for each biopsy performed was to establish or exclude a diagnosis of neoplasia in patients with suspicious head or neck lesions found on clinical examination or imaging studies. Patients received conscious sedation and 18 G, semiautomated core needle biopsies were performed by experienced neuroradiologists using 16-slice multidetector row CT imaging guidance (Somatom Definition Siemens Medical Solutions, Germany). Histopathology results of each biopsy were analysed.ResultsSixteen of 22 biopsies that were performed (73 %) yielded a pathological diagnosis. Anatomic locations biopsied included: masticator (n = 7), parapharyngeal (n = 3), parotid (n = 3), carotid (n = 3), perivertebral (n = 3), pharyngeal (n = 2), and retropharyngeal (n = 1) spaces. Six biopsies (27 %) were nondiagnostic due to inadequate tissue sampling, particularly small biopsy sample size and failure to biopsy the true sampling site due to extensive necrosis. No major complications were encountered.ConclusionsThe use of CT guidance to perform core biopsies of head and neck masses is an effective means of establishing histopathological diagnosis and reduces the need for diagnostic open surgical biopsy and general anaesthesia.

  11. Circularly polarized unidirectional emission via a coupled plasmonic spiral antenna.

    PubMed

    Rui, Guanghao; Nelson, Robert L; Zhan, Qiwen

    2011-12-01

    In this Letter, we study the emission properties of an electric dipole emitter coupled to a plasmonic spiral structure. The plasmonic spiral structure functions as an optical antenna, coupling the electric dipole emission into circularly polarized unidirectional emission in the far field. Increasing number of turns of the spiral leads to narrower angular width of the emission pattern in the far field. For a spiral antenna with six turns, antenna directivity of 23.5 dB with a directional emission into a narrow angular cone of 4.3° can be achieved. The emitted photons carry spin that is essentially determined by the handedness of the spiral antenna. By reversing the spiral, one can switch the polarization of the emission field between left-hand and right-hand circular polarizations. The spiral antenna may be used as a nanoscale circular polarization source in single molecule sensing, single-photo sources, and integrated photonic circuits. PMID:22139233

  12. Effect of lateral target motion on image registration accuracy in CT-guided helical tomotherapy: a phantom study.

    PubMed

    Medwig, J; Gaede, S; Battista, J J; Yartsev, S

    2010-06-01

    Optimisation of imaging modes for kilovoltage CT (kVCT) used for treatment planning and megavoltage CT (MVCT) image guidance used in ungated helical tomotherapy was investigated for laterally moving targets. Computed tomography images of the QUASAR Respiratory Motion Phantom were acquired without target motion and for lateral motion of the target, with 2-cm peak-to-peak amplitude and a period of 4 s. Reference kVCT images were obtained using a 16-slice CT scanner in standard fast helical CT mode, untagged average CT mode and various post-processed 4D-CT modes (0% phase, average and maximum intensity projection). Three sets of MVCT images with different inter-slice spacings of were obtained on a Hi-Art tomotherapy system with the phantom displaced by a known offset position. Eight radiation therapists performed co-registration of MVCT obtained with 2-, 4- and 6-mm slice spacing and kVCT studies independently for all 15 CT imaging combinations. In the investigated case, the untagged average kVCT and 4-mm slice spacing for the MVCT yielded more accurate registration in the transverse plane. The average residual uncertainty of this combination of imaging procedures was 0.61 +/- 0.16 mm in the longitudinal direction, 0.45 +/- 0.14 mm in the anterior-posterior direction and insignificant in the lateral direction. Manual registration of MVCT-kVCT study pairs is necessary to account for a target in significant lateral motion with respect to bony structures. PMID:20598016

  13. Flash imaging in dual source CT (DSCT)

    NASA Astrophysics Data System (ADS)

    Bruder, H.; Petersilka, M.; Mehldau, H.; Heidinger, W.; Allmendinger, T.; Schmidt, B.,; Raupach, R.; Thierfelder, C.,; Stierstorfer, K.; Flohr, T.

    2009-02-01

    We present new acquisition modes of a recently introduced dual-source computed tomography (DSCT) system equipped with two X-ray tubes and two corresponding detectors, mounted onto the rotating gantry with an angular offset of typically 90°. Due to the simultaneous acquisition of complementary data, the minimum exposure time is reduced by a factor of two compared to a single-source CT system (SSCT). The correspondingly improved temporal resolution is beneficial for cardiac CT. Also, maximum table feed per rotation in a spiral mode can be increased by a factor of 2 compared to SSCT, which provides benefits both for cardiac CT and non-cardiac CT. In an ECG-triggered mode the entire cardiac volume can be scanned within a fraction of one cardiac RR-cycle. At a rotation time of 0.28s using a detector with 64×0.6 mm beam collimation, the scan time of the entire heart is less than 0.3s at a temporal resolution of 75 ms. It will be shown, that the extremely fast cardiac scan reduces the patient dose to a theoretical lowest limit: for a 120 kV scan the dose level for a typical cardiac CT scan is well below 2 mSv. Using further protocol optimization (scan range adaptation, 100kV), the radiation dose can be reduced below 1mSv.

  14. Implementation of propeller, spiral, and variable density spiral methods for dynamic contrast enhanced magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Ahunbay, Ergun Emin

    2001-09-01

    Previous studies showed that dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is a valuable tool for the prognosis and diagnosis of cancer, however it requires a tradeoff between temporal and spatial resolution. The ultimate goal of this dissertation is to compare the temporal performance of three methods (spiral, propeller and variable density spiral), given a certain spatial resolution requirement, for the DCE-MRI. These methods show distinction from the conventional MRI methods in their k-space coverage. Propeller and Variable Density Spiral methods use an approach of oversampling the center of k-space, updating the central 13-20% of the radial k-space more frequently than the peripheries. The reason for this is that most of the image data resides in the central part of k-space. Spiral method, on the other hand approaches the problem by updating the overall k-space as fast as possible, faster than the conventional methods. Comparison is performed mainly by computer simulations, where ground truth is known. In addition to computer simulations, these three methods are compared in- vivo, by tracking the DCE-MRI signal amplitude variation with time for each method on a healthy volunteer's liver. One limitation of the spiral and variable density spiral imaging methods is the effect of off-resonance frequencies on image quality. For these spiral based methods, long readout times are desired to have short overall imaging times and high temporal resolution. However, for long readout times, off resonance frequencies blur the images and reduce the spatial resolution. In this dissertation a new method is proposed which is less complicated than most other methods, and reaches an acceptable level of accuracy with less amount of CPU time compared to previously effective methods.

  15. 64-Slice spiral computed tomography and three-dimensional reconstruction in the diagnosis of cystic pancreatic tumors

    PubMed Central

    WEN, ZHAOXIA; YAO, FENGQING; WANG, YUXING

    2016-01-01

    The present study aimed to describe the characteristics of cystic pancreatic tumors using computed tomography (CT) and to evaluate the diagnostic accuracy (DA) of post-imaging three-dimensional (3D) reconstruction. Clinical and imaging data, including multi-slice spiral CT scans, enhanced scans and multi-faceted reconstruction, from 30 patients with pathologically confirmed cystic pancreatic tumors diagnosed at the Linyi People's Hospital between August 2008 and June 2014 were retrospectively analyzed. Following the injection of Ultravist® 300 contrast agent, arterial, portal venous and parenchymal phase scans were obtained at 28, 60 and 150 sec, respectively, and 3D reconstructions of the CT images were generated. The average age of the patients was 38.4 years (range, 16–77 years), and the cohort included 5 males and 25 females (ratio, 1:5). The patients included 8 cases of mucinous cystadenoma (DA), 80%]; 9 cases of cystadenocarcinoma (DA, 84%); 6 cases of serous cystadenoma (DA, 100%); 3 cases of solid pseudopapillary tumor (DA, 100%); and 4 cases of intraductal papillary mucinous neoplasm (DA, 100%). 3D reconstructions of CT images were generated and, in the 4 cases of intraductal papillary mucinous neoplasm, the tumor was connected to the main pancreatic duct and multiple mural nodules were detected in one of these cases. The DA of the 3D-reconstructed images of cystic pancreatic tumors was 89.3%. The 64-slice spiral CT and 3D-reconstructed CT images facilitated the visualization of cystic pancreatic tumor characteristics, in particular the connections between the tumor and the main pancreatic duct. In conclusion, the 3D reconstruction of multi-slice CT data may provide an important source of information for the surgical team, in combination with the available clinical data. PMID:27073473

  16. Spiral precipitation patterns in confined chemical gardens

    PubMed Central

    Haudin, Florence; Brau, Fabian; De Wit, A.

    2014-01-01

    Chemical gardens are mineral aggregates that grow in three dimensions with plant-like forms and share properties with self-assembled structures like nanoscale tubes, brinicles, or chimneys at hydrothermal vents. The analysis of their shapes remains a challenge, as their growth is influenced by osmosis, buoyancy, and reaction–diffusion processes. Here we show that chemical gardens grown by injection of one reactant into the other in confined conditions feature a wealth of new patterns including spirals, flowers, and filaments. The confinement decreases the influence of buoyancy, reduces the spatial degrees of freedom, and allows analysis of the patterns by tools classically used to analyze 2D patterns. Injection moreover allows the study in controlled conditions of the effects of variable concentrations on the selected morphology. We illustrate these innovative aspects by characterizing quantitatively, with a simple geometrical model, a new class of self-similar logarithmic spirals observed in a large zone of the parameter space. PMID:25385581

  17. Stationary spiral flow in polytropic stellar models

    SciTech Connect

    Pekeris, C.L.

    1980-06-01

    It is shown that, in addition to the static Emden solution, a self-gravitating polytropic gas has a dynamic option in which there is stationary flow along spiral trajectories wound around the surfaces of concentric tori. The motion is obtained as a solution of a partial differential equation which is satisfied by the meridional stream function, coupled with Poisson's equation and a Bernoulli-type equation for the pressure (density). The pressure is affected by the whole of the Bernoulli term rather than by the centrifugal part only, which acts for a rotating model, and it may be reduced down to zero at the center. The spiral type of flow is illustrated for an incompressible fluid (n = 0), for which an exact solution is obtained. The features of the dynamic constant-density model are discussed as a basis for future comparison with the solution for compressible models.

  18. Star formation and evolution in spiral galaxies.

    NASA Technical Reports Server (NTRS)

    Quirk, W. J.; Tinsley, B. M.

    1973-01-01

    Evolutionary models for regions of M31 and M33 and the solar neighborhood are based on a stellar birthrate suggested by the dynamics of spiral structure: we assume that stars are formed very efficiently until the gas content reaches equilibrium at its present value, which takes about 1 b.y.; thereafter, the birthrate just equals the rate at which gas enters the system from stellar mass-loss or infall of intergalactic matter. Each model represents an average around a cylindrical-shell-shaped region, which is homogeneous and closed except for possible infall. The disk and spiral-arm populations only are considered. Each star is followed in the H-R diagram from the main sequence to death as an invisible remnant. Integrated magnitudes, colors, mass-to-light ratio (M/L), gas content, helium and metal abundance (Z), are computed in steps of 1 b.y.

  19. Spiral precipitation patterns in confined chemical gardens.

    PubMed

    Haudin, Florence; Cartwright, Julyan H E; Brau, Fabian; De Wit, A

    2014-12-01

    Chemical gardens are mineral aggregates that grow in three dimensions with plant-like forms and share properties with self-assembled structures like nanoscale tubes, brinicles, or chimneys at hydrothermal vents. The analysis of their shapes remains a challenge, as their growth is influenced by osmosis, buoyancy, and reaction-diffusion processes. Here we show that chemical gardens grown by injection of one reactant into the other in confined conditions feature a wealth of new patterns including spirals, flowers, and filaments. The confinement decreases the influence of buoyancy, reduces the spatial degrees of freedom, and allows analysis of the patterns by tools classically used to analyze 2D patterns. Injection moreover allows the study in controlled conditions of the effects of variable concentrations on the selected morphology. We illustrate these innovative aspects by characterizing quantitatively, with a simple geometrical model, a new class of self-similar logarithmic spirals observed in a large zone of the parameter space. PMID:25385581

  20. Status of the SPIRAL2 injector commissioning

    NASA Astrophysics Data System (ADS)

    Thuillier, T.; Angot, J.; Barué, C.; Bertrand, P.; Biarrotte, J. L.; Canet, C.; Denis, J.-F.; Ferdinand, R.; Flambard, J.-L.; Jacob, J.; Jardin, P.; Lamy, T.; Lemagnen, F.; Maunoury, L.; Osmond, B.; Peaucelle, C.; Roger, A.; Sole, P.; Touzery, R.; Tuske, O.; Uriot, D.

    2016-02-01

    The SPIRAL2 injector, installed in its tunnel, is currently under commissioning at GANIL, Caen, France. The injector is composed of two low energy beam transport lines: one is dedicated to the light ion beam production, the other to the heavy ions. The first light ion beam, created by a 2.45 GHz electron cyclotron resonance ion source, has been successfully produced in December 2014. The first beam of the PHOENIX V2 18 GHz heavy ion source was analyzed on 10 July 2015. A status of the SPIRAL2 injector commissioning is given. An upgrade of the heavy ion source, named PHOENIX V3 aimed to replace the V2, is presented. The new version features a doubled plasma chamber volume and the high charge state beam intensity is expected to increase by a factor of 1.5 to 2 up to the mass ˜50. A status of its assembly is proposed.

  1. Status of the SPIRAL2 injector commissioning.

    PubMed

    Thuillier, T; Angot, J; Barué, C; Bertrand, P; Biarrotte, J L; Canet, C; Denis, J-F; Ferdinand, R; Flambard, J-L; Jacob, J; Jardin, P; Lamy, T; Lemagnen, F; Maunoury, L; Osmond, B; Peaucelle, C; Roger, A; Sole, P; Touzery, R; Tuske, O; Uriot, D

    2016-02-01

    The SPIRAL2 injector, installed in its tunnel, is currently under commissioning at GANIL, Caen, France. The injector is composed of two low energy beam transport lines: one is dedicated to the light ion beam production, the other to the heavy ions. The first light ion beam, created by a 2.45 GHz electron cyclotron resonance ion source, has been successfully produced in December 2014. The first beam of the PHOENIX V2 18 GHz heavy ion source was analyzed on 10 July 2015. A status of the SPIRAL2 injector commissioning is given. An upgrade of the heavy ion source, named PHOENIX V3 aimed to replace the V2, is presented. The new version features a doubled plasma chamber volume and the high charge state beam intensity is expected to increase by a factor of 1.5 to 2 up to the mass ∼50. A status of its assembly is proposed. PMID:26931951

  2. ON THE FRACTION OF BARRED SPIRAL GALAXIES

    SciTech Connect

    Nair, Preethi B.; Abraham, Roberto G. E-mail: abraham@astro.utoronto.c

    2010-05-10

    We investigate the stellar masses of strongly barred spiral galaxies. Our analysis is based on a sample of {approx}14,000 visually classified nearby galaxies given by Nair and Abraham. The fraction of barred spiral galaxies is found to be a strong function of stellar mass and star formation history, with a minimum near the characteristic mass at which bimodality is seen in the stellar populations of galaxies. We also find that bar fractions are very sensitive to the central concentration of galaxies below the transition mass but not above it. This suggests that whatever process is causing the creation of the red and blue sequences is either influencing, or being influenced by, structural changes which manifest themselves in the absence of bars. As a consequence of strong bar fractions being sensitive to the mass range probed, our analysis helps resolve discrepant results on the reported evolution of bar fractions with redshift.

  3. Spark gap switch with spiral gas flow

    DOEpatents

    Brucker, John P.

    1989-01-01

    A spark gap switch having a contaminate removal system using an injected gas. An annular plate concentric with an electrode of the switch defines flow paths for the injected gas which form a strong spiral flow of the gas in the housing which is effective to remove contaminates from the switch surfaces. The gas along with the contaminates is exhausted from the housing through one of the ends of the switch.

  4. STAR FORMATION IN TWO LUMINOUS SPIRAL GALAXIES

    SciTech Connect

    Hunter, Deidre A.; Ashburn, Allison; Wright, Teresa; Elmegreen, Bruce G.; Rubin, Vera C.; Józsa, Gyula I. G.; Struve, Christian

    2013-10-01

    We examined star formation in two very luminous (M{sub V} = –22 to –23) Sc-type spiral galaxies, NGC 801 and UGC 2885, using ultra-deep Hα images. We combine these Hα images with UBV and Two-Micron All-Sky Survey JHK images and H I maps to explore the star formation characteristics of disk galaxies at high luminosity. Hα traces star formation in these galaxies to 4-6 disk scale lengths, but the lack of detection of Hα further out is likely due to the loss of Lyman continuum photons. Considering gravitational instabilities alone, we find that the gas and stars in the outer regions are marginally stable in an average sense, but considering dissipative gas and radial and azimuthal forcing, the outer regions are marginally unstable to forming spiral arms. Star formation is taking place in spiral arms, which are regions of locally higher gas densities. Furthermore, we have traced smooth exponential stellar disks over four magnitudes in V-band surface brightness and 4-6 disk scale lengths, in spite of a highly variable gravitational instability parameter. Thus, gravitational instability thresholds do not seem relevant to the stellar disk. One possibility for creating an exponential disk is that the molecular cloud densities and star formation rates have exponential profiles and this fact forces the stellar disk to build up such a profile. Another possibility is that the stellar disk is continuously adjusted to an exponential shape regardless of the star formation profile, for example, through global dynamical processes that scatter stars. However, such scattering processes are only known to operate in spiral systems, in which case they cannot explain the same dilemma of smooth exponential disks observed in dwarf irregular galaxies.

  5. Spiral lead platen robotic end effector

    NASA Technical Reports Server (NTRS)

    Beals, David C. (Inventor)

    1990-01-01

    A robotic end effector is disclosed which makes use of a rotating platen with spiral leads used to impact lateral motion to gripping fingers. Actuation is provided by the contact of rolling pins with the walls of the leads. The use of the disclosed method of actuation avoids jamming and provides excellent mechanical advantage while remaining light in weight and durable. The entire end effector is compact and easily adapted for attachment to robotic arms currently in use.

  6. A Fermat's spiral multifilament-core fiber

    NASA Astrophysics Data System (ADS)

    Tartara, L.; Codemard, C.

    2013-02-01

    A multifilament-core optical fiber where the microstructure is arranged in a Fermat's spiral is presented. The properties of such a fiber to be exploited for laser light amplification are numerically investigated by means of a full-vectorial finite-element method. Thanks to this peculiar microstructure, the fiber is shown to have an increased Brillouin threshold power and very low bending losses, while preserving a very good beam spatial quality.

  7. Spiraling Fermi arcs in Weyl materials

    NASA Astrophysics Data System (ADS)

    Li, Songci; Andreev, Anton

    In Weyl materials the valence and conduction electron bands touch at an even number of isolated points in the Brillouin zone. In the vicinity of these points the electron dispersion is linear and may be described by the massless Dirac equation. This results in nontrivial topology of Berry connection curvature. One of its consequences is the existence of peculiar surface electron states whose Fermi surfaces form arcs connecting projections of the Weyl points onto the surface plane. Band bending near the boundary of the crystal also produces surface states. We show that in Weyl materials band bending near the crystal surface gives rise to spiral structure of energy surfaces of arc states. The corresponding Fermi surface has the shape of a spiral that winds about the projection of the Weyl point onto the surface plane. The direction of the winding is determined by the helicity of the Weyl point and the sign of the band bending potential. For close valleys arc state morphology may be understood in terms of avoided crossing of oppositely winding spirals. This work is supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences under Award Number DE-FG02-07ER46452.

  8. Basis for Synthesis of Spiral Lattice Quasicrystals

    NASA Astrophysics Data System (ADS)

    Bursill, L. A.; Ryan, George; Fan, Xudong; Rouse, J. L.; Peng, Julin; Perkins, Anne

    Observations of the sunflower Helianthus tuberosus reveal the occurrence of both Fibonacci and Lucas numbers of visible spirals (parastichies). This species is multi-headed, allowing a quantitative study of the relative abundance of these two types of phyllotaxis. The florets follow a spiral arrangement. It is remarkable that the Lucas series occurred, almost invariably, in the first-flowering heads of individual plants. The occurrence of left-and right-handed chirality was found to be random, within experimental error, using an appropriate chirality convention. Quantitative crystallographic studies allow the average growth law to be derived (r = alτ-1 θ = 2πl/(τ + 1), where a is a constant, l is the seed cell number and τ is the golden mean (1 +√ {5})/2). They also reveal departures from classical theoretical models of phyllotaxis, taking the form of persistent oscillations in both divergence angle and radius. The experimental results are discussed in terms of a new theoretical model for the close-packing of growing discs. Finally, a basis for synthesis of (inorganic) spiral lattice structures is proposed.

  9. A new spiral model for Saturn's magnetosphere

    NASA Astrophysics Data System (ADS)

    Carbary, J. F.

    2016-01-01

    Rather than a clock-like strobe, a rotating spiral may underlie the ~10.7 h periodicities observed in many phenomena in Saturn's magnetosphere. This spiral is a density or flux wave propagating outward from the planet, and the periodicity is generated when a spacecraft encounters the wave. The wave moves outward with the Alfvén speed, which can be computed from the magnetic field strength and plasma mass density. Using data from the first 200 days of 2010, the observed field strength and plasma density are used to compute this speed and construct the spiral. When the Cassini spacecraft "flies through" this model on a real trajectory, the model produces a strong main period at 10.7 h with weaker secondary periods at 10.4 h and 11.0 h resulting from Doppler effects. Periodograms of observed phenomena from the same interval show a main peak at 10.7 h but with spurious secondary peaks due to noise.

  10. Image quality and diagnostic accuracy of non-invasive coronary imaging with 16 detector slice spiral computed tomography with 188 ms temporal resolution

    PubMed Central

    Kuettner, A; Beck, T; Drosch, T; Kettering, K; Heuschmid, M; Burgstahler, C; Claussen, C D; Kopp, A F; Schroeder, S

    2005-01-01

    Objective: To evaluate image quality and clinical accuracy in detecting coronary artery lesions with a new multidetector spiral computed tomography (MDCT) generation with 16 detector slices and a temporal resolution of 188 ms. Methods: 124 consecutive patients scheduled for invasive coronary angiography (ICA) were additionally studied by MDCT (Sensation 16 Speed 4D). MDCTs were analysed with regard to image quality and presence of coronary artery lesions. The results were compared with ICA. Results: 120 of 124 scans were successful. The image quality of all remaining 120 scans was sufficient (mean (SD) heart rate 64.2 (9.8) beats/min, range 43–95). The mean calcium mass was 167 (223) mg (range 0–1038). Thirteen coronary segments were evaluated for each patient (1560 segments in total). Image quality was graded as follows: excellent, 422 (27.1%) segments; good, 540 (34.6%) segments; moderate, 277 (17.7%) segments; heavily calcified, 215 (13.8%) segments; and blurred, 106 (6.8%) segments. ICA detected 359 lesions with a diameter stenosis > 50% and MDCT detected 304 of 359 (85%). Sensitivity, specificity, and positive and negative predictive values were 85%, 98%, 91%, and 96%, respectively. The correct clinical diagnosis (presence or absence of at least one stenosis > 50%) was obtained for 110 of 120 (92%) patients. Conclusions: MDCT image quality can be further improved with 16 slices and faster gantry rotation time. These results in an unselected population underline the potential of MDCT to become a non-invasive diagnostic alternative, especially for the exclusion of coronary artery disease, in the near future. PMID:15958366

  11. Theoretical study of electron tunneling through the spiral molecule junctions along spiral paths.

    PubMed

    Xu, Xiaodong; Li, Weiqi; Zhou, Xin; Wang, Qiang; Feng, Jikang; Tian, Wei Quan; Jiang, Yongyuan

    2016-02-01

    The electronic transport properties of carbohelicenes and heterohelicenes absorbed between two metal electrodes have been investigated by using the nonequilibrium Green's function in combination with the density function theory. The transport properties of the molecular junctions are mainly dependent on the nature of spiral molecules. The detailed analyses of the transmission spectra, the energy levels as well as the spatial distribution of molecular projected self-consistent Hamiltonian explain how the geometry of molecules affects the intra-molecular electronic coupling. The spiral current in the configurations can be achieved by tuning the outer edge states of spiral-shaped molecules. Furthermore, the symmetric current-voltage characteristics are investigated with the bias changing for all devices as well as an negative differential resistance behavior is observed. PMID:26762548

  12. SU-E-I-25: Determining Tube Current, Tube Voltage and Pitch Suitable for Low- Dose Lung Screening CT

    SciTech Connect

    Williams, K; Matthews, K

    2014-06-01

    Purpose: The quality of a computed tomography (CT) image and the dose delivered during its acquisition depend upon the acquisition parameters used. Tube current, tube voltage, and pitch are acquisition parameters that potentially affect image quality and dose. This study investigated physicians' abilities to characterize small, solid nodules in low-dose CT images for combinations of current, voltage and pitch, for three CT scanner models. Methods: Lung CT images was acquired of a Data Spectrum anthropomorphic torso phantom with various combinations of pitch, tube current, and tube voltage; this phantom was used because acrylic beads of various sizes could be placed within the lung compartments to simulate nodules. The phantom was imaged on two 16-slice scanners and a 64-slice scanner. The acquisition parameters spanned a range of estimated CTDI levels; the CTDI estimates from the acquisition software were verified by measurement. Several experienced radiologists viewed the phantom lung CT images and noted nodule location, size and shape, as well as the acceptability of overall image quality. Results: Image quality for assessment of nodules was deemed unsatisfactory for all scanners at 80 kV (any tube current) and at 35 mA (any tube voltage). Tube current of 50 mA or more at 120 kV resulted in similar assessments from all three scanners. Physician-measured sphere diameters were closer to actual diameters for larger spheres, higher tube current, and higher kV. Pitch influenced size measurements less for larger spheres than for smaller spheres. CTDI was typically overestimated by the scanner software compared to measurement. Conclusion: Based on this survey of acquisition parameters, a low-dose CT protocol of 120 kV, 50 mA, and pitch of 1.4 is recommended to balance patient dose and acceptable image quality. For three models of scanners, this protocol resulted in estimated CTDIs from 2.9–3.6 mGy.

  13. Super-spiral structures in an excitable medium

    NASA Astrophysics Data System (ADS)

    Perez-Muñuzuri, V.; Aliev, R.; Vasiev, B.; Perez-Villar, V.; Krinsky, V. I.

    1991-10-01

    ROTATING spiral waves have been observed in various excitable media, including heart muscle1, retinae2, cultures of the slime mould Dyctiostelium discoideum3,4 and chemical oscillators such as the Belousov-Zhabotinsky (BZ) reaction5-7. Under certain conditions the spiral wave does not exhibit simple periodic rotation, but quasiperiodic8 (or 'compound'9) rotation, in which the spiral's origin (the tip) meanders10. Recent calculations11 have shown that highly meandering tip motion can impose superstructures on spiral waves. Here we reproduce these patterns experimentally, using the BZ reaction as the excitable medium. We induce high tip meander by applying pulses of electrical current locally at the tip12. Image processing of the patterns reveals a spiral wave of larger wavelength superimposed on the original wave, an effect that can be described in terms of a Doppler shift in the original spiral.

  14. Nonlinear dynamics of breathers in the spiral structures of magnets

    NASA Astrophysics Data System (ADS)

    Kiselev, V. V.; Raskovalov, A. A.

    2016-06-01

    The structure and properties of pulsating solitons (breathers) in the spiral structures of magnets are analyzed within the sine-Gordon model. The breather core pulsations are shown to be accompanied by local shifts and oscillations of the spiral structure with the formation of "precursors" and "tails" in the moving soliton. The possibilities for the observation and excitation of breathers in the spiral structures of magnets and multiferroics are discussed.

  15. On a new coordinate system with astrophysical application: Spiral coordinates

    NASA Astrophysics Data System (ADS)

    Campos, L. M. B. C.; Gil, P. J. S.

    In this presentation are introduced spiral coordinates, which are a particular case of conformal coordinates, i.e. orthogonal curvelinear coordinates with equal factors along all coordinate axis. The spiral coordinates in the plane have as coordinate curves two families of logarithmic spirals, making a constant angle, respectively phi and pi / 2-phi, with all radial lines, where phi is a parameter. They can be obtained from a complex function, representing a spiral potential flow, due to the superposition of a source/sink with a vortex; the parameter phi in this case specifies the ratio of the ass flux of source/sink to the circulation of the vortex. Regardless of hydrodynamical or other interpretations, spiral coordinates are particulary convenient in situation where physical quantities vary only along a logarithmicspiral. The example chosen is the propagation of Alfven waves along a logarithmic spiral, as an approximation to Parker's spiral. The equation of dissipative MHD are written in spiral coordinates, and eliminated to specify the Alfven wave equation in spiral coordinates; the latter is solved exactly in terms of Bessel functions, and the results analyzed for values of the parameters corresponding to the solar wind.

  16. Influence of excitability on unpinning and termination of spiral waves.

    PubMed

    Luengviriya, Jiraporn; Sutthiopad, Malee; Phantu, Metinee; Porjai, Porramain; Kanchanawarin, Jarin; Müller, Stefan C; Luengviriya, Chaiya

    2014-11-01

    Application of electrical forcing to release pinned spiral waves from unexcitable obstacles and to terminate the rotation of free spiral waves at the boundary of excitable media has been investigated in thin layers of the Belousov-Zhabotinsky (BZ) reaction, prepared with different initial concentrations of H_{2}SO_{4}. Increasing [H_{2}SO_{4}] raises the excitability of the reaction and reduces the core diameter of free spiral waves as well as the wave period. An electric current with density stronger than a critical value Junpin causes a pinned spiral wave to drift away from the obstacle. For a given obstacle size, Junpin increases with [H_{2}SO_{4}]. Under an applied electrical current, the rotation center of a free spiral wave drifts along a straight path to the boundary. When the current density is stronger than a critical value Jterm, the spiral tip is forced to hit the boundary, where the spiral wave is terminated. Similar to Junpin for releasing a pinned spiral wave, Jterm also increases with [H_{2}SO_{4}]. These experimental findings were confirmed by numerical simulations using the Oregonator model, in which the excitability was adjusted via the ratio of the excitation rate to the recovery rate of the BZ reaction. Therefore, our investigation shows that decreasing the excitability can facilitate elimination of spiral waves by electrical forcing, either in the presence of obstacles or not. PMID:25493870

  17. STAR CLUSTERS IN PSEUDOBULGES OF SPIRAL GALAXIES

    SciTech Connect

    Di Nino, Daiana; Trenti, Michele; Stiavelli, Massimo; Carollo, C. Marcella; Scarlata, Claudia; Wyse, Rosemary F. G.

    2009-11-15

    We present a study of the properties of the star-cluster systems around pseudobulges of late-type spiral galaxies using a sample of 11 galaxies with distances from 17 Mpc to 37 Mpc. Star clusters are identified from multiband Hubble Space Telescope ACS and WFPC2 imaging data by combining detections in three bands (F435W and F814W with ACS and F606W with WFPC2). The photometric data are then compared to population synthesis models to infer the masses and ages of the star clusters. Photometric errors and completeness are estimated by means of artificial source Monte Carlo simulations. Dust extinction is estimated by considering F160W NICMOS observations of the central regions of the galaxies, augmenting our wavelength coverage. In all galaxies we identify star clusters with a wide range of ages, from young (age {approx}< 8 Myr) blue clusters, with typical mass of 10{sup 3} M {sub sun} to older (age >100-250 Myr), more massive, red clusters. Some of the latter might likely evolve into objects similar to the Milky Way's globular clusters. We compute the specific frequencies for the older clusters with respect to the galaxy and bulge luminosities. Specific frequencies relative to the galaxy light appear consistent with the globular cluster specific frequencies of early-type spirals. We compare the specific frequencies relative to the bulge light with the globular cluster specific frequencies of dwarf galaxies, which have a surface brightness profile that is similar to that of the pseudobulges in our sample. The specific frequencies we derive for our sample galaxies are higher than those of the dwarf galaxies, supporting an evolutionary scenario in which some of the dwarf galaxies might be the remnants of harassed late-type spiral galaxies that hosted a pseudobulge.

  18. Bezoar-induced small bowel obstruction: Clinical characteristics and diagnostic value of multi-slice spiral computed tomography

    PubMed Central

    Wang, Pei-Yuan; Wang, Xia; Zhang, Lin; Li, Hai-Fei; Chen, Liang; Wang, Xu; Wang, Bin

    2015-01-01

    AIM: To determine the possible predisposing factors of bezoar-induced small bowel obstruction (BI-SBO) and to discuss the diagnostic value of multi-slice spiral computed tomography, particularly contrast-enhanced scanning, in this condition. METHODS: A total of 35 BI-SBO cases treated at our hospital from January 2007 to December 2013 were retrospectively analysed. Complete clinical and computed tomography (CT) data of the patients were available and confirmed by surgery. SBO was clinically diagnosed on the basis of clinical manifestations. Of the 35 patients, 18 underwent abdominal and pelvic CT planar scanning with GE 64-slice spiral CT and 17 underwent abdominal and pelvic CT planar scanning with GE 64-slice spiral CT combined with contrast-enhanced examination. Original images were processed using a GE ADW4.3 workstation to obtain MPR, CPR, MIP and CTA images. The images of all patients were evaluated by two abdominal imaging experts. The main analytical contents of planar scanning included intestinal bezoar conditions, changes in the intestinal wall and changes in peri-intestinal conditions. Vascular hyperaemia and arterial blood supply conditions at a specific obstruction site and the distal end of the obstruction site were evaluated through contrast-enhanced examination. RESULTS: The proportion of males to females among the 35 cases was 1:1.69 (13:22); median age was 63.3 years. The following cases were observed: 29 (82.8%) cases occurred in autumn and winter and showed a history of consuming high amounts of persimmon and hawthorn; 19 (54.3%) cases revealed a history of gastrointestinal surgery; 19 exhibited incomplete dentition, with missing partial or whole posterior teeth; 26 suffered from obstruction at the ileum. A total of 51 bezoars were found in these patients, of whom 16 (45.7%) had multiple bezoars. CT planar scanning of bezoars showed lumps with mottled gas inside the intestinal cavity. Furthermore, 9 cases of bezoars had envelopes and 11 cases

  19. Bailey, Butler, McFarland: Discovery of Spiral Nebulae: Unwinding the discovery of spiral nebulae

    NASA Astrophysics Data System (ADS)

    Bailey, M. E.; Butler, C. J.; McFarland, J.

    2005-04-01

    Evidence for spiral structure in distant galaxies was first noticed by William Parsons, the Third Earl of Rosse, in April 1845 within a few months of the first trial of his great six-foot reflector the ``Leviathan of Parsonstown'' on 11 February 1845. Despite the significance of this discovery there are puzzling inconsistencies in the story, and the discovery date - sometime in April - is curiously vague. Here we review the chronology of observations of the two principal players in the story: Messier 51 and Messier 99. The former was identified by Lord Rosse as having a spiral arrangement in the spring of 1845, and the latter ``the following spring''. The Revd Thomas Romney Robinson, the third Director of the Armagh Observatory, was observing with Lord Rosse during February and March 1845, and again in 1848, but he apparently only confirmed Rosse's detection of spirality in both galaxies around 11 March 1848. No-one doubted Lord Rosse's discovery of spirality in M51 (and the following year also in M99), but it was almost three years before the observation was confirmed by another astronomer.

  20. Spiral structure of M51: Streaming motions across the spiral arms

    NASA Technical Reports Server (NTRS)

    Tilanus, R. P. J.; Allen, R. J.

    1990-01-01

    The atomic hydrogen (HI) and the H alpha emission line in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the Taurus Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H alpha emission after subtraction of the axi-symmetric component of the velocity field. The shift is positive on the inside and negative on the outside of the northern arm. Across the southern arm this situation is reversed. The direction of the shifts is such that the material is moving inward and faster compared to circular rotation in both arms, consistent with the velocity perturbations predicted by spiral density wave models for gas downstream of a spiral shock. The observed shifts amount to 20 to 30 km (s-1), corresponding to streaming motions of 60 to 90 km (s-1) in the plane of the disk (inclination angle 20 degrees). Comparable velocity gradients have also been observed by Vogel et al. in the CO emission from the inner northern arm of M51. The streaming motions in M51 are about 2 to 3 times as large as the ones found in HI by Rots in M81, and successfully modelled by Visser with a self-consistent density wave model. Researchers have not been able to detect conclusively streaming motions in the HI emission from the arms, perhaps due to the relatively poor angular resolution (approx. 15 seconds) of the HI observations.

  1. Dark and visible matter in spiral galaxies

    NASA Technical Reports Server (NTRS)

    Persic, M.; Salucci, P.

    1988-01-01

    Rotation-curve profiles are used to determine the dark-to-luminous mass ratio within the disk size for 43 spiral galaxies. It is noted that faint galaxies are halo-dominated and that bright galaxies are disk-dominated in the disk regions. The luminosity sequence is shown to be a dark-to-luminous sequence. By removing the dark-matter contribution from the velocity at the disk edge, the dispersion affecting the luminosity-kinematics relation is found to decrease in comparison with the conventional Tully-Fisher correlation.

  2. MAGNIFICENT DETAILS IN A DUSTY SPIRAL GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. An international team of astronomers, led by Dr. Wendy Freedman of the Observatories of the Carnegie Institution of Washington, observed this galaxy on 13 different occasions over the course of two months. Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters. Based on their discovery and careful brightness measurements of variable stars in NGC 4414, the Key Project astronomers were able to make an accurate determination of the distance to the galaxy. The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself. Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust

  3. THE DYNAMICS OF SPIRAL ARMS IN PURE STELLAR DISKS

    SciTech Connect

    Fujii, M. S.; Baba, J.; Saitoh, T. R.; Makino, J.; Kokubo, E.; Wada, K. E-mail: wada@cfca.jp

    2011-04-01

    It has been believed that spiral arms in pure stellar disks, especially the ones spontaneously formed, decay in several galactic rotations due to the increase of stellar velocity dispersions. Therefore, some cooling mechanism, for example dissipational effects of the interstellar medium, was assumed to be necessary to keep the spiral arms. Here, we show that stellar disks can maintain spiral features for several tens of rotations without the help of cooling, using a series of high-resolution three-dimensional N-body simulations of pure stellar disks. We found that if the number of particles is sufficiently large, e.g., 3 x 10{sup 6}, multi-arm spirals developed in an isolated disk can survive for more than 10 Gyr. We confirmed that there is a self-regulating mechanism that maintains the amplitude of the spiral arms. Spiral arms increase Toomre's Q of the disk, and the heating rate correlates with the squared amplitude of the spirals. Since the amplitude itself is limited by Q, this makes the dynamical heating less effective in the later phase of evolution. A simple analytical argument suggests that the heating is caused by gravitational scattering of stars by spiral arms and that the self-regulating mechanism in pure stellar disks can effectively maintain spiral arms on a cosmological timescale. In the case of a smaller number of particles, e.g., 3 x 10{sup 5}, spiral arms grow faster in the beginning of the simulation (while Q is small) and they cause a rapid increase of Q. As a result, the spiral arms become faint in several Gyr.

  4. Gated CT imaging using a free-breathing respiration signal from flow-volume spirometry

    SciTech Connect

    D'Souza, Warren D.; Kwok, Young; Deyoung, Chad; Zacharapoulos, Nicholas; Pepelea, Mark; Klahr, Paul; Yu, Cedric X.

    2005-12-15

    Respiration-induced tumor motion is known to cause artifacts on free-breathing spiral CT images used in treatment planning. This leads to inaccurate delineation of target volumes on planning CT images. Flow-volume spirometry has been used previously for breath-holds during CT scans and radiation treatments using the active breathing control (ABC) system. We have developed a prototype by extending the flow-volume spirometer device to obtain gated CT scans using a PQ 5000 single-slice CT scanner. To test our prototype, we designed motion phantoms to compare image quality obtained with and without gated CT scan acquisition. Spiral and axial (nongated and gated) CT scans were obtained of phantoms with motion periods of 3-5 s and amplitudes of 0.5-2 cm. Errors observed in the volume estimate of these structures were as much as 30% with moving phantoms during CT simulation. Application of motion-gated CT with active breathing control reduced these errors to within 5%. Motion-gated CT was then implemented in patients and the results are presented for two clinical cases: lung and abdomen. In each case, gated scans were acquired at end-inhalation, end-exhalation in addition to a conventional free-breathing (nongated) scan. The gated CT scans revealed reduced artifacts compared with the conventional free-breathing scan. Differences of up to 20% in the volume of the structures were observed between gated and free-breathing scans. A comparison of the overlap of structures between the gated and free-breathing scans revealed misalignment of the structures. These results demonstrate the ability of flow-volume spirometry to reduce errors in target volumes via gating during CT imaging.

  5. Computed Tomography (CT) - Spine

    MedlinePlus

    ... News Physician Resources Professions Site Index A-Z Computed Tomography (CT) - Spine Computed tomography (CT) of the spine is a diagnostic imaging ... Spine? What is CT Scanning of the Spine? Computed tomography, more commonly known as a CT or CAT ...

  6. Single-slice rebinning method for helical cone-beam CT.

    PubMed

    Noo, F; Defrise, M; Clackdoyle, R

    1999-02-01

    In this paper, we present reconstruction results from helical cone-beam CT data, obtained using a simple and fast algorithm, which we call the CB-SSRB algorithm. This algorithm combines the single-slice rebinning method of PET imaging with the weighting schemes of spiral CT algorithms. The reconstruction is approximate but can be performed using 2D multislice fan-beam filtered backprojection. The quality of the results is surprisingly good, and far exceeds what one might expect, even when the pitch of the helix is large. In particular, with this algorithm comparable quality is obtained using helical cone-beam data with a normalized pitch of 10 to that obtained using standard spiral CT reconstruction with a normalized pitch of 2. PMID:10070801

  7. Residual Stress Measurement Using Rectangular Spiral Coils

    NASA Astrophysics Data System (ADS)

    Sun, Haiyan; Plotnikov, Yuri

    2008-02-01

    Shot peening process provides compressive residual stress within a depth of about 150˜200 um from the surface. It has been demonstrated that multi-frequency eddy current measurement can be effectively used for the residual stress estimation on Ni-based superalloys. In order to measure the stress profile over the entire compressive zone, the probe needs to work in a wide frequency range from 0.1 MHz to above 50 MHz. Due to its wide bandwidth and high precision fabrication process, spiral coils fabricated on flexible substrate using photolithographic technology are good candidate for this task It is useful to develop a coil model in order to optimize coil design, minimize liftoff effect and maximize coil gauge factor. In this work, a 3D analytical model was used to simulate rectangular spiral coil response on a half-space conductor. The results were compared with commercial available 3D finite element software and experimental results. The analytical model was also used to simulate 4-point calibration process that was used to calculate apparent eddy current conductivity (AECC). The experimental setup was described and AECC profile was obtained for shot-peening samples with different peening intensity and different heat treatment.

  8. Spiral Plate Method for Bacterial Determination

    PubMed Central

    Gilchrist, J. E.; Campbell, J. E.; Donnelly, C. B.; Peeler, J. T.; Delaney, J. M.

    1973-01-01

    A method is described for determining the number of bacteria in a solution by the use of a machine which deposits a known volume of sample on a rotating agar plate in an ever decreasing amount in the form of an Archimedes spiral. After the sample is incubated, different colony densities are apparent on the surface of the plate. A modified counting grid is described which relates area of the plate of volume of sample. By counting an appropriate area of the plate, the number of bacteria in the sample is estimated. This method was compared to the pour plate procedure with the use of pure and mixed cultures in water and milk. The results did not demonstrate a significant difference in variance between duplicates at the α = 0.01 level when concentrations of 600 to 12 × 105 bacteria per ml were used, but the spiral plate method gave counts that were higher than counts obtained by the pour plate method. The time and materials required for this method are substantially less than those required for the conventional aerobic pour plate procedure. Images PMID:4632851

  9. Precision of spiral-bevel gears

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Goldrich, R. N.; Coy, J. J.; Zaretsky, E. V.

    1982-01-01

    The kinematic errors in spiral bevel gear trains caused by the generation of nonconjugate surfaces, by axial displacements of the gears during assembly, and by eccentricity of the assembled gears were determined. One mathematical model corresponds to the motion of the contact ellipse across the tooth surface, (geometry I) and the other along the tooth surface (geometry II). The following results were obtained: (1) kinematic errors induced by errors of manufacture may be minimized by applying special machine settings, the original error may be reduced by order of magnitude, the procedure is most effective for geometry 2 gears, (2) when trying to adjust the bearing contact pattern between the gear teeth for geometry 1 gears, it is more desirable to shim the gear axially; for geometry II gears, shim the pinion axially; (3) the kinematic accuracy of spiral bevel drives are most sensitive to eccentricities of the gear and less sensitive to eccentricities of the pinion. The precision of mounting accuracy and manufacture are most crucial for the gear, and less so for the pinion.

  10. Precision of spiral-bevel gears

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Goldrich, R. N.; Coy, J. J.; Zaretsky, E. V.

    1983-01-01

    The kinematic errors in spiral bevel gear trains caused by the generation of nonconjugate surfaces, by axial displacements of the gears during assembly, and by eccentricity of the assembled gears were determined. One mathematical model corresponds to the motion of the contact ellipse across the tooth surface, (geometry I) and the other along the tooth surface (geometry II). The following results were obtained: (1) kinematic errors induced by errors of manufacture may be minimized by applying special machine settings, the original error may be reduced by order of magnitude, the procedure is most effective for geometry 2 gears, (2) when trying to adjust the bearing contact pattern between the gear teeth for geometry I gears, it is more desirable to shim the gear axially; for geometry II gears, shim the pinion axially; (3) the kinematic accuracy of spiral bevel drives are most sensitive to eccentricities of the gear and less sensitive to eccentricities of the pinion. The precision of mounting accuracy and manufacture are most crucial for the gear, and less so for the pinion. Previously announced in STAR as N82-30552

  11. Vertical extensions of galactic spiral arms

    NASA Technical Reports Server (NTRS)

    Soukup, J. E.; Yuan, C.

    1981-01-01

    The vertical structure of the large scale galactic shock along spiral arms is studied in order to understand the extended features or the wings of spiral arms observed by Kepner (1970) and recently checked by Soukup (1979). Numerical calculations of two-dimensional gas flow were performed for two models of the gas. The results show that the shock front, standing perfectly perpendicular to the galactic plane, extends impressively above the scale height of the interstellar gas. In the extreme case of isothermal gas, the shock solution exists at any distance from the plane. In a realistic model in which the kinetic temperature of the gas is stratified, increasing with height, the shock can extend up to 700 pc. For both models, although the velocity component perpendicular to the galactic plane is small, the solutions corresponding to layered one-dimensional flow contain no shocks at such heights. In order to study the geometry of the shock front and the flow pattern near it, a simplified model is adopted, in which the Coriolis force is neglected. However, estimates show that including it will enhance the shock strength. The compression at the shock front makes the gas observable at high latitudes.

  12. Propulsion using the electron spiral toroid

    SciTech Connect

    Seward, Clint

    1998-01-15

    A new propulsion method is proposed which could potentially reduce propellant needed for space travel by three orders of magnitude. It uses the newly patented electron spiral toroid (EST), which stores energy as magnetic field energy. The EST is a hollow toroid of electrons, all spiraling in parallel paths in a thin outer shell. The electrons satisfy the coupling condition, forming an electron matrix. Stability is assured as long as the coupling condition is satisfied. The EST is held in place with a small external electric field; without an external magnetic field. The EST system is contained in a vacuum chamber. The EST can be thought of as an energetic entity, with electrons at 10,000 electron volts. Propulsion would not use combustion, but would heat propellant through elastic collisions with the EST surface and eject them for thrust. Chemical rocket combustion heats propellant to 4000 deg. C; an EST will potentially heat the propellant 29,000 times as much, reducing propellant needs accordingly. The thrust can be turned ON and OFF. The EST can be recharged as needed.

  13. Beautiful math--aesthetic patterns based on logarithmic spirals.

    PubMed

    Xinchang Wang; Peichang Ouyang

    2013-01-01

    A simple, fast method generates various visually appealing spiral patterns. The method is based on the concept that spiral patterns comprise a symmetry group of tilings. It employs invariant mappings and a dynamical system to create seamless colored patterns. PMID:24808127

  14. Analyses of magnetic field in spiral steel pipe

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Huang, Xinjing; Chen, Shili; Guo, Shixu; Jin, Shijiu

    2015-02-01

    In order to confirm the feasibility of identifying the girth welds using the magnetic field in spiral pipelines, the distributions of the magnetic field in spiral steel pipes with different sizes and different magnetizations were analyzed using the equivalent magnetic charge method, and were verified experimentally. The magnetic field inside spiral steel pipes is generally uniform with very small magnetic sudden changes at the spiral welds, whereas the magnetic field near the pipe ends has very big local changes. The size of spiral pipes, including its wall thickness, length, diameter, and the lift-off, has various influences on the local magnetic sudden changes at the spiral welds (LMASW) and the magnetic incremental near the pipe ends (MINPE), whereas the difference between LMASW and MINPE is always quite considerable. The bigger the radial magnetization component is, the bigger the difference between LMASW and MINPE is. When the radial magnetization component is small, changes of the circumferential and axial magnetization components can reduce this difference. Since the magnetizations of each pipe are seldom identical, the magnetic field inside each pipe is usually quite different. Thus there will be a big local magnetic sudden change at the girth weld inside the spiral pipeline, and this sudden change is much stronger than LMASW. Therefore, we can still consider identifying the girth welds using the magnetic field in spiral pipelines to improve the positioning accuracy of the in-pipe detector.

  15. Ray transfer matrix for a spiral phase plate.

    PubMed

    Eggleston, M; Godat, T; Munro, E; Alonso, M A; Shi, H; Bhattacharya, M

    2013-12-01

    We present a ray transfer matrix for a spiral phase plate. Using this matrix we determine the stability of an optical resonator made of two spiral phase plates and trace stable ray orbits in the resonator. Our results should be relevant to laser physics, optical micromanipulation, quantum information, and optomechanics. PMID:24323013

  16. Design considerations for an archimedean slot spiral antenna

    NASA Technical Reports Server (NTRS)

    Nurnberger, Michael W.; Volakis, John L.

    1995-01-01

    The design goal is to develop a 118-157 MHz, vertically polarized, low-profile (or conformal) antenna as a replacement for VHF AM blade antennas on aircraft. This design is to be arrived at by scaling the dimensions of an antenna designed for a center frequency of 1.1 GHz. The design prior to scaling may have the following maximum dimensions: diameter less than 3.70 in. and thickness less than 0.50 in. Although a four-arm spiral design was originally suggested, a two-arm spiral may also be used, as both mode-1 and mode-2 (sum and difference) radiation patterns aren't required. While a four-arm spiral can easily be designed should both sum and difference patterns be required, the two-arm design will provide the required sum pattern and simplify the design problem somewhat: only one feed is required, and the feed area geometry is more straightforward. Polarization requirements dictate that a slot spiral be used, as opposed to a wire spiral. Two similar radiating structures were considered. The first is the standard archimedean spiral antenna. The second is a hollow archimedean spiral antenna, essentially a standard archimedean spiral with the inner portion removed.

  17. Tidal interaction of small satellite galaxies with spiral primaries

    NASA Technical Reports Server (NTRS)

    Byrd, Gene G.

    1988-01-01

    The interaction of the disks of spiral galaxies and small companions is discussed. The gravitational drag effects of the disk on small satellites are of particular interest. Studies of the Andromeda Galaxy and its satellites, M32 and NGC 205, reveal the usefulness of few-body test-particle simulations in explaining many features of spiral galaxies and their satellites.

  18. Spiral shocks in a solar-size accretion disc

    NASA Astrophysics Data System (ADS)

    Harlaftis, E. T.; Steeghs, D.

    Accretion discs are fundamental in understanding astrophysical phenomena such as AGNs, novae outbursts and star formation. In interacting binaries, a compact star accretes matter from a donor star through an accretion disc. The outburst origin (disc or secondary star) and the mechanism for the angular momentum transport of the disc material (`viscosity') are still controversial subjects. The rarely-observed rise to outburst may hold the key to a better understanding. Imaging of the Balmer and He{I} emission lines of the dwarf nova IP Peg, during such a rise to outburst, shows a two-arm spiral pattern on the accretion disc around the white dwarf and provides the first convincing observational evidence for spiral waves in a stellar accretion disc (Steeghs, Harlaftis, Horne, 1997, Nature, submitted). Recent observations during the recent November 1996 outburst (Harlaftis, Steeghs, Horne, Martin, ApJ, 1997, in preparation) also demonstrate spiral arms in high-ionization lines such as HeII and the Bowen fluorescence lines which suggests that the spiral pattern may provide an efficient mechanism for trasport of angular momentum out of the disc through spiral shocks. We discuss the origin and location of the spiral arms. The tidal interaction of the secondary star with the enlarged (0.6 Rodot) outburst disc can raise such spiral waves in the outer disc. Comparison and implications for theories of spiral galaxies and planet formation is briefly outlined.

  19. Spiral blood flow in aorta-renal bifurcation models.

    PubMed

    Javadzadegan, Ashkan; Simmons, Anne; Barber, Tracie

    2016-07-01

    The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta-renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta-renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta-renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries. PMID:26414530

  20. The Responsibility Spiral: A Curriculum Framework for STS Education.

    ERIC Educational Resources Information Center

    Waks, Leonard J.

    1992-01-01

    The responsibility spiral is an organizing framework which helps educators identify, select, organize, and sequence learning experiences to promote understanding in the science-technology-society movement. The article examines the spiral's phases (self-understanding, study and reflection, decision making, responsible action, and integration) and…

  1. Effects of non Newtonian spiral blood flow through arterial stenosis

    NASA Astrophysics Data System (ADS)

    Hasan, Md. Mahmudul; Maruf, Mahbub Alam; Ali, Mohammad

    2016-07-01

    The spiral component of blood flow has both beneficial and detrimental effects in human circulatory system. A numerical investigation is carried out to analyze the effect of spiral blood flow through an axisymmetric three dimensional artery having 75% stenosis at the center. Blood is assumed as a Non-Newtonian fluid. Standard k-ω model is used for the simulation with the Reynolds number of 1000. A parabolic velocity profile with spiral flow is used as inlet boundary condition. The peak values of all velocity components are found just after stenosis. But total pressure gradually decreases at downstream. Spiral flow of blood has significant effects on tangential component of velocity. However, the effect is mild for radial and axial velocity components. The peak value of wall shear stress is at the stenosis zone and decreases rapidly in downstream. The effect of spiral flow is significant for turbulent kinetic energy. Detailed investigation and relevant pathological issues are delineated throughout the paper.

  2. Spiral wave chimeras in locally coupled oscillator systems

    NASA Astrophysics Data System (ADS)

    Li, Bing-Wei; Dierckx, Hans

    2016-02-01

    The recently discovered chimera state involves the coexistence of synchronized and desynchronized states for a group of identical oscillators. In this work, we show the existence of (inwardly) rotating spiral wave chimeras in the three-component reaction-diffusion systems where each element is locally coupled by diffusion. A transition from spiral waves with the smooth core to spiral wave chimeras is found as we change the local dynamics of the system or as we gradually increase the diffusion coefficient of the activator. Our findings on the spiral wave chimera in the reaction-diffusion systems suggest that spiral chimera states may be found in chemical and biological systems that can be modeled by a large population of oscillators indirectly coupled via a diffusive environment.

  3. Advanced magnetorheological damper with a spiral channel bypass valve

    NASA Astrophysics Data System (ADS)

    McLaughlin, G.; Hu, W.; Wereley, N. M.

    2014-05-01

    Magnetorheological (MR) fluid has a yield stress that is readily controllable using an applied magnetic field. MR dampers adjust this yield stress in a magnetic valve to accommodate a wide range of shock or vibration loads. In this study, the performance of an MR damper with a spiral channel bypass valve is examined. Three bypass damper configurations, i.e., a spiral channel, a spiral channel with beads, and a straight channel with beads, are subject to sinusoidal forcing at constant amplitude, while varying frequency, and applied field (current). These configurations are characterized using tortuosity and porosity parameters. The spiral channel without beads had the largest porosity and smallest tortuosity, which produced the smallest damper force, but the widest controllable damping range. The spiral channel with beads had the smallest porosity, and a comparable tortuosity, which produced the largest damping force, but similar controllable damping range to the straight channel with beads.

  4. The Primordial Origin Model of Magnetic Fields in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki; Machida, Mami; Kudoh, Takahiro

    2010-10-01

    We propose a primordial-origin model for composite configurations of global magnetic fields in spiral galaxies. We show that a uniform tilted magnetic field wound up into a rotating disk galaxy can evolve into composite magnetic configurations comprising bisymmetric spiral (S = BSS), axisymmetric spiral (A = ASS), plane-reversed spiral (PR), and/or ring (R) fields in the disk, and vertical (V) fields in the center. By MHD simulations we show that these composite galactic fields are indeed created from a weak primordial uniform field, and that different configurations can co-exist in the same galaxy. We show that spiral fields trigger the growth of two-armed gaseous arms. The centrally accumulated vertical fields are twisted and produce a jet toward the halo. We found that the more vertical was the initial uniform field, the stronger was the formed magnetic field in the galactic disk.

  5. Classical Cepheids and the spiral structure of the milky way

    NASA Astrophysics Data System (ADS)

    Dambis, A. K.; Berdnikov, L. N.; Efremov, Yu. N.; Kniazev, A. Yu.; Rastorguev, A. S.; Glushkova, E. V.; Kravtsov, V. V.; Turner, D. G.; Majaess, D. J.; Sefako, R.

    2015-09-01

    We use data on space distribution of the currently most complete sample of Cepheids with reliable distances (565 stars), located within ~5 kpc from the Sun, to study the spiral pattern of the Milky Way galaxy. We estimate the pitch angle as 9°-10°; the most accurate estimate, i = 9.5° ± 0.1°, was obtained assuming the existence of a global four-armed spiral pattern; the solar phase angle in the spiral pattern is χ⊙ = -121° ± 3°. Comparing positions of the spiral arms delineated by classical Cepheids and galactic masers, with the age difference of these objects in mind, we estimate the rotation angular speed of the spiral pattern to be Ω P = 25.2 ± 0.5 km s-1kpc-1.

  6. Fabrication of Spiral Micro-Coil Utilizing LIGA Process

    NASA Astrophysics Data System (ADS)

    Shimada, Osamu; Kusumi, Shinji; Mekaru, Harutaka; Sato, Noriaki; Shimizu, Masami; Yamashita, Michiru; Hattori, Tadashi

    We developed a method for fabricating a three-dimensional spiral micro-inductor with high inductance using the LIGA process. The spiral inductor created had a diameter of 0.5mm, and a length of 1mm. The width of the spiral line was 10µm, the pitch was 20µm, and the number of turns was 15. It was made of plated copper. The master was a brass round bar coated with PMMA resist. Deep X-ray lithography was employed to fabricate a master for a metallic mold at the NewSUBARU synchrotron radiation facility, University of Hyogo. The inductor core was made of resin by injection molding. It has a spiral micro flute on the surface. We chose the worm injection molding technique in order to avoid the parting line across the spiral line. The worm injection molding was the method─for demolding the work such as that used in loosening a screw.

  7. SELF-PERPETUATING SPIRAL ARMS IN DISK GALAXIES

    SciTech Connect

    D'Onghia, Elena; Vogelsberger, Mark; Hernquist, Lars

    2013-03-20

    The causes of spiral structure in galaxies remain uncertain. Leaving aside the grand bisymmetric spirals with their own well-known complications, here we consider the possibility that multi-armed spiral features originate from density inhomogeneities orbiting within disks. Using high-resolution N-body simulations, we follow the motions of stars under the influence of gravity, and show that mass concentrations with properties similar to those of giant molecular clouds can induce the development of spiral arms through a process termed swing amplification. However, unlike in earlier work, we demonstrate that the eventual response of the disk can be highly non-linear, significantly modifying the formation and longevity of the resulting patterns. Contrary to expectations, ragged spiral structures can thus survive at least in a statistical sense long after the original perturbing influence has been removed.

  8. Dynamics of Non-steady Spiral Arms in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Baba, Junichi; Saitoh, Takayuki R.; Wada, Keiichi

    2013-01-01

    In order to understand the physical mechanisms underlying non-steady stellar spiral arms in disk galaxies, we analyzed the growing and damping phases of their spiral arms using three-dimensional N-body simulations. We confirmed that the spiral arms are formed due to a swing amplification mechanism that reinforces density enhancement as a seeded wake. In the damping phase, the Coriolis force exerted on a portion of the arm surpasses the gravitational force that acts to shrink the portion. Consequently, the stars in the portion escape from the arm, and subsequently they form a new arm at a different location. The time-dependent nature of the spiral arms originates in the continual repetition of this nonlinear phenomenon. Since a spiral arm does not rigidly rotate, but follows the galactic differential rotation, the stars in the arm rotate at almost the same rate as the arm. In other words, every single position in the arm can be regarded as the corotation point. Due to interaction with their host arms, the energy and angular momentum of the stars change, thereby causing radial migration of the stars. During this process, the kinetic energy of random motion (random energy) of the stars does not significantly increase, and the disk remains dynamically cold. Owing to this low degree of disk heating, short-lived spiral arms can recurrently develop over many rotational periods. The resultant structure of the spiral arms in the N-body simulations is consistent with the observational nature of spiral galaxies. We conclude that the formation and structure of spiral arms in isolated disk galaxies can be reasonably understood by nonlinear interactions between a spiral arm and its constituent stars.

  9. DYNAMICS OF NON-STEADY SPIRAL ARMS IN DISK GALAXIES

    SciTech Connect

    Baba, Junichi; Saitoh, Takayuki R.; Wada, Keiichi

    2013-01-20

    In order to understand the physical mechanisms underlying non-steady stellar spiral arms in disk galaxies, we analyzed the growing and damping phases of their spiral arms using three-dimensional N-body simulations. We confirmed that the spiral arms are formed due to a swing amplification mechanism that reinforces density enhancement as a seeded wake. In the damping phase, the Coriolis force exerted on a portion of the arm surpasses the gravitational force that acts to shrink the portion. Consequently, the stars in the portion escape from the arm, and subsequently they form a new arm at a different location. The time-dependent nature of the spiral arms originates in the continual repetition of this nonlinear phenomenon. Since a spiral arm does not rigidly rotate, but follows the galactic differential rotation, the stars in the arm rotate at almost the same rate as the arm. In other words, every single position in the arm can be regarded as the corotation point. Due to interaction with their host arms, the energy and angular momentum of the stars change, thereby causing radial migration of the stars. During this process, the kinetic energy of random motion (random energy) of the stars does not significantly increase, and the disk remains dynamically cold. Owing to this low degree of disk heating, short-lived spiral arms can recurrently develop over many rotational periods. The resultant structure of the spiral arms in the N-body simulations is consistent with the observational nature of spiral galaxies. We conclude that the formation and structure of spiral arms in isolated disk galaxies can be reasonably understood by nonlinear interactions between a spiral arm and its constituent stars.

  10. Diagnosis demystified: CT as diagnostic tool in endodontics

    PubMed Central

    Shruthi, Nagaraja; Sreenivasa Murthy, B V; Sundaresh, K J; Mallikarjuna, Rachappa

    2013-01-01

    Diagnosis in endodontics is usually based on clinical and radiographical presentations, which are only empirical methods. The role of healing profession is to apply knowledge and skills towards maintaining and restoring the patient's health. Recent advances in imaging technologies have added to correct interpretation and diagnosis. CT is proving to be an effective tool in solving endodontic mysteries through its three-dimensional visualisation. CT imaging offers many diagnostic advantages to produce reconstructed images in selected projection and low-contrast resolution far superior to that of all other X-ray imaging modalities. This case report is an endeavour towards effective treatment planning of cases with root fracture, root resorption using spiral CT as an adjuvant diagnostic tool. PMID:23814212

  11. Enhanced automated spiral bevel gear inspection

    NASA Technical Reports Server (NTRS)

    Frint, Harold K.; Glasow, Warren

    1992-01-01

    Presented here are the results of a manufacturing and technology program to define, develop, and evaluate an enhanced inspection system for spiral bevel gears. The method uses a multi-axis coordinate measuring machine which maps the working surface of the tooth and compares it with nominal reference values stored in the machine's computer. The enhanced technique features a means for automatically calculating corrective grinding machine settings, involving both first and second order changes, to control the tooth profile to within specified tolerance limits. This enhanced method eliminates the subjective decision making involved in the tooth patterning method, still in use today, which compares contract patterns obtained when the gear is set to run under light load in a rolling test machine. It produces a higher quality gear with significant inspection time and cost savings.

  12. The spiral curriculum in optometric education.

    PubMed

    Super, S

    1989-10-01

    Optometric education should center around clinical training from the first year and develop within a spiral curriculum as far as possible. This does not eliminate the need for a layered curriculum where basic sciences are considered necessary to further learning but serves to make these sciences more applied and relevant to the study of optometry from the very beginning. A philosophy of science component requires to be integrated in the optometry teaching program so as to provide the student with as wide a range of thinking and problem-solving skills possible, in particular those which relate to optometry in general and clinical learning. Advanced technologies in the areas of computers and video materials as well as modern teaching strategies should be used to make paradigm changes in optometric teaching effective. PMID:2587037

  13. How do spiral troughs form on Mars?

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.

    2004-04-01

    A three-dimensional model for the coupled evolution of ice-surface temperature and elevation in the Martian polar ice caps is presented. The model includes (1) enhanced heat absorption on steep, dust-exposed scarps, (2) accumulation and ablation, and (3) lateral conduction of heat within the ice cap. The model equations are similar to classic equations for excitable media, including nerve fibers and chemical oscillators. In two dimensions, a small zone of initial melting in the model develops into a train of poleward-migrating troughs with widths similar to those observed on Mars. Starting from random initial conditions, the three-dimensional model reproduces spiral waves very similar to those in the north polar ice cap, including secondary features such as gull-wing shaped troughs, bifurcations, and terminations. These results suggest that eolian processes and ice flow may not control trough morphology.

  14. Spiral model pilot project information model

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The objective was an evaluation of the Spiral Model (SM) development approach to allow NASA Marshall to develop an experience base of that software management methodology. A discussion is presented of the Information Model (IM) that was used as part of the SM methodology. A key concept of the SM is the establishment of an IM to be used by management to track the progress of a project. The IM is the set of metrics that is to be measured and reported throughout the life of the project. These metrics measure both the product and the process to ensure the quality of the final delivery item and to ensure the project met programmatic guidelines. The beauty of the SM, along with the IM, is the ability to measure not only the correctness of the specification and implementation of the requirements but to also obtain a measure of customer satisfaction.

  15. Mesoscale Magnetic Structures in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Shukurov, Anvar

    Virtually all spiral galaxies host magnetic fields ordered at scales comparable to the galactic size (Beck et al., 1996; Beck, 2000, 2001). Observations of polarized radio emission at improved resolution and sensitivity have revealed details of the global magnetic structures that can shed new light on the problem of their origin. Reversals of the regular magnetic field along radius and/or azimuth and magnetic arms are such features, whose scale exceeds significantly the correlation scale of interstellar turbulence but remains smaller than the overall galactic dimension. Despite a few decades of debate, there remains doubt as to what features of the observed field could have been inherited from the pre-galactic past, and which have been formed and maintained more recently in a relatively mature galaxy. In what follows, we briefly review the current understanding of the origin of the mesoscale magnetic structures and their implications for the origin of galactic magnetic fields.

  16. Highly nonlinear layered spiral microstructured optical fiber

    NASA Astrophysics Data System (ADS)

    Rodrigues, Sílvia M.; Facão, Margarida M.; Latas, Sofia C.; Ferreira, Mário F.

    2013-08-01

    A layered spiral microstructured optical fiber (LS-MOF) is presented, which offers the possibility of a good control of both the dispersion and the nonlinear properties. The proposed design is analyzed using a finite element method considering silica and air as the materials. Zero dispersion, low confinement loss, and a record value of γ = 70.0 W-1/km for the LS-MOF nonlinear parameter are simultaneously obtained at 1.55 μm, whereas a higher value γ = 169.4 W-1/km can be achieved at 1.06 μm. Our results demonstrate the great potential of the LS-MOF for several nonlinear applications, namely for an efficient generation of the supercontinuum.

  17. Spiral Galaxies in MKW/AWM Clusters

    NASA Astrophysics Data System (ADS)

    Williams, Barbara A.

    1997-03-01

    Observations have been made of the neutral hydrogen content of more than 170 galaxies within MKW 4, MKW 7, MKW 8, MKW 9, MKW 11, AWM 1, AWM 3, AWM 4, and AWM 5. This sample of nine clusters is representative of the general class of poor clusters identified by MKW and AWM in that they all contain D-- or cD--like dominant galaxies at their dynamical centers. We examine the neutral hydrogen (HI) content of the spiral members in these systems as a function of the local and global properties of the cluster, i.e., galaxy density, x-ray intra cluster gas pressure, x-ray and optical luminosities, and compare our findings with the HI properties of similar galaxies in rich clusters and loose groups of galaxies.

  18. Effects of spiral arms on star formation in nuclear rings of barred-spiral galaxies

    SciTech Connect

    Seo, Woo-Young; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.kr

    2014-09-01

    We use hydrodynamic simulations to study the effect of spiral arms on the star formation rate (SFR) in nuclear rings of barred-spiral galaxies. We find that spiral arms can be an efficient means of gas transport from the outskirts to the central parts, provided that the arms are rotating slower than the bar. While the ring star formation in models with no arms or corotating arms is active only during around the bar growth phase, arm-driven gas accretion both significantly enhances and prolongs the ring star formation in models with slow-rotating arms. The arm-enhanced SFR is larger by a factor of ∼3-20 than in the no-arm model, with larger values corresponding to stronger and slower arms. Arm-induced mass inflows also make dust lanes stronger. Nuclear rings in slow-arm models are ∼45% larger than in the no-arm counterparts. Star clusters that form in a nuclear ring exhibit an age gradient in the azimuthal direction only when the SFR is small, whereas no notable age gradient is found in the radial direction for models with arm-induced star formation.

  19. Variable Stars in a Distant Spiral Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    A NASA Hubble Space Telescope (HST) view of the magnificent spiral galaxy NGC 4603, the most distant galaxy in which a special class of pulsating stars called Cepheid variables have been found. It is associated with the Centaurus cluster, one of the most massive assemblages of galaxies in the nearby universe. The Local Group of galaxies, of which the Milky Way is a member, is moving in the direction of Centaurus at a speed of more than a million miles an hour under the influence of the gravitational pull of the matter in that direction. Clusters of young bright blue stars highlight the galaxy's spiral arms. In contrast, red giant stars in the process of dying are also found. Only the very brightest stars in NGC 4603 can be seen individually, even with the unmatched ability of the Hubble Space Telescope to obtain detailed images of distant objects. Much of the diffuse glow comes from fainter stars that cannot be individually distinguished by Hubble. The reddish filaments are regions where clouds of dust obscure blue light from the stars behind them. This galaxy was observed by a team affiliated with the HST Key Project on the Extragalactic Distance Scale. Because NGC 4603 is much farther away than the other galaxies studied with Hubble by the Key Project team, 108 million light-years, its stars appear very faint from the Earth, and so accurately measuring their brightness, as is required for distinguishing the characteristic variations of Cepheids, is extremely difficult. Determining the distance to the galaxy required an unprecedented statistical analysis based on extensive computer simulations.

  20. Studies on Thrust Characteristic of High-Thrust Spiral Motor

    NASA Astrophysics Data System (ADS)

    Kominami, Tsutomu; Fujimoto, Yasutaka

    Linear actuators are used in various industrial applications. Connentional linear actuators are a combination of a rotational motor and a ball screw, a hydraulic actuator, or a linear motor. However, these actuators have some demerits. This paper proposes a spiral motor (SPRM) that comprises a spiral stator and a spiral mover. Owing to its spiral structure, the SPRM can be expected to show better performance as compared to the conventional linear actuator. However, it is not easy to manufacture spiral stators and spiral movers. In this paper, thrust and torque equations derived from a magnetic circuit are introduced. A prototype is developed and its specifications are provided. Sixty fan-shaped stator blocks are mounted on the frame and forty-eight fan-shaped mover blocks with flat surfaces are mounted on the axis. These blocks form an approximately spiral structure. The blocks are not difficult to manufacture. The feasibility of the developed SPRM is confirmed by performing basic experiments. First, the SPRM is driven by using synchronous control. Subsequently, the thrust is measured by a load cell and the thrust constant is determined.

  1. Spiral Waves Triggered by Shadows in Transition Disks

    NASA Astrophysics Data System (ADS)

    Montesinos, Matías; Perez, Sebastian; Casassus, Simon; Marino, Sebastian; Cuadra, Jorge; Christiaens, Valentin

    2016-05-01

    Circumstellar asymmetries such as central warps have recently been shown to cast shadows on outer disks. We investigate the hydrodynamical consequences of such variable illumination on the outer regions of a transition disk, and the development of spiral arms. Using 2D simulations, we follow the evolution of a gaseous disk passively heated by the central star, under the periodic forcing of shadows with an opening angle of ∼28°. With a lower pressure under the shadows, each crossing results in a variable azimuthal acceleration, which in time develops into spiral density waves. Their pitch angles evolve from Π ∼ 15°–22° at the onset, to ∼11°–14°, over ∼65 au to 150 au. Self-gravity enhances the density contrast of the spiral waves, as also reported previously for spirals launched by planets. Our control simulations with unshadowed irradiation do not develop structures, except for a different form of spiral waves seen at later times only in the gravitationally unstable control case. Scattered light predictions in the H-band show that such illumination spirals should be observable. We suggest that spiral arms in the case-study transition disk HD 142527 could be explained as a result of shadowing from the tilted inner disk.

  2. Feathering instability of spiral arms. II. Parameter study

    SciTech Connect

    Lee, Wing-Kit

    2014-09-10

    We report the results of a parameter study of the feathering stability in the galactic spiral arms. A two-dimensional, razor-thin magnetized self-gravitating gas disk with an imposed two-armed stellar spiral structure is considered. Using the formulation developed previously by Lee and Shu, a linear stability analysis of the spiral shock is performed in a localized Cartesian geometry. Results of the parameter study of the base state with a spiral shock are also presented. The single-mode feathering instability that leads to growing perturbations may explain the feathering phenomenon found in nearby spiral galaxies. The self-gravity of the gas, characterized by its average surface density, is an important parameter that (1) shifts the spiral shock farther downstream and (2) increases the growth rate and decreases the characteristic spacing of the feathering structure due to the instability. On the other hand, while the magnetic field suppresses the velocity fluctuation associated with the feathers, it does not strongly affect their growth rate. Using a set of typical parameters of the grand-design spiral galaxy M51 at 2 kpc from the center, the spacing of the feathers with the maximum growth rate is found to be 530 pc, which agrees with the previous observational studies.

  3. Feathering Instability of Spiral Arms. II. Parameter Study

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit

    2014-09-01

    We report the results of a parameter study of the feathering stability in the galactic spiral arms. A two-dimensional, razor-thin magnetized self-gravitating gas disk with an imposed two-armed stellar spiral structure is considered. Using the formulation developed previously by Lee & Shu, a linear stability analysis of the spiral shock is performed in a localized Cartesian geometry. Results of the parameter study of the base state with a spiral shock are also presented. The single-mode feathering instability that leads to growing perturbations may explain the feathering phenomenon found in nearby spiral galaxies. The self-gravity of the gas, characterized by its average surface density, is an important parameter that (1) shifts the spiral shock farther downstream and (2) increases the growth rate and decreases the characteristic spacing of the feathering structure due to the instability. On the other hand, while the magnetic field suppresses the velocity fluctuation associated with the feathers, it does not strongly affect their growth rate. Using a set of typical parameters of the grand-design spiral galaxy M51 at 2 kpc from the center, the spacing of the feathers with the maximum growth rate is found to be 530 pc, which agrees with the previous observational studies.

  4. Processing fine stainless-steel slag using spiral concentration.

    PubMed

    Wolfe, Eric R; Klima, Mark S

    2008-04-01

    In this study, the effectiveness of spiral concentration to process a fine (-1 mm) stainless-steel slag was evaluated. Specifically, testing was conducted to determine the feasibility of producing a high metal content stainless steel product and a low metal content aggregate product. This involved investigating a key operating variable for both five-and seven-turn spiral concentrators. The raw slag and spiral products were characterized to determine their respective size and metal distributions. Separation testing was carried out using the two full-scale spiral concentrators to evaluate the effects of feed solids concentration on spiral performance at solids feed rates ranging from 15 to 30 kg/min. The results indicated that under certain conditions, a high-quality metal fraction could be produced. For example, using the five-turn spiral, a product containing 95% metal was obtained at a low metal recovery. Both spirals were ineffective at concentrating the aggregate fraction. Overall, the feed solids concentration did not significantly affect the quality or recoveries of the products, particularly for feed solids concentrations less than 35% by weight. In order to improve the metal recoveries and to produce a low-metal aggregate material, reprocessing of the product streams and/or additional liberation of the raw slag would be required. PMID:18324536

  5. The thermodynamics of vinca alkaloid-induced tubulin spirals formation.

    PubMed

    Lobert, Sharon; Ingram, Jeffrey W; Correia, John J

    2007-03-01

    Vinca alkaloids are antimitotic, anticancer agents that induce tubulin to form spiral polymers at physiological protein concentrations. We used sedimentation velocity to investigate the effects of six vinca alkaloids on tubulin spiraling. Fitting to a Wyman linkage model reveals a drug dependent change of over two orders of magnitude in spiraling potential, K(1)K(2). Thermodynamic analysis of LnK(1)K(2) data demonstrates large and positive DeltaS values, indicating that tubulin spiral formation is entropically-driven. From the curvature in van't Hoff plots of vinblastine data, we estimate DeltaC(p) for GTP and GDP conditions to be -439 and -396 cal/mol K. Partitioning of DeltaS into the hydrophobic effect, DeltaS(HE), change in rotational/translational freedom, DeltaS(RT) and change in protein conformation, DeltaS(other), demonstrates that the major driving force for tubulin spiral formation is burial of hydrophobic surfaces and that protein conformational changes do not make a significant contribution. Spiraling potential is an indicator of antimitotic activity in vivo, although turbidity studies indicate that there is no correlation between spiraling potential and microtubule inhibition in vitro. Mechanisms that explain this discrepancy are discussed. PMID:16757093

  6. Propagation of spiral waves pinned to circular and rectangular obstacles

    NASA Astrophysics Data System (ADS)

    Sutthiopad, Malee; Luengviriya, Jiraporn; Porjai, Porramain; Phantu, Metinee; Kanchanawarin, Jarin; Müller, Stefan C.; Luengviriya, Chaiya

    2015-05-01

    We present an investigation of spiral waves pinned to circular and rectangular obstacles with different circumferences in both thin layers of the Belousov-Zhabotinsky reaction and numerical simulations with the Oregonator model. For circular objects, the area always increases with the circumference. In contrast, we varied the circumference of rectangles with equal areas by adjusting their width w and height h . For both obstacle forms, the propagating parameters (i.e., wavelength, wave period, and velocity of pinned spiral waves) increase with the circumference, regardless of the obstacle area. Despite these common features of the parameters, the forms of pinned spiral waves depend on the obstacle shapes. The structures of spiral waves pinned to circles as well as rectangles with the ratio w /h ˜1 are similar to Archimedean spirals. When w /h increases, deformations of the spiral shapes are observed. For extremely thin rectangles with w /h ≫1 , these shapes can be constructed by employing semicircles with different radii which relate to the obstacle width and the core diameter of free spirals.

  7. Spiral Waves Triggered by Shadows in Transition Disks

    NASA Astrophysics Data System (ADS)

    Montesinos, Matías; Perez, Sebastian; Casassus, Simon; Marino, Sebastian; Cuadra, Jorge; Christiaens, Valentin

    2016-05-01

    Circumstellar asymmetries such as central warps have recently been shown to cast shadows on outer disks. We investigate the hydrodynamical consequences of such variable illumination on the outer regions of a transition disk, and the development of spiral arms. Using 2D simulations, we follow the evolution of a gaseous disk passively heated by the central star, under the periodic forcing of shadows with an opening angle of ˜28°. With a lower pressure under the shadows, each crossing results in a variable azimuthal acceleration, which in time develops into spiral density waves. Their pitch angles evolve from Π ˜ 15°–22° at the onset, to ˜11°–14°, over ˜65 au to 150 au. Self-gravity enhances the density contrast of the spiral waves, as also reported previously for spirals launched by planets. Our control simulations with unshadowed irradiation do not develop structures, except for a different form of spiral waves seen at later times only in the gravitationally unstable control case. Scattered light predictions in the H-band show that such illumination spirals should be observable. We suggest that spiral arms in the case-study transition disk HD 142527 could be explained as a result of shadowing from the tilted inner disk.

  8. NIR properties of isolated spirals with and without an AGN

    NASA Astrophysics Data System (ADS)

    Márquez, Isabel; Durret, Florence; Masegosa, Josefa; Moles, Mariano

    We analyze here the morphological and photometrical properties of a sample of isolated spirals with (18) and without (11) an active nucleus, based on near-infrared imaging in the J and K' bands. No difference is found between the properties of bulges, disks and bars of active and non-active galaxies. Central colors (the innermost 200 pc) of active galaxies are redder that the centers of non-active spirals. Secondary bars are not ubiquitous. Recent numerical simulations seem to be able to account for those active, barred galaxies with no secondary bar, either by means of nuclear spirals or by the direct effect of the primary bar.

  9. Optimal multiobjective design of digital filters using spiral optimization technique.

    PubMed

    Ouadi, Abderrahmane; Bentarzi, Hamid; Recioui, Abdelmadjid

    2013-01-01

    The multiobjective design of digital filters using spiral optimization technique is considered in this paper. This new optimization tool is a metaheuristic technique inspired by the dynamics of spirals. It is characterized by its robustness, immunity to local optima trapping, relative fast convergence and ease of implementation. The objectives of filter design include matching some desired frequency response while having minimum linear phase; hence, reducing the time response. The results demonstrate that the proposed problem solving approach blended with the use of the spiral optimization technique produced filters which fulfill the desired characteristics and are of practical use. PMID:24083108

  10. A Software Development Simulation Model of a Spiral Process

    NASA Technical Reports Server (NTRS)

    Mizell, Carolyn; Malone, Linda

    2007-01-01

    There is a need for simulation models of software development processes other than the waterfall because processes such as spiral development are becoming more and more popular. The use of a spiral process can make the inherently difficult job of cost and schedule estimation even more challenging due to its evolutionary nature, but this allows for a more flexible process that can better meet customers' needs. This paper will present a discrete event simulation model of spiral development that can be used to analyze cost and schedule effects of using such a process in comparison to a waterfall process.

  11. Spiral waves in oscillatory media with an applied electric field

    NASA Astrophysics Data System (ADS)

    Gabbay, Michael; Ott, Edward; Guzdar, Parvez N.

    1999-02-01

    Spiral waves in oscillatory reaction-diffusion systems under the influence of a uniform, time-independent electric field are modeled by the complex Ginzburg-Landau equation extended to include a convective term with complex coefficient. Results for the spiral drift, deformation, and frequency shift due to the electric field are obtained. The coefficient of the additional convective term is derived from the original reaction-diffusion system. The equation provides a good qualitative model of experimentally seen distortion of spiral waves in the presence of an applied electric field.

  12. The accuracy of single emulsion radiographic film in linear measurement of spiral tomography

    PubMed Central

    Dabbaghi, Arash; Shokraneh, Ali; Farhadi, Nastaran

    2013-01-01

    Background: Conventional tomography used for evaluation of the small areas of the jaws provides acceptable information. It has some advantages of availability, less radiation dose and cost in comparison to computed tomography (CT) and cone beam CT. Double emulsion film usually used for taking tomograms requires less exposure than single emulsion film; on the other hand, the latter provides more sharpness and spatial resolution. The aim of this study was to compare diagnostic accuracy of these two kinds of films in the spiral tomography. Materials and Methods: In an experimental study, 20 lines (10 lines anterior and 10 lines posterior to the mental foramen) were selected on two dry human mandibles and tomographic images were taken from each line with and without metal marker by single and double emulsion films. For quantitative assessment, the mandibular width and length was identified and measured on 80obtained tomograms. Afterwards, the mandibles were sectioned on each line and their actual width and height were measured. For each line, the data of tomograms were subtracted from gold standard as measurement error. These errors were divided into three groups: Greater than +1 mm, between +1 mm and −1 mm and less than −1 mm. Obtained data were analyzed by Pearson Chi-square test (α=0/05). Results: There was no significant difference between the single and double emulsion films, with and without markers in the measurement of both height and width of mandible (P > 0.05). Conclusion: The single emulsion film is not recommended to be used for taking the spiral tomogram. PMID:23946736

  13. CT Perfusion of the Liver: Principles and Applications in Oncology

    PubMed Central

    Kim, Se Hyung; Kamaya, Aya

    2014-01-01

    With the introduction of molecularly targeted chemotherapeutics, there is an increasing need for defining new response criteria for therapeutic success because use of morphologic imaging alone may not fully assess tumor response. Computed tomographic (CT) perfusion imaging of the liver provides functional information about the microcirculation of normal parenchyma and focal liver lesions and is a promising technique for assessing the efficacy of various anticancer treatments. CT perfusion also shows promising results for diagnosing primary or metastatic tumors, for predicting early response to anticancer treatments, and for monitoring tumor recurrence after therapy. Many of the limitations of early CT perfusion studies performed in the liver, such as limited coverage, motion artifacts, and high radiation dose of CT, are being addressed by recent technical advances. These include a wide area detector with or without volumetric spiral or shuttle modes, motion correction algorithms, and new CT reconstruction technologies such as iterative algorithms. Although several issues related to perfusion imaging—such as paucity of large multicenter trials, limited accessibility of perfusion software, and lack of standardization in methods—remain unsolved, CT perfusion has now reached technical maturity, allowing for its use in assessing tumor vascularity in larger-scale prospective clinical trials. In this review, basic principles, current acquisition protocols, and pharmacokinetic models used for CT perfusion imaging of the liver are described. Various oncologic applications of CT perfusion of the liver are discussed and current challenges, as well as possible solutions, for CT perfusion are presented. © RSNA, 2014 Online supplemental material is available for this article. PMID:25058132

  14. Head CT (image)

    MedlinePlus

    CT stands for computerized tomography. In this procedure, a thin X-ray beam is rotated around the ... D image of a section through the body. CT scans are very detailed and provide excellent information ...

  15. CT scan (image)

    MedlinePlus

    CT stands for computerized tomography. In this procedure, a thin X-ray beam is rotated around the ... D image of a section through the body. CT scans are very detailed and provide excellent information ...

  16. CT appearance of splenosis

    SciTech Connect

    Mendelson, D.S.; Cohen, B.A.; Armas, R.R.

    1982-12-01

    Splenosis is an unusual complication of splenic trauma. The computed tomographic (CT) appearance of splenosis is described. One should consider this diagnosis when faced with a history of splenic trauma and multiple round or oval masses at CT.

  17. NETL CT Imaging Facility

    ScienceCinema

    None

    2014-05-21

    NETL's CT Scanner laboratory is equipped with three CT scanners and a mobile core logging unit that work together to provide characteristic geologic and geophysical information at different scales, non-destructively.

  18. NETL CT Imaging Facility

    SciTech Connect

    2013-09-04

    NETL's CT Scanner laboratory is equipped with three CT scanners and a mobile core logging unit that work together to provide characteristic geologic and geophysical information at different scales, non-destructively.

  19. Orbit CT scan

    MedlinePlus

    ... results may mean: Bleeding Broken eye socket bone Graves disease Infection Tumor Risks CT scans and other x- ... Livingstone; 2014:chap 66. Read More CT scan Graves disease Tumor Update Date 1/18/2015 Updated by: ...

  20. Spiral formation at microscale by μ-pyro-electrospinning

    NASA Astrophysics Data System (ADS)

    Mecozzi, L.; Gennari, O.; Rega, R.; Grilli, S.; Bhowmick, S.; Gioffrè, M. A.; Coppola, G.; Ferraro, P.

    2016-05-01

    Spiral shapes occur frequently in nature, such as in case of snail shells or in case of the so-called cochlea, namely the auditory portion of the inner ear. They also inspire many technological devices that take advantage of this geometry. Here we show that μ-pyro electrospinning is able to control the whipping instabilities in order to form polymeric spirals directly onto the target support and with true regularity at microscale. The results show that the polymer concentration plays a key role in producing reliable and long spirals. We investigate the cell response to these spiral templates that, thanks to their true regularity, would be useful for developing innovative cochlea regeneration scaffolds.

  1. Topological Signatures in the Electronic Structure of Graphene Spirals

    PubMed Central

    Avdoshenko, Stas M.; Koskinen, Pekka; Sevinçli, Haldun; Popov, Alexey A.; Rocha, Claudia G.

    2013-01-01

    Topology is familiar mostly from mathematics, but also natural sciences have found its concepts useful. Those concepts have been used to explain several natural phenomena in biology and physics, and they are particularly relevant for the electronic structure description of topological insulators and graphene systems. Here, we introduce topologically distinct graphene forms - graphene spirals - and employ density-functional theory to investigate their geometric and electronic properties. We found that the spiral topology gives rise to an intrinsic Rashba spin-orbit splitting. Through a Hamiltonian constrained by space curvature, graphene spirals have topologically protected states due to time-reversal symmetry. In addition, we argue that the synthesis of such graphene spirals is feasible and can be achieved through advanced bottom-up experimental routes that we indicate in this work. PMID:23568379

  2. Anatomy of a Spiral Arm: Gas, Dust and Star Formation

    NASA Astrophysics Data System (ADS)

    Schinnerer, Eva; Meidt, Sharon; Pety, Jerome; Leroy, Adam; Hughes, Annie; Colombo, Dario

    2015-08-01

    Spiral arms can be easily depicted in disk galaxies from the numerous young stars associated with them. However, it is on a fundamental level not clear where, how and when star formation starts relative to the spiral arm. We address these questions by utilizing high 1-3'' resolution observation of the total and dense molecular gas in a spiral arm segment of the nearby grand-design spiral galaxy M51 from PAWS (PdBI Arcsecond Whirlpool Survey) in combination with observations of young stars, HII regions and dust emission. We build a complete picture of the onset, progression and impact of star formation for this segment and discuss this picture in light of theoretical expectations.

  3. 15. April 1963 SPIRAL STAIRS AND EGGSHELL DORMER Shaker ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. April 1963 SPIRAL STAIRS AND EGG-SHELL DORMER - Shaker Centre Family Trustees' Office, South side of Village Road, North of U.S. Route 68 & State Route 33 intersection, Shakertown, Mercer County, KY

  4. Drift laws for spiral waves on curved anisotropic surfaces

    NASA Astrophysics Data System (ADS)

    Dierckx, Hans; Brisard, Evelien; Verschelde, Henri; Panfilov, Alexander V.

    2013-07-01

    Rotating spiral waves organize spatial patterns in chemical, physical, and biological excitable systems. Factors affecting their dynamics, such as spatiotemporal drift, are of great interest for particular applications. Here, we propose a quantitative description for spiral wave dynamics on curved surfaces which shows that for a wide class of systems, including the Belousov-Zhabotinsky reaction and anisotropic cardiac tissue, the Ricci curvature scalar of the surface is the main determinant of spiral wave drift. The theory provides explicit equations for spiral wave drift direction, drift velocity, and the period of rotation. Depending on the parameters, the drift can be directed to the regions of either maximal or minimal Ricci scalar curvature, which was verified by direct numerical simulations.

  5. Drift laws for spiral waves on curved anisotropic surfaces.

    PubMed

    Dierckx, Hans; Brisard, Evelien; Verschelde, Henri; Panfilov, Alexander V

    2013-07-01

    Rotating spiral waves organize spatial patterns in chemical, physical, and biological excitable systems. Factors affecting their dynamics, such as spatiotemporal drift, are of great interest for particular applications. Here, we propose a quantitative description for spiral wave dynamics on curved surfaces which shows that for a wide class of systems, including the Belousov-Zhabotinsky reaction and anisotropic cardiac tissue, the Ricci curvature scalar of the surface is the main determinant of spiral wave drift. The theory provides explicit equations for spiral wave drift direction, drift velocity, and the period of rotation. Depending on the parameters, the drift can be directed to the regions of either maximal or minimal Ricci scalar curvature, which was verified by direct numerical simulations. PMID:23944539

  6. 14. April 1963 SPIRAL STAIRS, DETAIL OF CONSTRUCTION Shaker ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. April 1963 SPIRAL STAIRS, DETAIL OF CONSTRUCTION - Shaker Centre Family Trustees' Office, South side of Village Road, North of U.S. Route 68 & State Route 33 intersection, Shakertown, Mercer County, KY

  7. Equation for the Origin of Spiral Galactic Formation and Rotation

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2012-03-01

    Already formed galactic arms existed in sets of two or more orbiting each other due to the Big Bang. As the orbits of the arms decayed due to gravitational attraction they attached in their fore sections tangentially accreting forming spiral galaxies which began to rotate due to the transformation of the orbital motion of the pre-galactic arms into the rotational motion of the newly formed spiral galaxy. If I1φ1, I2φ2, and Inφn are the angular momentums of the pre-galactic arms, and (Iφ)galaxy is the angular momentum of the newly formed spiral galaxy, the equation for the formation and origin of spiral galaxy rotation is I1φ1+ I2φ2+...+ Inφn= (Iφgalaxy).

  8. Ultraminiature broadband light source with spiral shaped filament

    NASA Technical Reports Server (NTRS)

    Tuma, Margaret L. (Inventor); Collura, Joseph S. (Inventor); Helvajian, Henry (Inventor); Pocha, Michael D. (Inventor); Meyer, Glenn A. (Inventor); McConaghy, Charles F. (Inventor); Olsen, Barry L. (Inventor); Hansen, William W (Inventor)

    2012-01-01

    An ultraminiature light source using a double-spiral shaped tungsten filament includes end contact portions which are separated to allow for radial and length-wise unwinding of the spiral. The double-spiral filament is spaced relatively far apart at the end portions thereof so that contact between portions of the filament upon expansion is avoided. The light source is made by fabricating a double-spiral ultraminiature tungsten filament from tungsten foil and housing the filament in a ceramic package having a reflective bottom and a well wherein the filament is suspended. A vacuum furnace brazing process attaches the filament to contacts of the ceramic package. Finally, a cover with a transparent window is attached onto the top of the ceramic package by solder reflow in a second vacuum furnace process to form a complete hermetically sealed package.

  9. Twin Masks of Spiral Structure? A Local Perspective

    NASA Astrophysics Data System (ADS)

    Steiman-Cameron, Thomas Y.

    We examine models for the spiral structure of the Milky Way proposed over the past half century. Many approaches have been pursued to decipher the geometry of the Galaxy's spiral arms, often with conflicting results. While a general consensus exists that a global pattern exists, considerable disagreement remains in the details. Arm geometries, orientations, and even the number of arms are still debated. Close examination of the literature reveals a clear division between four- and two-arm spiral arms. Four-arm models follow naturally from observations of classical tracers of spiral arms - enhanced gas densities and associated star formation - while two-arm models primarily flow from observations linked to the distribution of cool evolved stars. We examine the dichotomy between two-arm and four-arm models and discuss its implications.

  10. Focusing phenomenon and stability of spiral-flow jet

    NASA Astrophysics Data System (ADS)

    Horii, Kiyoshi; Matsumae, Yuji; Cheng, Xiao M.; Takei, Masahiro; Yasukawa, Eiji

    1991-02-01

    A new nozzle assembly has been developed for an improved focusing of spiral air jet streams. To obtain a focused and highly stable spiral-flow jet, a nozzle is designed with an annular slit connected to a conical cylinder. Pressurized fluid is forced through the sides of the device into the buffer area and then through the annular slit into the pipe entrance. The fluid, passing through the conical cylinder, develops a spiral structure with a steeper axial velocity distribution, caused by Coanda effect and the instability of flow. The jet stream velocity as well as its focusing phenomenon was experimentally determined using a laser sheet method. The results clearly indicate the focusing characteristic and the high stability of spiral flow jet.

  11. Spiral structures in the rotor-router walk

    NASA Astrophysics Data System (ADS)

    Papoyan, Vl V.; Poghosyan, V. S.; Priezzhev, V. B.

    2016-04-01

    We study the rotor-router walk on the infinite square lattice with the outgoing edges at each lattice site ordered clockwise. In the previous paper (Papoyan et al 2015 J. Phys. A: Math. Theor. 48 285203), we considered the loops created by rotors and labeled the sites where the loops become closed. The sequence of labels in the rotor-router walk was conjectured to form a spiral structure asymptotically obeying an Archimedean property. In the present paper, we select a subset of labels called ‘nodes’ and consider the spirals formed by them. The new spirals are directly related to tree-like structures, which represent the evolution of the cluster of vertices visited by the walk. We show that the average number of visits to the origin < {{n}0}(t)> by the moment t\\gg 1 is < {{n}0}(t)> =4< n(t)> +O(1) where < n(t)> is the average number of spiral rotations.

  12. At 1150 Gallery, Block 5, view of top of spiral ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    At 1150 Gallery, Block 5, view of top of spiral stairway, looking west. - Columbia Basin Project, Grand Coulee Dam & Franklin D. Roosevelt Lake, Across Columbia River, Southeast of Town of Grand Coulee, Grand Coulee, Grant County, WA

  13. At 1150 Gallery, Block 5, between spiral stairways, looking southwest. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    At 1150 Gallery, Block 5, between spiral stairways, looking southwest. - Columbia Basin Project, Grand Coulee Dam & Franklin D. Roosevelt Lake, Across Columbia River, Southeast of Town of Grand Coulee, Grand Coulee, Grant County, WA

  14. At 1150 Gallery, Block 5, view of spiral stairway leading ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    At 1150 Gallery, Block 5, view of spiral stairway leading to 1200 Gallery, looking south. - Columbia Basin Project, Grand Coulee Dam & Franklin D. Roosevelt Lake, Across Columbia River, Southeast of Town of Grand Coulee, Grand Coulee, Grant County, WA

  15. Data Fusion Tool for Spiral Bevel Gear Condition Indicator Data

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Antolick, Lance J.; Branning, Jeremy S.; Thomas, Josiah

    2014-01-01

    Tests were performed on two spiral bevel gear sets in the NASA Glenn Spiral Bevel Gear Fatigue Test Rig to simulate the fielded failures of spiral bevel gears installed in a helicopter. Gear sets were tested until damage initiated and progressed on two or more gear or pinion teeth. During testing, gear health monitoring data was collected with two different health monitoring systems. Operational parameters were measured with a third data acquisition system. Tooth damage progression was documented with photographs taken at inspection intervals throughout the test. A software tool was developed for fusing the operational data and the vibration based gear condition indicator (CI) data collected from the two health monitoring systems. Results of this study illustrate the benefits of combining the data from all three systems to indicate progression of damage for spiral bevel gears. The tool also enabled evaluation of the effectiveness of each CI with respect to operational conditions and fault mode.

  16. Effects of abnormal excitation on the dynamics of spiral waves

    NASA Astrophysics Data System (ADS)

    Min-Yi, Deng; Xue-Liang, Zhang; Jing-Yu, Dai

    2016-01-01

    The effect of physiological and pathological abnormal excitation of a myocyte on the spiral waves is investigated based on the cellular automaton model. When the excitability of the medium is high enough, the physiological abnormal excitation causes the spiral wave to meander irregularly and slowly. When the excitability of the medium is low enough, the physiological abnormal excitation leads to a new stable spiral wave. On the other hand, the pathological abnormal excitation destroys the spiral wave and results in the spatiotemporal chaos, which agrees with the clinical conclusion that the early after depolarization is the pro-arrhythmic mechanism of some anti-arrhythmic drugs. The mechanisms underlying these phenomena are analyzed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11365003 and 11165004).

  17. VIEW FROM THE GENERATOR FLOOR LOOKING DOWN AT THE SPIRAL ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    VIEW FROM THE GENERATOR FLOOR LOOKING DOWN AT THE SPIRAL DISTRIBUTOR AND DRAFT CONE. - Wilson Dam & Hydroelectric Plant, Turbine & Generator Unit, Spanning Tennessee River at Wilson Dam Road (Route 133), Muscle Shoals, Colbert County, AL

  18. A new planar feed for slot spiral antennas

    NASA Technical Reports Server (NTRS)

    Nurnberger, M. W.; Volakis, J. L.

    1995-01-01

    This report presents a new planar, wideband feed network for a slot spiral antenna, and the subsequent design and performance of a VHF antenna utilizing this feed design. Both input impedance and radiation pattern measurements are presented to demonstrate the performance and usefulness of this feed. Almost all previous designs have utilized wire spirals, requiring bulky, non-planar feeds with separate baluns, and large absorbing cavities. The presented slot spiral antenna feed integrates the balun into the structure of the slot spiral antenna, making the antenna and feed planar. This greatly simplifies the design and construction of the antenna, in addition to providing repeatable accuracy. It also allows the use of a very shallow reflecting cavity for conformal applications. Finally, this feeding approach now makes many of the known miniaturization techniques viable options.

  19. Internal Extinction in Spiral Galaxies. Inclination Dependence

    NASA Astrophysics Data System (ADS)

    Magris, G. C.; Bruzual, G. A.

    1987-05-01

    . Kent (1986) finds that the surface brightness profiles (r) of spiral galaxies have a weak dependence, if any, on the inclination e with respect to the line of sight. This author also finds a correlation between the MIL ratio and the inclination of a galaxy. The lack of dependence of (r) in , = cos 8 indicates that the disk of these galaxies is optically thick ( .>l), due to the presence of dust grains. For an optically thick system o(r) a + 2.5 log . The cosecant law : 1.086 (Holmberg, 1975) does not explain the observed behaviour of a(r) with . 8ru'ual, Magris and Calvet (1986) solved the radiative transfer equation for a mixture of stars and dispersive dust grains distributed homogeneously in a plane parallel configuration, taking into account the wavelenght dependence of the albedo and , as well as the redistribution in angle of photons scattered by dust grains. The transfer equation is solved for the dimensionless intensity ?( , ) I( , )/I*, where 1* is the intensity emerging from the dust free configuration. The solution, CA -2.5 log (r..=0, ) , includes the correction to the galaxy magnitude due to the excess number 0+ stellar sources along the line o+ sigth (cc -i) with respect to the =I case (face on galaxy). For optically thick systems, does not depend on . The luminosity of a disk galaxy observed with inclination ,q 1 given in our model by L cc , from which log(M/L) = const + (.4 8.N( )'. with G.N . ) = -2.5 log( ). The constant is determined from the mass- luminosity. ratio of a dust free system. In terms of the correction (3(N) we can explain Kent's observations with values of between .3 and 4. These values are consistent with the observation of . -independent surface brightness profiles mentioned above. From this analysis we conclude that the correction terms of Bruzual, Magris and Calvet (1986), which take into account the dispersive properties of interstellar dust, can explain the behaviour of ar) and MIL with galaxy inclination. These correction

  20. Status of the SPIRAL I upgrade at GANIL

    SciTech Connect

    Jardin, P.; Bajeat, O.; Delahaye, P.; Dubois, M.; Feierstein, C.; Pellemoine, F.; Lecomte, P.; Leherissier, P.; Maunoury, L.; Saint-Laurent, M. G.; Traykov, E.

    2012-02-15

    The upgrade of the ''Systeme de Production d'Ions Radioactifs en Ligne'' phase I (SPIRAL I) installed at the ''Grand Accelerateur National d'Ions Lourds'' (GANIL) situated at Caen, France, is in progress and should be ready by 2014. In parallel, the first part of SPIRAL II facility is currently under construction. The global status of the upgrade is presented: goal, radioactive ion production systems, modification of the production cave and impact of the current safety re-evaluation of GANIL.

  1. Face on Barred and Ringed Spiral Galaxy NGC 3351

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Ultraviolet image (left) and visual image (right) of the face on barred and ringed spiral galaxy NGC 3351 (M95). The morphological appearance of a galaxy can change dramatically between visual and ultraviolet wavelengths. In the case of M95, the nucleus and bar dominate the visual image. In the ultraviolet, the bar is not even visible and the ring and spiral arms dominate.

  2. Ideal spiral bevel gears: A new approach to surface geometry

    NASA Technical Reports Server (NTRS)

    Huston, R. L.; Coy, J. J.

    1980-01-01

    The fundamental geometrical characteristics of spiral bevel gear tooth surfaces are discussed. The parametric representation of an ideal spiral bevel tooth is developed based on the elements of involute geometry, differential geometry, and fundamental gearing kinematics. A foundation is provided for the study of nonideal gears and the effects of deviations from ideal geometry on the contact stresses, lubrication, wear, fatigue life, and gearing kinematics.

  3. Marketing cardiac CT programs.

    PubMed

    Scott, Jason

    2010-01-01

    There are two components of cardiac CT discussed in this article: coronary artery calcium scoring (CACS) and coronary computed tomography angiography (CCTA).The distinctive advantages of each CT examination are outlined. In order to ensure a successful cardiac CT program, it is imperative that imaging facilities market their cardiac CT practices effectively in order to gain a competitive advantage in this valuable market share. If patients receive quality care by competent individuals, they are more likely to recommend the facility's cardiac CT program. Satisfied patients will also be more willing to come back for any further testing. PMID:22276376

  4. Validity of spiral analysis in early Parkinson's disease.

    PubMed

    Saunders-Pullman, Rachel; Derby, Carol; Stanley, Kaili; Floyd, Alicia; Bressman, Susan; Lipton, Richard B; Deligtisch, Amanda; Severt, Lawrence; Yu, Qiping; Kurtis, Mónica; Pullman, Seth L

    2008-03-15

    Spiral analysis is an objective, easy to administer noninvasive test that has been proposed to measure motor dysfunction in Parkinson disease (PD). We compared overall Unified Parkinson Disease Rating Scale Part III scores to selected indices derived from spiral analysis in seventy-four patients with early PD (mean duration of disease 2.4 +/- 1.7 years, mean age 61.5 +/- 9.7 years). Of the spiral indices, degree of severity, first order zero crossing, second order smoothness, and mean speed were best correlated with total motor Unified Parkinson's Disease Rating Scale (UPDRS) score (all P < 0.01), and these indices showed a gradient across worsening tertiles of UPDRS (P < 0.05). Spiral indices also correlated with UPDRS ratings for the worst side and worst arm scores as well. The domains of bradykinesia, rigidity, and action tremor were correlated with first order crossing, second order smoothness, and mean speed, where as rest tremor was most highly correlated with degree of severity. This suggests that the spiral analysis may supplement motor assessment in PD, although further analysis of spiral metrics, a larger sample and longitudinal data should be evaluated. PMID:18074362

  5. Comparative properties of Virgo Cluster dwarf irregulars and spirals

    NASA Technical Reports Server (NTRS)

    Hoffman, G. Lyle; Helou, George; Salpeter, E. E.

    1988-01-01

    The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals.

  6. Mechanics and spiral formation in the rat cornea.

    PubMed

    Mohammad Nejad, T; Iannaccone, S; Rutherford, W; Iannaccone, P M; Foster, C D

    2015-01-01

    During the maturation of some mammals such as mice and rats, corneal epithelial cells tend to develop into patterns such as spirals over time. A better understanding of these patterns can help to understand how the organ develops and may give insight into some of the diseases affecting corneal development. In this paper, a framework for explaining the development of the epithelial cells forming spiral patterns due to the effect of tensile and shear strains is proposed. Using chimeric animals, made by combining embryonic cells from genetically distinguishable strains, we can observe the development of patterns in the cornea. Aggregates of cell progeny from one strain or the other called patches form as organs and tissue develop. The boundaries of these patches are fitted with logarithmic spirals on confocal images of adult rat corneas. To compare with observed patterns, we develop a three-dimensional large strain finite element model for the rat cornea under intraocular pressure to examine the strain distribution on the cornea surface. The model includes the effects of oriented and dispersed fibrils families throughout the cornea and a nearly incompressible matrix. Tracing the directions of critical strain vectors on the cornea surface leads to spiral-like curves that are compared to the observed logarithmic spirals. Good agreement between the observed and numerical curves supports the proposed assumption that shear and tensile strains facilitate sliding of epithelial cells to develop spiral patterns. PMID:24897951

  7. Stellar spiral structures in triaxial dark matter haloes

    NASA Astrophysics Data System (ADS)

    Hu, Shaoran; Sijacki, Debora

    2016-09-01

    We employ very high resolution simulations of isolated Milky Way-like galaxies to study the effect of triaxial dark matter haloes on exponential stellar discs. Non-adiabatic halo shape changes can trigger two-armed grand-design spiral structures which extend all the way to the edge of the disc. Their pattern speed coincides with the inner Lindblad resonance indicating that they are kinematic density waves which can persist up to several Gyr. In dynamically cold discs, grand-design spirals are swing amplified and after a few Gyr can lead to the formation of (multi-armed) transient recurrent spirals. Stellar discs misaligned to the principal planes of the host triaxial halo develop characteristic integral shaped warps, but otherwise exhibit very similar spiral structures as aligned discs. For the grand-design spirals in our simulations, their strength dependence with radius is determined by the torque on the disc, suggesting that by studying grand-design spirals without bars it may be possible to set constraints on the tidal field and host dark matter halo shape.

  8. Spiral instabilities in media supporting complex oscillations under periodic forcing

    NASA Astrophysics Data System (ADS)

    Gao, Qingyu; Li, Jun; Zhang, Kailong; Epstein, Irving R.

    2009-09-01

    The periodically forced Brusselator model displays temporal mixed-mode and quasiperiodic oscillations, period doubling, and chaos. We explore the behavior of such media as reaction-diffusion systems for investigating spiral instabilities. Besides near-core breakup and far-field breakup resulting from unstable modes in the radial direction or Doppler-induced instability (destabilization of the core's location), the observed complex phenomena include backfiring, spiral regeneration, and amplitude modulation from line defects. Amplitude modulation of spirals can evolve to chambered spirals resembling those found in nature, such as pine cones and sunflowers. When the forcing amplitude is increased, the spiral-tip meander evolves from simple rotation to complex petals, corresponding to transformation of the local dynamics from simple oscillations to mixed-mode, period-2, and quasiperiodic oscillations. The number of petals is related to the complexity of the mixed-mode oscillations. Spiral turbulence, standing waves, and homogeneous synchronization permeate the entire system when the forcing amplitude is further increased.

  9. CHARACTERISTICS OF SPIRAL ARMS IN LATE-TYPE GALAXIES

    SciTech Connect

    Honig, Z. N.; Reid, M. J.

    2015-02-10

    We have measured the positions of large numbers of H II regions in four nearly face-on, late-type, spiral galaxies: NGC 628 (M74), NGC 1232, NGC 3184, and NGC 5194 (M51). Fitting log-periodic spiral models to segments of each arm yields local estimates of spiral pitch angle and arm width. While pitch angles vary considerably along individual arms, among arms within a galaxy, and among galaxies, we find no systematic trend with galactocentric distance. We estimate the widths of the arm segments from the scatter in the distances of the H II regions from the spiral model. All major arms in these galaxies show spiral arm width increasing with distance from the galactic center, similar to the trend seen in the Milky Way. However, in the outermost parts of the galaxies, where massive star formation declines, some arms reverse this trend and narrow. We find that spiral arms often appear to be composed of segments of ∼5 kpc length, which join to form kinks and abrupt changes in pitch angle and arm width; these characteristics are consistent with properties seen in the large N-body simulations of D'Onghia et al. and others.

  10. Spiral instabilities in media supporting complex oscillations under periodic forcing.

    PubMed

    Gao, Qingyu; Li, Jun; Zhang, Kailong; Epstein, Irving R

    2009-09-01

    The periodically forced Brusselator model displays temporal mixed-mode and quasiperiodic oscillations, period doubling, and chaos. We explore the behavior of such media as reaction-diffusion systems for investigating spiral instabilities. Besides near-core breakup and far-field breakup resulting from unstable modes in the radial direction or Doppler-induced instability (destabilization of the core's location), the observed complex phenomena include backfiring, spiral regeneration, and amplitude modulation from line defects. Amplitude modulation of spirals can evolve to chambered spirals resembling those found in nature, such as pine cones and sunflowers. When the forcing amplitude is increased, the spiral-tip meander evolves from simple rotation to complex petals, corresponding to transformation of the local dynamics from simple oscillations to mixed-mode, period-2, and quasiperiodic oscillations. The number of petals is related to the complexity of the mixed-mode oscillations. Spiral turbulence, standing waves, and homogeneous synchronization permeate the entire system when the forcing amplitude is further increased. PMID:19792014

  11. Recent buckling experiences with spiral wound flexible graphite filled gaskets

    SciTech Connect

    Mueller, R.T.

    1996-12-01

    Given the long and successful history of spiral wound asbestos filled gaskets as widely used in petrochemical plants and refineries, the evolution to flexible graphite filled spiral wound gaskets was expected to be relatively straightforward. For the most part, the transition to flexible graphite has occurred with relatively good success consistent with its improved sealing performance. However, recent experiences reported with buckling type instability problems of flexible graphite filled spiral wound gaskets warrants another look at the industry practices covering this type of gasket. The paper presents findings from 2 different but related instability problems involving spiral would flexible graphite filled gaskets. The first involved Class 1500 and 2500 spiral wound gaskets fitted with inner retaining rings which suffered severe inward buckling with initial boltup. The second experience pertains to Class 600 and lower gaskets supplied without inner retaining rings. Gaskets supplied in both cases complied fully with ASME B16.20 requirements, which highlights possible inadequacies in this standard for spiral wound gaskets. Efforts have been initiated to work with manufacturers in their assessment of fundamental design considerations and with appropriate Code committees to address apparent deficiencies discovered with the industry standards for this type of gasket.

  12. Comparison of CT-Number and Gray Scale Value of Different Dental Materials and Hard Tissues in CT and CBCT

    PubMed Central

    Emadi, Naghmeh; Safi, Yaser; Akbarzadeh Bagheban, Alireza; Asgary, Saeed

    2014-01-01

    Introduction: Computed tomography (CT) and cone-beam CT (CBCT) are valuable diagnostic aids for many clinical applications. This study was designed to compare the gray scale value (GSV) and Hounsfield unit (HU) of selected dental materials and various hard tissues using CT or CBCT. Methods and Materials: Three samples of all test materials including amalgam (AM), composite resin (CR), glass ionomer (GI), zinc-oxide eugenol (ZOE), calcium-enriched mixture (CEM) cement, AH-26 root canal sealer (AH-26), gutta-percha (GP), Coltosol (Col), Dycal (DL), mineral trioxide aggregate (MTA), zinc phosphate (ZP), and polycarbonate cement (PC) were prepared and scanned together with samples of bone, dentin and enamel using two CBCT devices, Scanora 3D (S3D) and NewTom VGi (NTV) and a spiral CT (SCT) scanner (Somatom Emotion 16 multislice spiral CT);. Subsequently, the HU and GSV values were determined and evaluated. The data were analyzed by the Kruskal-Wallis and Mann-Whitney U tests. The level of significance was determined at 0.05. Results: There were significant differences among the three different scanners (P<0.05). The differences between HU/GSV values of 12 selected dental materials using NTV was significant (P<0.05) and for S3D and SCT was insignificant (P>0.05). All tested materials showed maximum values in S3D and SCT (3094 and 3071, respectively); however, bone and dentin showed low/medium values (P<0.05). In contrast, the tested materials and tissues showed a range of values in NTV (366 to15383; P<0.05). Conclusion: Scanner system can influence the obtained HU/GSV of dental materials. NTV can discriminate various dental materials, in contrast to S3D/SCT scanners. NTV may be a more useful diagnostic aid for clinical practice. PMID:25386210

  13. The Nineteenth-Century Spiral Nebula Whodunit

    NASA Astrophysics Data System (ADS)

    Weekes, Trevor C.

    2010-06-01

    The discovery of the first spiral nebula was a milestone in the history of astronomy, but the initial observations of it are shrouded in mystery. The discovery came within months of the commissioning of the Third Earl of Rosse’s very large 72-inch optical telescope at Birr Castle in the center of Ireland. Unfortunately, no observing records have survived, and while there is no doubt that the observations took place in the spring of 1845, there is some uncertainty as to whom was actually present when the discovery was made. The construction of the Earl’s telescope (the Leviathan) was a magnificent achievement, since it was entirely of his design, built with his own funds, and constructed by his own workers who were literally taken “from the plough” on his estate. The summer of 1845 saw the first appearance of the Irish Potato Famine of 1845-1848, which would seriously curtail astronomical activity when Lord Rosse’s 72-inch telescope was in prime condition.

  14. The Hot Gaseous Halos of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Bregman, J.

    2016-06-01

    In the Milky Way, absorption and emission line measurements of O VII and O VIII show that the halo environment is dominated by a nearly spherical halo of temperature 2 × 10^6 K, metallicity of 0.3-0.5 solar, and with a density decreasing as r^{-3/2}. The mass of the hot gas, estimated through extrapolation to the virial radius, is comparable to the stellar mass, but does not account for the missing mass. The Milky Way hot halo appears to be rotating at about 180 km/s, which is consistent with model expectations, depending on the time of infall. Around massive spiral galaxies, hot halos are seen in emission out to about 70 kpc in the best cases. These show similar gas density laws and metallicities in the range 0.1-0.5 solar. The gas mass is comparable to the stellar mass, but does not account for the missing baryons within the virial radius. If the density law can be extrapolated to about three virial radii, the missing baryons would be accounted for.

  15. Chemical evolution in spiral and irregular galaxies

    NASA Technical Reports Server (NTRS)

    Torres-Peimbert, S.

    1986-01-01

    A brief review of models of chemical evolution of the interstellar medium in our galaxy and other galaxies is presented. These models predict the time variation and radial dependence of chemical composition in the gas as function of the input parameters; initial mass function, stellar birth rate, chemical composition of mass lost by stars during their evolution (yields), and the existence of large scale mass flows, like infall from the halo, outflow to the intergalactic medium or radial flows within a galaxy. At present there is a considerable wealth of observational data on the composition of HII regions in spiral and irregular galaxies to constrain the models. Comparisons are made between theory and the observed physical conditions. In particular, studies of helium, carbon, nitrogen and oxygen abundances are reviewed. In many molecular clouds the information we have on the amount of H2 is derived from the observed CO column density, and a standard CO/H2 ratio derived for the solar neighborhood. Chemical evolution models and the observed variations in O/H and N/O values, point out the need to include these results in a CO/H2 relation that should be, at least, a function of the O/H ratio. This aspect is also discussed.

  16. Mapping IR Enhancements in Closely Interacting Spiral-Spiral Pairs: I. ISO CAM and ISO SWS Observations

    NASA Technical Reports Server (NTRS)

    Xu, C.; Gao, Y.; Mazzarella, J.; Lu, N.; Sulentic, J.; Domingue, D.

    2000-01-01

    Mid-infrared (MIR) imaging and spectroscopic observations are presented for a well defined sample of eight closely interacting (CLO) pairs of spiral galaxies that have overlapping disks and show enhanced far-infrared (FIR) emission.

  17. Paleoradiology: advanced CT in the evaluation of nine Egyptian mummies.

    PubMed

    Hoffman, Heidi; Torres, William E; Ernst, Randy D

    2002-01-01

    Axial thin-collimation state-of-the-art spiral computed tomography (CT) was combined with sagittal and coronal reformatting, three-dimensional (3D) reconstruction, and virtual "fly-through" techniques to nondestructively study nine Egyptian mummies. These techniques provided important paleopathologic and historical information about mummification techniques, depicted anatomy in the most informative imaging plane, illustrated the soft-tissue preservation and physical appearance of mummies in superb detail, and generated an intriguing virtual tour through hollow mummified remains without harming the specimens themselves. Images generated with these methods can help archaeologists and Egyptologists understand these fascinating members of mankind and can serve as adjunct visual aids for laypersons who are interested in mummies. CT has emerged as the imaging modality of choice for the examination of Egyptian mummies due to its noninvasive cross-sectional nature and inherently superior contrast and spatial resolution. As multi-detector row CT and postprocessing tools evolve, the capabilities and applications of CT will continue to proliferate, attesting to the expanded versatility and utility of CT as a noninvasive research tool in the multidisciplinary study of Egyptian mummies. PMID:11896227

  18. Spiral structures and regularities in magnetic field variations and auroras

    NASA Astrophysics Data System (ADS)

    Feldstein, Y. I.; Gromova, L. I.; Förster, M.; Levitin, A. E.

    2012-02-01

    The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern

  19. Empirical beam hardening correction (EBHC) for CT

    SciTech Connect

    Kyriakou, Yiannis; Meyer, Esther; Prell, Daniel; Kachelriess, Marc

    2010-10-15

    Purpose: Due to x-ray beam polychromaticity and scattered radiation, attenuation measurements tend to be underestimated. Cupping and beam hardening artifacts become apparent in the reconstructed CT images. If only one material such as water, for example, is present, these artifacts can be reduced by precorrecting the rawdata. Higher order beam hardening artifacts, as they result when a mixture of materials such as water and bone, or water and bone and iodine is present, require an iterative beam hardening correction where the image is segmented into different materials and those are forward projected to obtain new rawdata. Typically, the forward projection must correctly model the beam polychromaticity and account for all physical effects, including the energy dependence of the assumed materials in the patient, the detector response, and others. We propose a new algorithm that does not require any knowledge about spectra or attenuation coefficients and that does not need to be calibrated. The proposed method corrects beam hardening in single energy CT data. Methods: The only a priori knowledge entering EBHC is the segmentation of the object into different materials. Materials other than water are segmented from the original image, e.g., by using simple thresholding. Then, a (monochromatic) forward projection of these other materials is performed. The measured rawdata and the forward projected material-specific rawdata are monomially combined (e.g., multiplied or squared) and reconstructed to yield a set of correction volumes. These are then linearly combined and added to the original volume. The combination weights are determined to maximize the flatness of the new and corrected volume. EBHC is evaluated using data acquired with a modern cone-beam dual-source spiral CT scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany), with a modern dual-source micro-CT scanner (TomoScope Synergy Twin, CT Imaging GmbH, Erlangen, Germany), and with a modern

  20. CT-guided brachytherapy of prostate cancer: reduction of effective dose from X-ray examination

    NASA Astrophysics Data System (ADS)

    Sanin, Dmitriy B.; Biryukov, Vitaliy A.; Rusetskiy, Sergey S.; Sviridov, Pavel V.; Volodina, Tatiana V.

    2014-03-01

    Computed tomography (CT) is one of the most effective and informative diagnostic method. Though the number of CT scans among all radiographic procedures in the USA and European countries is 11% and 4% respectively, CT makes the highest contribution to the collective effective dose from all radiographic procedures, it is 67% in the USA and 40% in European countries [1-5]. Therefore it is necessary to understand the significance of dose value from CT imaging to a patient . Though CT dose from multiple scans and potential risk is of great concern in pediatric patients, this applies to adults as well. In this connection it is very important to develop optimal approaches to dose reduction and optimization of CT examination. International Commission on Radiological Protection (ICRP) in its publications recommends radiologists to be aware that often CT image quality is higher than it is necessary for diagnostic confidence[6], and there is a potential to reduce the dose which patient gets from CT examination [7]. In recent years many procedures, such as minimally invasive surgery, biopsy, brachytherapy and different types of ablation are carried out under guidance of computed tomography [6;7], and during a procedures multiple CT scans focusing on a specific anatomic region are performed. At the Clinics of MRRC different types of treatment for patients with prostate cancer are used, incuding conformal CT-guided brachytherapy, implantation of microsources of I into the gland under guidance of spiral CT [8]. So, the purpose of the study is to choose optimal method to reduce radiation dose from CT during CT-guided prostate brachytherapy and to obtain the image of desired quality.

  1. The Globular Cluster System of the Spiral Galaxy NGC 7814

    NASA Astrophysics Data System (ADS)

    Rhode, Katherine L.; Zepf, Stephen E.

    2003-11-01

    We present the results of a wide-field photometric study of the globular cluster (GC) system of the edge-on Sab spiral NGC 7814. This is the first spiral to be fully analyzed from our survey of the GC systems of a large sample of galaxies beyond the Local Group. NGC 7814 is of particular interest because a previous study estimated that it has 500-1000 GCs, giving it the largest specific frequency (SN) known for a spiral. Understanding this galaxy's GC system is important in terms of our understanding of the GC populations of spirals in general and has implications for the formation of massive galaxies. We observed the galaxy in BVR filters with the WIYN 3.5 m telescope and used image classification and three-color photometry to select GC candidates. We also analyzed archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of NGC 7814, both to help quantify the contamination level of the WIYN GC candidate list and to detect GCs in the inner part of the galaxy halo. Combining HST data with high-quality ground-based images allows us to trace the entire radial extent of this galaxy's GC system and determine the total number of GCs directly through observation. We find that rather than being an especially high-SN spiral, NGC 7814 has <~200 GCs and SN~1, making it comparable to the two most well-studied spiral galaxies, the Milky Way and M31. We explore the implications of these results for models of the formation of galaxies and their GC systems. The initial results from our survey suggest that the GC systems of typical elliptical galaxies can be accounted for by the merger of two or more spirals, but that for highly luminous elliptical galaxies, additional physical processes may be needed.

  2. Clear New View of a Classic Spiral

    NASA Astrophysics Data System (ADS)

    2010-05-01

    ESO is releasing a beautiful image of the nearby galaxy Messier 83 taken by the HAWK-I instrument on ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile. The picture shows the galaxy in infrared light and demonstrates the impressive power of the camera to create one of the sharpest and most detailed pictures of Messier 83 ever taken from the ground. The galaxy Messier 83 (eso0825) is located about 15 million light-years away in the constellation of Hydra (the Sea Serpent). It spans over 40 000 light-years, only 40 percent the size of the Milky Way, but in many ways is quite similar to our home galaxy, both in its spiral shape and the presence of a bar of stars across its centre. Messier 83 is famous among astronomers for its many supernovae: vast explosions that end the lives of some stars. Over the last century, six supernovae have been observed in Messier 83 - a record number that is matched by only one other galaxy. Even without supernovae, Messier 83 is one of the brightest nearby galaxies, visible using just binoculars. Messier 83 has been observed in the infrared part of the spectrum using HAWK-I [1], a powerful camera on ESO's Very Large Telescope (VLT). When viewed in infrared light most of the obscuring dust that hides much of Messier 83 becomes transparent. The brightly lit gas around hot young stars in the spiral arms is also less prominent in infrared pictures. As a result much more of the structure of the galaxy and the vast hordes of its constituent stars can be seen. This clear view is important for astronomers looking for clusters of young stars, especially those hidden in dusty regions of the galaxy. Studying such star clusters was one of the main scientific goals of these observations [2]. When compared to earlier images, the acute vision of HAWK-I reveals far more stars within the galaxy. The combination of the huge mirror of the VLT, the large field of view and great sensitivity of the camera, and the superb observing conditions

  3. Gas velocity patterns in simulated galaxies: Observational diagnostics of spiral structure theories

    NASA Astrophysics Data System (ADS)

    Baba, J.; Morokuma-Matsui, K.; Miyamoto, Y.; Egusa, F.; Kuno, N.

    2016-04-01

    There are two theories of stellar spiral arms in isolated disc galaxies that model stellar spiral arms with different longevities: quasi-stationary density wave theory, which characterises spirals as rigidly rotating, long-lived patterns (i.e. steady spirals), and dynamic spiral theory, which characterises spirals as differentially rotating, transient, recurrent patterns (i.e. dynamic spirals). In order to discriminate between these two spiral models observationally, we investigated the differences between the gas velocity patterns predicted by these two spiral models in hydrodynamic simulations. We found that the azimuthal phases of the velocity patterns relative to the gas density peaks (i.e. gaseous arms) differ between the two models, as do the gas flows; nevertheless, the velocity patterns themselves are similar for both models. Such similarity suggests that the mere existence of streaming motions does not conclusively confirm the steady spiral model. However, we found that the steady spiral model shows that the gaseous arms have radial streaming motions well inside the co-rotation radius, whereas the dynamic spiral model predicts that the gaseous arms tend to have tangential streaming motions. These differences suggest that the gas velocity patterns around spiral arms will enable distinction between the spiral theories.

  4. Gas velocity patterns in simulated galaxies: observational diagnostics of spiral structure theories

    NASA Astrophysics Data System (ADS)

    Baba, J.; Morokuma-Matsui, K.; Miyamoto, Y.; Egusa, F.; Kuno, N.

    2016-08-01

    There are two theories of stellar spiral arms in isolated disc galaxies that model stellar spiral arms with different longevities: quasi-stationary density wave theory, which characterizes spirals as rigidly rotating, long-lived patterns (i.e. steady spirals), and dynamic spiral theory, which characterizes spirals as differentially rotating, transient, recurrent patterns (i.e. dynamic spirals). In order to discriminate between these two spiral models observationally, we investigated the differences between the gas velocity patterns predicted by these two spiral models in hydrodynamic simulations. We found that the azimuthal phases of the velocity patterns relative to the gas density peaks (i.e. gaseous arms) differ between the two models, as do the gas flows; nevertheless, the velocity patterns themselves are similar for both models. Such similarity suggests that the mere existence of streaming motions does not conclusively confirm the steady spiral model. However, we found that the steady spiral model shows that the gaseous arms have radial streaming motions well inside the co-rotation radius, whereas the dynamic spiral model predicts that the gaseous arms tend to have tangential streaming motions. These differences suggest that the gas velocity patterns around spiral arms will enable distinction between the spiral theories.

  5. Characterizing Spiral Arm and Interarm Star Formation

    NASA Astrophysics Data System (ADS)

    Kreckel, K.; Blanc, G. A.; Schinnerer, E.; Groves, B.; Adamo, A.; Hughes, A.; Meidt, S.

    2016-08-01

    Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct Hα maps including detailed corrections for dust extinction and stellar absorption to identify 391 H ii regions at 35 pc resolution over 12 kpc2. Using tracers sensitive to the underlying gravitational potential, we associate H ii regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical properties (luminosity, size, metallicity, ionization parameter) of H ii regions are independent of environment. We calculate the fraction of Hα luminosity due to the background of diffuse ionized gas (DIG) contaminating each H ii region, and find the DIG surface brightness to be higher within H ii regions than in the surroundings, and slightly higher within arm H ii regions. Use of the temperature-sensitive [S ii]/Hα line ratio instead of the Hα surface brightness to identify the boundaries of H ii regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 109 yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H ii regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.

  6. Practical CT dosimetry

    SciTech Connect

    Yoshizumi, T.T.; Suneja, S.K.; Teal, J.S. )

    1989-07-01

    The dose from computed tomography (CT) examinations is not negligible from a radiation safety standpoint. Occasionally, one encounters a case in which an unsuspected pregnant woman undergoes a CT pelvic scan, and the radiologist is required to estimate the dose to the fetus. This article addresses practical methods of CT dosimetry with a specific discussion on fetal dose estimate. Three methods are described: (1) the use of a dose chart, (2) the pencil ionization chamber method, and (3) the thermoluminescence dosimetry (TLD) method.

  7. CT findings in leukemia

    SciTech Connect

    Heiberg, E.; Wolverson, M.K.; Sundaram, M.; Shields, J.B.

    1984-12-01

    Review of 84 computed tomographic (CT) scans in leukemic patients demonstrate a wide spectrum of abnormalities. Findings caused by leukemia were lymphadenopathy, visceral enlargement, focal defects, and tissue infiltration. Hemorrhage was by far the most common complication and could usually be characterized on the noncontrast CT scan. The distinction between old hematomas, foci of infection, and leukemia infiltration could not be made with certainty without CT-guided aspiration. Unusual instances of sepsis, such as microabscesses of the liver and typhlitis, were seen.

  8. PET/CT Artifacts

    PubMed Central

    Blodgett, Todd M.; Mehta, Ajeet S.; Mehta, Amar S.; Laymon, Charles M.; Carney, Jonathan; Townsend, David W.

    2014-01-01

    There are several artifacts encountered in PET/CT imaging, including attenuation correction (AC) artifacts associated with using CT for attenuation correction. Several artifacts can mimic a 2-deoxy-2-[18F] fluoro-D-glucose (FDG) avid malignant lesions and therefore recognition of these artifacts is clinically relevant. Our goal was to identify and characterize these artifacts and also discuss some protocol variables that may affect image quality in PET/CT. PMID:21237418

  9. ARM AND INTERARM STAR FORMATION IN SPIRAL GALAXIES

    SciTech Connect

    Foyle, K.; Rix, H.-W.; Walter, F.; Leroy, A. K.

    2010-12-10

    We investigate the relationship between spiral arms and star formation in the grand-design spirals NGC 5194 and NGC 628 and in the flocculent spiral NGC 6946. Filtered maps of near-IR (3.6 {mu}m) emission allow us to identify 'arm regions' that should correspond to regions of stellar mass density enhancements. The two grand-design spirals show a clear two-armed structure, while NGC 6946 is more complex. We examine these arm and interarm regions, looking at maps that trace recent star formation-far-ultraviolet (GALEX NGS) and 24 {mu}m emission (Spitzer SINGS)-and cold gas-CO (HERACLES) and H I (THINGS). We find the star formation tracers and CO more concentrated in the spiral arms than the stellar 3.6 {mu}m flux. If we define the spiral arms as the 25% highest pixels in the filtered 3.6 {mu}m images, we find that the majority (60%) of star formation tracers occur in the interarm regions; this result persists qualitatively even when considering the potential impact of finite data resolution and diffuse interarm 24 {mu}m emission. Even with a generous definition of the arms (45% highest pixels), interarm regions still contribute at least 30% to the integrated star formation rate (SFR) tracers. We look for evidence that spiral arms trigger star or cloud formation using the ratios of SFR (traced by a combination of FUV and 24 {mu}m emission) to H{sub 2} (traced by CO) and H{sub 2} to H I. Any enhancement of SFR/M(H{sub 2}) in the arm region is very small (less than 10%) and the grand-design spirals show no enhancement compared to the flocculent target. Arm regions do show a weak enhancement in H{sub 2}/H I compared to the interarm regions, but at a fixed gas surface density there is little clear enhancement in the H{sub 2}/H I ratio in the arm regions. Thus, it seems that spiral arms may only act to concentrate the gas to higher densities in the arms.

  10. Can cluster environment modify the dynamical evolution of spiral galaxies?

    NASA Technical Reports Server (NTRS)

    Amram, P.; Balkowski, C.; Cayatte, V.; Marcelin, M.; Sullivan, W. T., III

    1993-01-01

    Over the past decade many effects of the cluster environment on member galaxies have been established. These effects are manifest in the amount and distribution of gas in cluster spirals, the luminosity and light distributions within galaxies, and the segregation of morphological types. All these effects could indicate a specific dynamical evolution for galaxies in clusters. Nevertheless, a more direct evidence, such as a different mass distribution for spiral galaxies in clusters and in the field, is not yet clearly established. Indeed, Rubin, Whitmore, and Ford (1988) and Whitmore, Forbes, and Rubin (1988) (referred to as RWF) presented evidence that inner cluster spirals have falling rotation curves, unlike those of outer cluster spirals or the great majority of field spirals. If falling rotation curves exist in centers of clusters, as argued by RWF, it would suggest that dark matter halos were absent from cluster spirals, either because the halos had become stripped by interactions with other galaxies or with an intracluster medium, or because the halos had never formed in the first place. Even if they didn't disagree with RWF, other researchers pointed out that the behaviour of the slope of the rotation curves of spiral galaxies (in Virgo) is not so clear. Amram, using a different sample of spiral galaxies in clusters, found only 10% of declining rotation curves (2 declining vs 17 flat or rising) in opposition to RWF who find about 40% of declining rotation curves in their sample (6 declining vs 10 flat or rising), we will hereafter briefly discuss the Amram data paper and compare it to the results of RWF. We have measured the rotation curves for a sample of 21 spiral galaxies in 5 nearby clusters. These rotation curves have been constructed from detailed two-dimensional maps of each galaxy's velocity field as traced by emission from the Ha line. This complete mapping, combined with the sensitivity of our CFHT 3.60 m. + Perot-Fabry + CCD observations, allows

  11. Engineering structured light with Vogel spiral arrays of nanoparticles

    NASA Astrophysics Data System (ADS)

    Lawrence, Nate; Trevino, Jacob; Dal Negro, Luca

    2013-03-01

    We present a general analytical model for light scattering by arbitrary Vogel spiral arrays of circular apertures uniformly illuminated at normal incidence. This model suffices to unveil the fundamental mathematical structure of their complex Fraunhofer diffraction patterns and enables the engineering of optical beams carrying multiple values of orbital angular momentum (OAM). By performing analytical Fourier-Hankel decomposition of spiral arrays and far field patterns, we rigorously demonstrate the ability to encode specific numerical sequences onto the OAM values of diffracted optical beams. In particular, we show that these OAM values are determined by the rational approximations of the continued fraction expansions of the irrational angles utilized to generate Vogel spirals. Finally, we experimentally demonstrate structured light carrying multiple values of OAM in the far-field scattering region of Vogel spiral arrays of metallic nanoparticles. Using Fourier-Hankel mode decomposition analysis and interferometric reconstruction of the complex amplitude of scattered waves, we show the ability to encode well-defined numerical sequences, determined by the aperiodic spiral geometry, into azimuthal OAM values, in excellent agreement with analytical scattering theory. The generation of sequences of OAM values by light scattering from engineered aperiodic surfaces is relevant to a number of device applications for secure optical communication, classical and quantum cryptography.

  12. Flow distortion and signal loss in spiral imaging.

    PubMed

    Gatehouse, P D; Firmin, D N

    1999-05-01

    The effect of in-plane motion on the point spread function (velocity PSF) in spiral imaging is studied experimentally and derived mathematically and is shown to consist of a smoothed, trailing edge and fringes around the leading edge. The velocity PSF remains largely in phase with the static PSF, consistent with the absence of signal loss by motion-related phase shifts in central k space. However, single-shot spiral imaging gives no clear improvement in complex and turbulent flow signal uniformity compared with echo-planar imaging with early, central k-space acquisition, which requires explanation given the spiral's earlier coverage of central k space. Alternate leading-edge fringes of the spiral's velocity PSF are in antiphase to the source, and cancellation may occur when these overlap other in-phase signals. Phase variations toward peripheral k space in turbulent flow also cause distortion. It is concluded that spiral imaging may lose complex and turbulent flow signals because of complex PSF distortion. PMID:10332886

  13. Feathering Instability of Spiral Arms. I. Formulation of the Problem

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit; Shu, Frank H.

    2012-09-01

    In this paper, we study the feathering substructures along spiral arms by considering the perturbational gas response to a spiral shock. Feathers are density fluctuations that jut out from the spiral arm to the interarm region at pitch angles given by the quantum numbers of the doubly periodic structure. In a localized asymptotic approximation, related to the shearing sheet except that the inhomogeneities occur in space rather than in time, we derive the linearized perturbation equations for a razor-thin disk with turbulent interstellar gas, frozen-in magnetic field, and gaseous self-gravity. Apart from the modal quantum numbers, the individual normal modes of the system depend on seven dimensionless quantities that characterize the underlying time-independent axisymmetric state plus its steady, nonlinear, two-armed spiral-shock response to a hypothesized background density wave supported by the disk stars of the galaxy. We show that some of these normal modes have positive growth rates. Their overdensity contours in the post-shock region are very reminiscent of observed feathering substructures in full magnetohydrodynamic simulations. The feathering substructures are parasitic instabilities intrinsic to the system; thus, their study not only provides potential diagnostics for important parameters that characterize the interstellar medium of external galaxies, but also yields a deeper understanding of the basic mechanism that drives the formation of the giant molecular clouds and the OB stars that outline observed grand-design spirals.

  14. Electrodynamics of a ring-shaped spiral resonator

    NASA Astrophysics Data System (ADS)

    Maleeva, N.; Fistul, M. V.; Karpov, A.; Zhuravel, A. P.; Averkin, A.; Jung, P.; Ustinov, A. V.

    2014-02-01

    We present analytical, numerical, and experimental investigations of electromagnetic resonant modes of a compact monofilar Archimedean spiral resonator shaped in a ring, with no central part. Planar spiral resonators are interesting as components of metamaterials for their compact deep-subwavelength size. Such resonators couple primarily to the magnetic field component of the incident electromagnetic wave, offering properties suitable for magnetic meta-atoms. Surprisingly, the relative frequencies of the resonant modes follow the sequence of the odd numbers as f1:f2:f3:f4… = 1:3:5:7…, despite the nearly identical boundary conditions for electromagnetic fields at the extremities of the resonator. In order to explain the observed spectrum of resonant modes, we show that the current distribution inside the spiral satisfies a particular Carleman type singular integral equation. By solving this equation, we obtain a set of resonant frequencies. The analytically calculated resonance frequencies and the current distributions are in good agreement with experimental data and the results of numerical simulations. By using low-temperature laser scanning microscopy of a superconducting spiral resonator, we compare the experimentally visualized ac current distributions over the spiral with the calculated ones. Theory and experiment agree well with each other. Our analytical model allows for calculation of a detailed three-dimensional magnetic field structure of the resonators.

  15. Morphologies introduced by bistability in barred-spiral galactic potentials

    NASA Astrophysics Data System (ADS)

    Tsigaridi, L.; Patsis, P. A.

    2015-04-01

    We investigate the orbital dynamics of a barred-spiral model when the system is rotating slowly and corotation is located beyond the end of the spiral arms. In the characteristic of the central family of periodic orbits, we find a `bistable region'. In the response model, we observe a ring surrounding the bar and spiral arms starting tangential to the ring. This is a morphology resembling barred-spiral systems with inner rings. However, the dynamics associated with this structure in the case we study is different from that of a typical bar ending close to corotation. The ring of our model is round, or rather elongated perpendicular to the bar. It is associated with a folding (an `S'-shaped feature) of the characteristic of the central family, which is typical in bistable bifurcations. Along the `S' part of the characteristic, we have a change in the orientation of the periodic orbits from an x1-type to an x2-type morphology. The orbits populated in the response model change rather abruptly their orientation when reaching the lowest energy of the `S'. The spirals of the model follow a standard `precessing ellipses flow' and the orbits building them have energies beyond the `S' region. The bar is structured mainly by sticky orbits from regions around the stability islands of the central family. This leads to the appearance of X features in the bars on the galactic plane. Such a bar morphology appears in the unsharp-masked images of some moderately inclined galaxies.

  16. THE SHEARING H I SPIRAL PATTERN OF NGC 1365

    SciTech Connect

    Speights, Jason C.; Westpfahl, David J.

    2011-07-20

    The Tremaine-Weinberg equations are solved for a pattern speed that is allowed to vary with radius. The solution method transforms an integral equation for the pattern speed to a least-squares problem with well-established procedures for statistical analysis. The method applied to the H I spiral pattern of the barred, grand-design galaxy NGC 1365 produces convincing evidence for a radial dependence in the pattern speed. The pattern speed behaves approximately as 1/r and is very similar to the material speed. There are no clear indications of corotation or Lindblad resonances. Tests show that the results are not selection biased, and that the method is not measuring the material speed. Other methods of solving the Tremaine-Weinberg equations for shearing patterns are found to produce results in agreement with those obtained using the current method. Previous estimates that relied on the assumptions of the density-wave interpretation of spiral structure are inconsistent with the results obtained using the current method. The results are consistent with spiral structure theories that allow for shearing patterns, and contradict fundamental assumptions in the density-wave interpretation that are often used for finding spiral arm pattern speeds. The spiral pattern is winding on a characteristic timescale of {approx}500 Myr.

  17. The gas/dust ratio in spiral galaxies

    NASA Technical Reports Server (NTRS)

    Devereux, Nicholas A.

    1990-01-01

    IRAS data are used here to calculate warm dust masses, which are then compared with the molecular and atomic gas masses for 58 spiral galaxies in order to constrain the fraction and the phase of the interstellar medium in spiral galaxies that contributes to the emission measured by IRAS. The dispersion in the ratio of dust mass to total gas mass is larger than expected on the basis of measurement errors. The dispersion in the ratio of dust mass to inner disk gas mass is less than the dispersion in the ratio of IR to radio emission. The inner gas to warm dust mass ratio for spiral galaxies is 1080 + or - 70, indicating that 80-90 percent of the dust mass in spiral galaxies is radiating at over 100 microns and has a temperature less than about 30 K. However, the bulk of the dust in spiral galaxies is less than about 15 K regardless of the phase of the ISM. Both H I and H2-associated dust contributes to the warm 30 K emission.

  18. On wave dark matter in spiral and barred galaxies

    NASA Astrophysics Data System (ADS)

    Martinez-Medina, Luis A.; Bray, Hubert L.; Matos, Tonatiuh

    2015-12-01

    We recover spiral and barred spiral patterns in disk galaxy simulations with a Wave Dark Matter (WDM) background (also known as Scalar Field Dark Matter (SFDM), Ultra-Light Axion (ULA) dark matter, and Bose-Einstein Condensate (BEC) dark matter). Here we show how the interaction between a baryonic disk and its Dark Matter Halo triggers the formation of spiral structures when the halo is allowed to have a triaxial shape and angular momentum. This is a more realistic picture within the WDM model since a non-spherical rotating halo seems to be more natural. By performing hydrodynamic simulations, along with earlier test particles simulations, we demonstrate another important way in which wave dark matter is consistent with observations. The common existence of bars in these simulations is particularly noteworthy. This may have consequences when trying to obtain information about the dark matter distribution in a galaxy, the mere presence of spiral arms or a bar usually indicates that baryonic matter dominates the central region and therefore observations, like rotation curves, may not tell us what the DM distribution is at the halo center. But here we show that spiral arms and bars can develop in DM dominated galaxies with a central density core without supposing its origin on mechanisms intrinsic to the baryonic matter.

  19. Formation and destruction of clouds and spurs in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Shetty, Rahul; Ostriker, E. C.

    We investigate the formation of clouds and substructure in spiral galaxies using high resolution global MHD simulations, including gas self gravity. Previously, local modeling by Kim and Ostriker (2002) has shown that self gravity and magnetic fields cause the growth of high density clumps in the spiral arms rather rapidly; subsequently, these clumps result in the formation of sheared, feather like structures in the interarms, known as spurs. Recently, Shetty and Ostriker (2006) performed global simulations and found that gas self gravity can cause the growth of sheared features regardless of the strength of the external spiral potential. However, a sufficiently strong spiral potential is required to produce arm clouds, as well as spurs, which are the filamentary structures distinctly associated with the spiral arms, having near-perpendicular intersections with the main dust lane. Here, we use higher resolution modeling to study the detailed properties of the clouds and spurs. We analyze the resulting masses, angular momenta, and magnetic fields of the clouds, and their relation to the background dynamics. We also include a feedback mechanism, representing turbulent forcing via supernovae, to destroy the clouds. We thus assess the role of turbulence on the clump properties. Further, we also follow how subsequent spur morphology evolves under quasi-steady conditions. This research is supported by the National Science Foundation under grant AST-0507315.

  20. Pinion tooth surface generation strategy of spiral bevel gears

    NASA Astrophysics Data System (ADS)

    Liu, Guanglei; Fan, Hongwei

    2012-07-01

    Aviation spiral bevel gears are often generated by spiral generated modified (SGM) roll method. In this style, pinion tooth surface modified generation strategy has an important influence on the meshing and contact performances. For the optimal contact pattern and transmission error function, local synthesis is applied to obtain the machine-tool settings of pinion. For digitized machine, four tooth surface generation styles of pinion are proposed. For every style, tooth contact analysis (TCA) is applied to obtain contact pattern and transmission error function. For the difference between TCA transmission error function and design objective curve, the degree of symmetry and agreement are defined and the corresponding sub-objective functions are established. Linear weighted combination method is applied to get an equivalent objective function to evaluate the shape of transmission error function. The computer programs for the process above are developed to analyze the meshing performances of the four pinion tooth surface generation styles for a pair of aviation spiral bevel gears with 38/43 teeth numbers. The four analytical results are compared with each other and show that the incomplete modified roll is optimal for this gear pair. This study is an expansion to generation strategy of spiral bevel gears, and offers new alternatives to computer numerical control (CNC) manufacture of spiral bevel gears.

  1. Gas and stellar spiral structures in tidally perturbed disc galaxies

    NASA Astrophysics Data System (ADS)

    Pettitt, Alex R.; Tasker, Elizabeth J.; Wadsley, James W.

    2016-06-01

    Tidal interactions between disc galaxies and low-mass companions are an established method for generating galactic spiral features. In this work, we present a study of the structure and dynamics of spiral arms driven in interactions between disc galaxies and perturbing companions in 3D N-body/smoothed hydrodynamical numerical simulations. Our specific aims are to characterize any differences between structures formed in the gas and stars from a purely hydrodynamical and gravitational perspective, and to find a limiting case for spiral structure generation. Through analysis of a number of different interacting cases, we find that there is very little difference between arm morphology, pitch angles and pattern speeds between the two media. The main differences are a minor offset between gas and stellar arms, clear spurring features in gaseous arms, and different radial migration of material in the stronger interacting cases. We investigate the minimum mass of a companion required to drive spiral structure in a galactic disc, finding the limiting spiral generation cases with companion masses of the order of 1 × 109 M⊙, equivalent to only 4 per cent of the stellar disc mass, or 0.5 per cent of the total galactic mass of a Milky Way analogue.

  2. Hot Gaseous Coronae around Spiral Galaxies: Probing the Illustris Simulation

    NASA Astrophysics Data System (ADS)

    Bogdán, Ákos; Vogelsberger, Mark; Kraft, Ralph P.; Hernquist, Lars; Gilfanov, Marat; Torrey, Paul; Churazov, Eugene; Genel, Shy; Forman, William R.; Murray, Stephen S.; Vikhlinin, Alexey; Jones, Christine; Böhringer, Hans

    2015-05-01

    The presence of hot gaseous coronae around present-day massive spiral galaxies is a fundamental prediction of galaxy formation models. However, our observational knowledge remains scarce, since to date only four gaseous coronae have been detected around spirals with massive stellar bodies (≳ 2× {{10}11} {{M}⊙ }). To explore the hot coronae around lower mass spiral galaxies, we utilized Chandra X-ray observations of a sample of eight normal spiral galaxies with stellar masses of (0.7-2.0)× {{10}11} {{M}⊙ }. Although statistically significant diffuse X-ray emission is not detected beyond the optical radii (˜20 kpc) of the galaxies, we derive 3σ limits on the characteristics of the coronae. These limits, complemented with previous detections of NGC 1961 and NGC 6753, are used to probe the Illustris Simulation. The observed 3σ upper limits on the X-ray luminosities and gas masses exceed or are at the upper end of the model predictions. For NGC 1961 and NGC 6753 the observed gas temperatures, metal abundances, and electron density profiles broadly agree with those predicted by Illustris. These results hint that the physics modules of Illustris are broadly consistent with the observed properties of hot coronae around spiral galaxies. However, one shortcoming of Illustris is that massive black holes, mostly residing in giant ellipticals, give rise to powerful radio-mode active galactic nucleus feedback, which results in under-luminous coronae for ellipticals.

  3. Electrodynamics of a ring-shaped spiral resonator

    SciTech Connect

    Maleeva, N.; Karpov, A.; Averkin, A.; Fistul, M. V.; Zhuravel, A. P.; Jung, P.; Ustinov, A. V.

    2014-02-14

    We present analytical, numerical, and experimental investigations of electromagnetic resonant modes of a compact monofilar Archimedean spiral resonator shaped in a ring, with no central part. Planar spiral resonators are interesting as components of metamaterials for their compact deep-subwavelength size. Such resonators couple primarily to the magnetic field component of the incident electromagnetic wave, offering properties suitable for magnetic meta-atoms. Surprisingly, the relative frequencies of the resonant modes follow the sequence of the odd numbers as f{sub 1}:f{sub 2}:f{sub 3}:f{sub 4}… = 1:3:5:7…, despite the nearly identical boundary conditions for electromagnetic fields at the extremities of the resonator. In order to explain the observed spectrum of resonant modes, we show that the current distribution inside the spiral satisfies a particular Carleman type singular integral equation. By solving this equation, we obtain a set of resonant frequencies. The analytically calculated resonance frequencies and the current distributions are in good agreement with experimental data and the results of numerical simulations. By using low-temperature laser scanning microscopy of a superconducting spiral resonator, we compare the experimentally visualized ac current distributions over the spiral with the calculated ones. Theory and experiment agree well with each other. Our analytical model allows for calculation of a detailed three-dimensional magnetic field structure of the resonators.

  4. On galaxy spiral arms' nature as revealed by rotation frequencies

    NASA Astrophysics Data System (ADS)

    Roca-Fàbrega, Santi; Valenzuela, Octavio; Figueras, Francesca; Romero-Gómez, Mercè; Velázquez, Héctor; Antoja, Teresa; Pichardo, Bárbara

    2013-07-01

    High-resolution N-body simulations using different codes and initial condition techniques reveal two different behaviours for the rotation frequency of transient spiral arms like structures. Whereas unbarred discs present spiral arms nearly corotating with disc particles, strong barred models (bulged or bulgeless) quickly develop a bar-spiral structure dominant in density, with a pattern speed almost constant in radius. As the bar strength decreases the arm departs from bar rigid rotation and behaves similar to the unbarred case. In strong barred models, we detect in the frequency space other subdominant and slower modes at large radii, in agreement with previous studies, however, we also detect them in the configuration space. We propose that the distinctive behaviour of the dominant spiral modes can be exploited in order to constraint the nature of Galactic spiral arms by the astrometric survey Gaia and by 2D spectroscopic surveys like Calar Alto Legacy Integral Field Area Survey (CALIFA) and Mapping Nearby Galaxies at APO (MANGA) in external galaxies.

  5. Feathering Instability of Spiral Arms and OB Star Formation

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit; Shu, F. H.

    2012-01-01

    Quasi-regular substructures of the spiral arm are commonly found in spiral galaxies. These substructures are known as feathers or spurs, and they jut out perpendicularly into the inter-arm region. They also associate with the Giant Molecular Clouds where massive star formation occurs. The formation of these density fluctuation can be studied from the perspective of perturbation of galactic spiral shock. We investigate the gas response under the influcence of the shock perturbation, and formulate the MHD equations in a local two-dimensional quasi-rectangular region between tightly-winding spiral arms. Our theoretical model includes the effect of magnetic field and self-gravity of the gas, we are able to reproduce feather-like structures in the post-shock region. In this semi-analytical framework, the periodic density fluctuations depends on the various background parameters such as pattern speed, strength of spiral arm, surface density of the gas and strength of magnetic field. Potentially this study can help understand the inter-arm environment that will be observed in the nearby galaxies using submillimeter telescope such ALMA in the coming years.

  6. Assessments of Coronary Artery Visibility and Radiation Dose in Infants with Congenital Heart Disease on Cardiac 128-slice CT and on Cardiac 64-slice CT.

    PubMed

    Cui, Y; Huang, M; Zheng, J; Li, J; Liu, H; Liang, C

    2016-01-01

    The aim of this study was to compare the coronary artery visibility and radiation dose in infants with CHD on cardiac 128-slice CT and on cardiac 64-slice CT. The images of 200 patients were analyzed in this study, 100 patients were selected randomly from a group of 789 infants (<1 years old) with CHD undergoing 128-slice CT prospective ECG-triggered axial scan, and 100 were selected randomly from 911 infants with CHD undergoing 64-slice CT retrospective ECG-gated spiral scan. The visibility of coronary artery segments was graded on a four-point scale. The coronary arteries were considered to be detected or visible when grade was 2 or higher. The visibility of the coronary artery segments and the radiation dose was compared between the two groups. Except for the rate of LM (96 vs. 99%), the detection rates of the total, LAD, LCX, RCA, and the proximal segment of the RCA in the 256-slice CT group were significantly higher than those in the 64-slice CT group (51.7, 53.33, 33.67, 53.33, and 99 vs. 34.8, 34.33, 18, 30.67, and 75%, respectively). The counts of visibility score (4/3/2/1) for the LM and the proximal segment of the RCA were 62/22/12/4 and 56/20/17/7, respectively, in the 128-slice CT group and 17/42/30/1 and 9/30/38/25, respectively, in the 64-slice CT group. There were significant differences, especially for score 4 and 3, between the two groups. The radiation dose in the 128-slice CT group was significantly decreased than those in the 64-slice CT group (CTDIvol 1.88 ± 0.51 vs. 5.61 ± 0.63 mGy; SSDE 4.48 ± 1.15 vs. 13.97 ± 1.52 mGy; effective radiation dose 1.36 ± 0.44 vs. 4.06 ± 0.7 mSv). With reduced radiation dose, the visibility of the coronary artery in infants with CHD via prospective ECG-triggered mode on a 128-slice CT is superior to that of the 64-slice CT using retrospective ECG-gated spiral mode. PMID:26271472

  7. A Grazing Encounter Between Two Spiral Galaxies

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The larger and more massive galaxy is cataloged as NGC 2207 (on the left in the Hubble Heritage image), and the smaller one on the right is IC 2163. Strong tidal forces from NGC 2207 have distorted the shape of IC 2163, flinging out stars and gas into long streamers stretching out a hundred thousand light-years toward the right-hand edge of the image. Computer simulations, carried out by a team led by Bruce and Debra Elmegreen, demonstrate the leisurely timescale over which galactic collisions occur. In addition to the Hubble images, measurements made with the National Science Foundation's Very Large Array Radio Telescope in New Mexico reveal the motions of the galaxies and aid the reconstruction of the collision. The calculations indicate that IC 2163 is swinging past NGC 2207 in a counterclockwise direction, having made its closest approach 40 million years ago. However, IC 2163 does not have sufficient energy to escape from the gravitational pull of NGC 2207, and is destined to be pulled back and swing past the larger galaxy again in the future. The high resolution of the Hubble telescope image reveals dust lanes in the spiral arms of NGC 2207, clearly silhouetted against IC 2163, which is in the background. Hubble also reveals a series of parallel dust filaments extending like fine brush strokes along the tidally stretched material on the right-hand side. The large concentrations of gas and dust in both galaxies may well erupt into regions of active star formation in the near future. Trapped in their mutual orbit around each other, these two galaxies will continue to distort and disrupt each other. Eventually, billions of years from now, they will merge into a single, more massive galaxy. It is believed that many present-day galaxies, including the Milky Way, were assembled from a similar process of coalescence of smaller galaxies occurring over billions of years. This image was created from 3 separate pointings of Hubble. The Wide Field Planetary Camera 2 data

  8. Characterization of Atmospheric Ekman Spirals at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Rysman, Jean-François; Lahellec, Alain; Vignon, Etienne; Genthon, Christophe; Verrier, Sébastien

    2016-03-01

    We use wind speed and temperature measurements taken along a 45-m meteorological tower located at Dome C, Antarctica (75.06° S, 123.19° E) to highlight and characterize the Ekman spiral. Firstly, temperature records reveal that the atmospheric boundary layer at Dome C is stable during winter and summer nights (i.e., > 85 % of the time). The wind vector, in both speed and direction, also shows a strong dependence with elevation. An Ekman model was then fitted to the measurements. Results show that the wind vector follows the Ekman spiral structure for more than 20 % of the year (2009). Most Ekman spirals have been detected during summer nights, that is, when the boundary layer is slightly stratified. During these episodes, the boundary-layer height ranged from 25 to 100 m, the eddy viscosity from 0.004 to 0.06 m^2 s^{-1} , and the Richardson number from zero to 1.6.

  9. Spiral Bevel Gear Damage Detection Using Decision Fusion Analysis

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Handschuh, Robert F.; Afjeh, Abdollah A.

    2002-01-01

    A diagnostic tool for detecting damage to spiral bevel gears was developed. Two different monitoring technologies, oil debris analysis and vibration, were integrated using data fusion into a health monitoring system for detecting surface fatigue pitting damage on gears. This integrated system showed improved detection and decision-making capabilities as compared to using individual monitoring technologies. This diagnostic tool was evaluated by collecting vibration and oil debris data from fatigue tests performed in the NASA Glenn Spiral Bevel Gear Fatigue Rigs. Data was collected during experiments performed in this test rig when pitting damage occurred. Results show that combining the vibration and oil debris measurement technologies improves the detection of pitting damage on spiral bevel gears.

  10. Directly observing continuum emission from self-gravitating spiral waves

    NASA Astrophysics Data System (ADS)

    Hall, Cassandra; Forgan, Duncan; Rice, Ken; Harries, Tim J.; Klaassen, Pamela D.; Biller, Beth

    2016-05-01

    We use a simple, self-consistent, self-gravitating semi-analytic disc model to conduct an examination of the parameter space in which self-gravitating discs may exist. We then use Monte Carlo radiative transfer to generate synthetic Atacama Large Millimeter/submillimeter Array (ALMA) images of these self-gravitating discs to determine the subset of this parameter space in which they generate non-axisymmetric structure that is potentially detectable by ALMA. Recently, several transition discs have been observed to have non-axisymmetric structure that extends out to large radii. It has been suggested that one possible origin of these asymmetries could be spiral density waves induced by disc self-gravity. We use our simple model to see if these discs exist in the region of parameter space where self-gravity could feasibly explain these spiral features. We find that for self-gravity to play a role in these systems typically requires a disc mass around an order of magnitude higher than the observed disc masses for the systems. The spiral amplitudes produced by self-gravity in the local approximation are relatively weak when compared to amplitudes produced by tidal interactions, or spirals launched at Lindblad resonances due to embedded planets in the disc. As such, we ultimately caution against diagnosing spiral features as being due to self-gravity, unless the disc exists in the very narrow region of parameter space where the spiral wave amplitudes are large enough to produce detectable features, but not so large as to cause the disc to fragment.

  11. The onset of spiral structure in the universe

    SciTech Connect

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.

    2014-01-20

    The onset of spiral structure in galaxies appears to occur between redshifts 1.4 and 1.8 when disks have developed a cool stellar component, rotation dominates over turbulent motions in the gas, and massive clumps become less frequent. During the transition from clumpy to spiral disks, two unusual types of spirals are found in the Hubble Ultra Deep Field that are massive, clumpy, and irregular like their predecessor clumpy disks, yet spiral-like or sheared like their descendants. One type is 'woolly' with massive clumpy arms all over the disk and is brighter than other disk galaxies at the same redshift, while another type has irregular multiple arms with high pitch angles, star formation knots, and no inner symmetry like today's multiple-arm galaxies. The common types of spirals seen locally are also present in a redshift range around z ∼ 1, namely grand design with two symmetric arms, multiple arm with symmetry in the inner parts and several long, thin arms in the outer parts, and flocculent, with short, irregular, and patchy arms that are mostly from star formation. Normal multiple-arm galaxies are found only closer than z ∼ 0.6 in the Ultra Deep Field. Grand design galaxies extend furthest to z ∼ 1.8, presumably because interactions can drive a two-arm spiral in a disk that would otherwise have a more irregular structure. The difference between these types is understandable in terms of the usual stability parameters for gas and stars, and the ratio of the velocity dispersion to rotation speed.

  12. TH-C-18A-11: Investigating the Minimum Scan Parameters Required to Generate Free-Breathing Fast-Helical CT Scans Without Motion-Artifacts

    SciTech Connect

    Thomas, D; Neylon, J; Dou, T; Jani, S; Lamb, J; Low, D; Tan, J

    2014-06-15

    Purpose: A recently proposed 4D-CT protocol uses deformable registration of free-breathing fast-helical CT scans to generate a breathing motion model. In order to allow accurate registration, free-breathing images are required to be free of doubling-artifacts, which arise when tissue motion is greater than scan speed. This work identifies the minimum scanner parameters required to successfully generate free-breathing fast-helical scans without doubling-artifacts. Methods: 10 patients were imaged under free breathing conditions 25 times in alternating directions with a 64-slice CT scanner using a low dose fast helical protocol. A high temporal resolution (0.1s) 4D-CT was generated using a patient specific motion model and patient breathing waveforms, and used as the input for a scanner simulation. Forward projections were calculated using helical cone-beam geometry (800 projections per rotation) and a GPU accelerated reconstruction algorithm was implemented. Various CT scanner detector widths and rotation times were simulated, and verified using a motion phantom. Doubling-artifacts were quantified in patient images using structural similarity maps to determine the similarity between axial slices. Results: Increasing amounts of doubling-artifacts were observed with increasing rotation times > 0.2s for 16×1mm slice scan geometry. No significant increase in doubling artifacts was observed for 64×1mm slice scan geometry up to 1.0s rotation time although blurring artifacts were observed >0.6s. Using a 16×1mm slice scan geometry, a rotation time of less than 0.3s (53mm/s scan speed) would be required to produce images of similar quality to a 64×1mm slice scan geometry. Conclusion: The current generation of 16 slice CT scanners, which are present in most Radiation Oncology departments, are not capable of generating free-breathing sorting-artifact-free images in the majority of patients. The next generation of CT scanners should be capable of at least 53mm/s scan speed

  13. CT of Gastric Emergencies.

    PubMed

    Guniganti, Preethi; Bradenham, Courtney H; Raptis, Constantine; Menias, Christine O; Mellnick, Vincent M

    2015-01-01

    Abdominal pain, nausea, and vomiting are common presenting symptoms among adult patients seeking care in the emergency department, and, with the increased use of computed tomography (CT) to image patients with these complaints, radiologists will more frequently encounter a variety of emergent gastric pathologic conditions on CT studies. Familiarity with the CT appearance of emergent gastric conditions is important, as the clinical presentation is often nonspecific and the radiologist may be the first to recognize gastric disease as the cause of a patient's symptoms. Although endoscopy and barium fluoroscopy remain important tools for evaluating patients with suspected gastric disease in the outpatient setting, compared with CT these modalities enable less comprehensive evaluation of patients with nonspecific complaints and are less readily available in the acute setting. Endoscopy is also more invasive than CT and has greater potential risks. Although the mucosal detail of CT is relatively poor compared with barium fluoroscopy or endoscopy, CT can be used with the appropriate imaging protocols to identify inflammatory conditions of the stomach ranging from gastritis to peptic ulcer disease. In addition, CT can readily demonstrate the various complications of gastric disease, including perforation, obstruction, and hemorrhage, which may direct further clinical, endoscopic, or surgical management. We will review the normal anatomy of the stomach and discuss emergent gastric disease with a focus on the usual clinical presentation, typical imaging appearance, and differentiating features, as well as potential imaging pitfalls. PMID:26562229

  14. Clinical evaluation of a commercial orthopedic metal artifact reduction tool for CT simulations in radiation therapy

    SciTech Connect

    Li Hua; Noel, Camille; Chen, Haijian; Harold Li, H.; Low, Daniel; Moore, Kevin; Klahr, Paul; Michalski, Jeff; Gay, Hiram A.; Thorstad, Wade; Mutic, Sasa

    2012-12-15

    Purpose: Severe artifacts in kilovoltage-CT simulation images caused by large metallic implants can significantly degrade the conspicuity and apparent CT Hounsfield number of targets and anatomic structures, jeopardize the confidence of anatomical segmentation, and introduce inaccuracies into the radiation therapy treatment planning process. This study evaluated the performance of the first commercial orthopedic metal artifact reduction function (O-MAR) for radiation therapy, and investigated its clinical applications in treatment planning. Methods: Both phantom and clinical data were used for the evaluation. The CIRS electron density phantom with known physical (and electron) density plugs and removable titanium implants was scanned on a Philips Brilliance Big Bore 16-slice CT simulator. The CT Hounsfield numbers of density plugs on both uncorrected and O-MAR corrected images were compared. Treatment planning accuracy was evaluated by comparing simulated dose distributions computed using the true density images, uncorrected images, and O-MAR corrected images. Ten CT image sets of patients with large hip implants were processed with the O-MAR function and evaluated by two radiation oncologists using a five-point score for overall image quality, anatomical conspicuity, and CT Hounsfield number accuracy. By utilizing the same structure contours delineated from the O-MAR corrected images, clinical IMRT treatment plans for five patients were computed on the uncorrected and O-MAR corrected images, respectively, and compared. Results: Results of the phantom study indicated that CT Hounsfield number accuracy and noise were improved on the O-MAR corrected images, especially for images with bilateral metal implants. The {gamma} pass rates of the simulated dose distributions computed on the uncorrected and O-MAR corrected images referenced to those of the true densities were higher than 99.9% (even when using 1% and 3 mm distance-to-agreement criterion), suggesting that dose

  15. Clinical evaluation of a commercial orthopedic metal artifact reduction tool for CT simulations in radiation therapy

    PubMed Central

    Li, Hua; Noel, Camille; Chen, Haijian; Harold Li, H.; Low, Daniel; Moore, Kevin; Klahr, Paul; Michalski, Jeff; Gay, Hiram A.; Thorstad, Wade; Mutic, Sasa

    2012-01-01

    Purpose: Severe artifacts in kilovoltage-CT simulation images caused by large metallic implants can significantly degrade the conspicuity and apparent CT Hounsfield number of targets and anatomic structures, jeopardize the confidence of anatomical segmentation, and introduce inaccuracies into the radiation therapy treatment planning process. This study evaluated the performance of the first commercial orthopedic metal artifact reduction function (O-MAR) for radiation therapy, and investigated its clinical applications in treatment planning. Methods: Both phantom and clinical data were used for the evaluation. The CIRS electron density phantom with known physical (and electron) density plugs and removable titanium implants was scanned on a Philips Brilliance Big Bore 16-slice CT simulator. The CT Hounsfield numbers of density plugs on both uncorrected and O-MAR corrected images were compared. Treatment planning accuracy was evaluated by comparing simulated dose distributions computed using the true density images, uncorrected images, and O-MAR corrected images. Ten CT image sets of patients with large hip implants were processed with the O-MAR function and evaluated by two radiation oncologists using a five-point score for overall image quality, anatomical conspicuity, and CT Hounsfield number accuracy. By utilizing the same structure contours delineated from the O-MAR corrected images, clinical IMRT treatment plans for five patients were computed on the uncorrected and O-MAR corrected images, respectively, and compared. Results: Results of the phantom study indicated that CT Hounsfield number accuracy and noise were improved on the O-MAR corrected images, especially for images with bilateral metal implants. The γ pass rates of the simulated dose distributions computed on the uncorrected and O-MAR corrected images referenced to those of the true densities were higher than 99.9% (even when using 1% and 3 mm distance-to-agreement criterion), suggesting that dose

  16. Spiral waves and instability in magnetized astrophysical disks

    SciTech Connect

    Tagger, M.; Henriksen, R.N.; Sygnet, J.F.; Pellat, R. CNRS, Institut d'Astrophysique, Paris Ecole Polytechnique, Palaiseau )

    1990-04-01

    It is shown that an ionized disk in a vertical magnetic field (e.g., the dipole field of the central object for an accretion or planetary disk) is subject to spiral instabilities of low azimuthal wavenumber, driven by differential rotation. The amplification is due to the Swing mechanism already known for the spiral instability of galactic disks, with self-gravity replaced by magnetic forces. In realistic cases the growth time is a few tens of rotation periods. Such instabilities, or waves driven by irregularities in the ambient magnetic field, might be important in particular for accretion disks, and to explain the spokes in Saturn's rings. 11 refs.

  17. Spiral Orbit Tribometry I: Description of the Tribometer

    NASA Technical Reports Server (NTRS)

    Pepper, Stephen V.; Kingsbury, Edward P.; Kiraly, Louis J. (Technical Monitor)

    2002-01-01

    A new rolling contact tribometer based on a planar thrust bearing geometry is described. The bearing 'races' are flat plates that drive a ball into a near-circular, spiral path. The spiraling ball is returned to its initial radius each revolution around the race by a 'guide plate' backed by a force transducer. The motions of the ball are analyzed and the force exerted by the ball on the guide plate is related to the friction coefficient of the system. The experimental characteristics of the system are presented and the system is shown to exhibit the behavior expected for a tribometer.

  18. Figuring technology of nonaxisymmetric errors with a spiral path.

    PubMed

    Jiao, Changjun; Li, Shengyi; Xie, Xuhui

    2009-08-01

    Figuring technology of nonaxisymmetric errors using a spiral path is presented. Based on an approximation of a removal function, a finite-field nonlinear model is deduced from the computer-controlled optics shaping principle. We then present a modified Richardson-Lucy iterative algorithm to deconvolute the dwell time. With a velocity realization method for dwell time on a spiral path, the figuring technology comes into being. Simulations are made to validate these algorithms. Theoretical and simulation studies demonstrate that the figuring technology is a novel method for inexpensive fabrication of precision mirrors. PMID:19649028

  19. A generalisation of the Pythagorean hodograph quintic spiral

    NASA Astrophysics Data System (ADS)

    Walton, D. J.; Meek, D. S.

    2004-12-01

    An existing planar Pythagorean hodograph (PH) quintic spiral, with zero curvature at one end, is generalised to form a two parameter family of PH quintic spirals. The additional degree of freedom allows specification of an ending angle of tangent and curvature. Its shape and curvature compares well to that of the clothoid which has applications in areas such as highway design and robot path planning. It is thus a viable nonuniform rational B-spline alternative for such applications. It is also useful for other computer aided design or computer-aided geometric design applications in which drawing curves with controlled curvature, e.g. fair curves, is important.

  20. Self-catalyzed anisotropic growth of GaN spirals

    NASA Astrophysics Data System (ADS)

    Patsha, Avinash; Sahoo, Prasana; Dhara, S.; Tyagi, A. K.

    2012-06-01

    GaN spirals with homogeneous size are grown using chemical-vapor-deposition technique in a self catalytic process. Raman and photoluminescence (PL) studies reveal wurtzite GaN phase. Nucleation of GaN sphere takes place with the agglomeration Ga clusters and simultaneous reaction with NH3. A growth mechanism involving diffusion limited aggregation process initiating supersaturation and subsequent neck formation along with possible role of thermodynamic fluctuation in different crystalline facets of GaN, is described for the anisotropic spiral structures. Temperature dependent PL spectra show strong excitonic emissions along with the presence of free-to-bound transition.

  1. Photometric scaling relations of lenticular and spiral galaxies

    NASA Astrophysics Data System (ADS)

    Laurikainen, E.; Salo, H.; Buta, R.; Knapen, J. H.; Comerón, S.

    2010-06-01

    Photometric scaling relations are studied for S0 galaxies and compared with those obtained for spirals. New two-dimensional multi-component decompositions are presented for 122 early-type disc galaxies, using deep Ks-band images. Combining them with our previous decompositions, the final sample consists of 175 galaxies (Near-Infrared Survey of S0s, NIRS0S: 117 S0s + 22 S0/a and 36 Sa galaxies). As a comparison sample we use the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) of nearly 200 spirals, for which similar multi-component decompositions have previously been made by us. The improved statistics, deep images and the homogeneous decomposition method used allow us to re-evaluate the parameters of the bulges and discs. For spirals we largely confirm previous results, which are compared with those obtained for S0s. Our main results are as follows. (1) Important scaling relations are present, indicating that the formative processes of bulges and discs in S0s are coupled [e.g. M0K(disc) = 0.63 M0K(bulge) -9.3], as has been found previously for spirals [for OSUBSGS spirals M0K (disc) = 0.38 M0K(bulge) -15.5 the rms deviation from these relations is 0.5 mag for S0s and spirals]. (2) We obtain median reff/h0r ~ 0.20, 0.15 and 0.10 for S0, S0/a-Sa and Sab-Sc galaxies, respectively: these values are smaller than predicted by simulation models in which bulges are formed by galaxy mergers. (3) The properties of bulges of S0s are different from the elliptical galaxies, which are manifested in the versus reff relation, in the photometric plane (μ0, n, reff), and to some extent also in the Kormendy relation (< μ >eff versus reff). The bulges of S0s are similar to bulges of spirals with M0K(bulge) < -20 mag. Some S0s have small bulges, but their properties are not compatible with the idea that they could evolve to dwarfs by galaxy harassment. (4) The relative bulge flux (B/T) for S0s covers the full range found in the Hubble sequence, even with 13 per cent

  2. Short-term dynamical evolution of grand-design spirals in barred galaxies

    NASA Astrophysics Data System (ADS)

    Baba, Junichi

    2015-12-01

    We investigate the short-term dynamical evolution of stellar grand-design spiral arms in barred spiral galaxiesusing a three-dimensional (3D) N-body/hydrodynamic simulation. Similar to previous numerical simulations of unbarred, multiple-arm spirals, we find that grand-design spiral arms in barred galaxies are not stationary, but rather dynamic. This means that the amplitudes, pitch angles, and rotational frequencies of the spiral arms are not constant, but change within a few hundred million years (i.e. the typical rotational period of a galaxy). We also find that the clear grand-design spirals in barred galaxies appear only when the spirals connect with the ends of the bar. Furthermore, we find that the short-term behaviour of spiral arms in the outer regions (R > 1.5-2 bar radius) can be explained by the swing amplification theory and that the effects of the bar are not negligible in the inner regions (R < 1.5-2 bar radius). These results suggest that although grand-design spiral arms in barred galaxies are affected by the stellar bar, the grand-design spiral arms essentially originate not as bar-driven stationary density waves, but rather as self-excited dynamic patterns. We imply that a rigidly rotating grand-design spiral could not be a reasonable dynamical model for investigating gas flows and cloud formation even in barred spiral galaxies.

  3. 21 CFR 884.2675 - Fetal scalp circular (spiral) electrode and applicator.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Fetal scalp circular (spiral) electrode and... Gynecological Monitoring Devices § 884.2675 Fetal scalp circular (spiral) electrode and applicator. (a) Identification. A fetal scalp circular (spiral) electrode and applicator is a device used to obtain a...

  4. 21 CFR 884.2675 - Fetal scalp circular (spiral) electrode and applicator.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Fetal scalp circular (spiral) electrode and... Gynecological Monitoring Devices § 884.2675 Fetal scalp circular (spiral) electrode and applicator. (a) Identification. A fetal scalp circular (spiral) electrode and applicator is a device used to obtain a...

  5. A Spiral Task as a Model for In-Service Teacher Education

    ERIC Educational Resources Information Center

    Fried, Michael N.; Amit, Miriam

    2005-01-01

    The spiral approach has long been used by curriculum designers to deepen students' knowledge of scientific and mathematical concepts and to bring students to higher levels of abstraction. The benefits of a spiral approach, however, can also be extended to teacher education. This paper describes a spiral activity employed by the "Kidumatica"…

  6. The beam quality parameter of spirally polarized beams

    NASA Astrophysics Data System (ADS)

    Ramírez-Sánchez, V.; Piquero, G.

    2008-12-01

    Starting from the expression for the quality parameter of a superposition of two general fields, the case of beams that can be written in terms of the polarization basis introduced by Gori is investigated. Different types of this class of beam are studied and compared. In particular, spirally polarized beams are considered. As an example, polarized Bessel-Gauss beams are analyzed in detail.

  7. Crowds as an Excitable Medium for Spiral Wave Dynamics

    NASA Astrophysics Data System (ADS)

    Welsh, Andrea; Greco, Edwin; Fenton, Flavio

    Spiral wave (SW) patterns are studied in many physical, biological, and chemical excitable systems. Of particular importance are SW of electrical activity that develop in the heart and give rise to arrhythmias such as tachycardia (single SW) and fibrillation (multiple SWs). We investigate if a crowd of people given simple rules for activation and deactivation, modeled on cardiac cells, can act as a living simulation for SW dynamics. For group sizes ranging from 50 to 650 people we demonstrate, experimentally, the existence of stable spiral waves and of spiral wave breakup leading to chaotic dynamics. Numerical simulation predicts the simple rules lead to well define wave fronts. People, however, respond with various degrees of anticipation and misinformation. This human behavior can lead to smoothed fronts or even lead to spiral wave breakup and chaos. We present a new cell model that includes variations in reaction to account for the observed behavior in crowds. This model may be useful in the study of coupling and decoupling of cardiac cells that lead to arrhythmic behavior. Supported by NSF.

  8. Rugose Spiraling Whitefly: A new invasive pest in Florida

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aleurodicus rugioperculatus Martin, commonly known as gumbo limbo or rugose spiraling whitefly is a new addition in the list of devastating whitefly species found in Florida. Because it is a fairly new species to science (identified less than a decade ago) not much information is available about thi...

  9. A Parallax-based Distance Estimator for Spiral Arm Sources

    NASA Astrophysics Data System (ADS)

    Reid, M. J.; Dame, T. M.; Menten, K. M.; Brunthaler, A.

    2016-06-01

    The spiral arms of the Milky Way are being accurately located for the first time via trigonometric parallaxes of massive star-forming regions with the Bar and Spiral Structure Legacy Survey, using the Very Long Baseline Array and the European VLBI Network, and with the Japanese VLBI Exploration of Radio Astrometry project. Here we describe a computer program that leverages these results to significantly improve the accuracy and reliability of distance estimates to other sources that are known to follow spiral structure. Using a Bayesian approach, sources are assigned to arms based on their (l, b, v) coordinates with respect to arm signatures seen in CO and H i surveys. A source's kinematic distance, displacement from the plane, and proximity to individual parallax sources are also considered in generating a full distance probability density function. Using this program to estimate distances to large numbers of star-forming regions, we generate a realistic visualization of the Milky Way's spiral structure as seen from the northern hemisphere.

  10. On stability and spiral patterns in polar disks

    NASA Astrophysics Data System (ADS)

    Theis, Ch.; Sparke, L.; Gallagher, J.

    2006-02-01

    To investigate the stability properties of polar disks we performed two-dimensional hydrodynamical simulations for flat polytropic gaseous self-gravitating disks which were perturbed by a central S0-like component. Our disk was constructed to resemble that of the proto-typical galaxy NGC 4650A. This central perturbation induces initially a stationary two-armed tightly-wound leading spiral in the polar disk. For a hot disk (Toomre parameter Q>1.7), the structure does not change over the simulation time of 4.5 Gyr. In case of colder disks, the self-gravity of the spiral becomes dominant, it decouples from the central perturbation and grows, until reaching a saturation stage in which an open trailing spiral is formed, rather similar to that observed in NGC 4650A. The timescale for developing non-linear structures is 1-2 Gyr; saturation is reached within 2-3 Gyr. The main parameter controlling the structure formation is the Toomre parameter. The results are surprisingly insensitive to the properties of the central component. If the polar disk is much less massive than that in NGC 4650A, it forms a weaker tightly-wound spiral, similar to that seen in dust absorption in the dust disk of NGC 2787. Our results are derived for a polytropic equation of state, but appear to be generic as the adiabatic exponent is varied between γ = 1 (isothermal) and γ = 2 (very stiff).

  11. 61. View of TR spiral access stair system from transmitter ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    61. View of TR spiral access stair system from transmitter building no. 102 mezzanine level; note elevator door on right. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

  12. METHODS FOR THE SPIRAL SALMONELLA MUTAGENICITY ASSAY INCLUDING SPECIALIZED APPLICATIONS

    EPA Science Inventory

    ABSTRACT

    An automated approach to bacterial mutagenicity testing--the spiral Salmonella assay--was developed to simplify testing and to reduce the labor and materials required to generate dose-responsive mutagenicity information. This document provides the reader with an ...

  13. Dynamical effect of gas on spiral pattern speed in galaxies

    NASA Astrophysics Data System (ADS)

    Ghosh, Soumavo; Jog, Chanda J.

    2016-07-01

    In the density wave theory of spiral structure, the grand-design two-armed spiral pattern is taken to rotate rigidly in a galactic disc with a constant, definite pattern speed. The observational measurement of the pattern speed of the spiral arms, though difficult, has been achieved in a few galaxies such as NGC 6946, NGC 2997, and M 51 which we consider here. We examine whether the theoretical dispersion relation permits a real solution for wavenumber corresponding to a stable wave, for the observed rotation curve and the pattern speed values. We find that the disc when modelled as a stars-alone case, as is usually done in literature, does not generally give a stable density wave solution for the observed pattern speed. Instead the inclusion of the low velocity dispersion component, namely, gas, is essential to obtain a stable density wave. Further, we obtain a theoretical range of allowed pattern speeds that correspond to a stable density wave at a certain radius, and check that for the three galaxies considered, the observed pattern speeds fall in the respective prescribed range. The inclusion of even a small amount (˜15 per cent) of gas by mass fraction in the galactic disc is shown to have a significant dynamical effect on the dispersion relation and hence on the pattern speed that is likely to be seen in a real, gas-rich spiral galaxy.

  14. Enhanced Abundances in Spiral Galaxies of the Pegasus I Cluster

    NASA Astrophysics Data System (ADS)

    Robertson, Paul; Shields, Gregory A.; Blanc, Guillermo A.

    2012-03-01

    We study the influence of cluster environment on the chemical evolution of spiral galaxies in the Pegasus I cluster. We determine the gas-phase heavy element abundances of six galaxies in Pegasus derived from H II region spectra obtained from integral-field spectroscopy. These abundances are analyzed in the context of Virgo, whose spirals are known to show increasing interstellar metallicity as a function of H I deficiency. The galaxies in the Pegasus cluster, despite its lower density and velocity dispersion, also display gas loss due to interstellar-medium-intracluster-medium interaction, albeit to a lesser degree. Based on the abundances of three H I deficient spirals and two H I normal spirals, we observe a heavy element abundance offset of +0.13 ± 0.07 dex for the H I deficient galaxies. This abundance differential is consistent with the differential observed in Virgo for galaxies with a similar H I deficiency, and we observe a correlation between log (O/H) and the H I deficiency parameter DEF for the two clusters analyzed together. Our results suggest that similar environmental mechanisms are driving the heavy element enhancement in both clusters.

  15. Geometrical analysis of circular-cut spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Huston, R. L.

    1983-01-01

    Geometrical studies of circular cut spiral bevel gears are reported. Tooth profile changes heel to toe are studied in the transverse plane. Pressure angle changes are determined. The radiuses of curvature of the tooth surfaces generated by various cutter profiles are also determined. The consequences of cutter profile changes are explored. Crown gears are emphasized and the implications for conical gears are discussed.

  16. 4. NORTH END OF TERMINAL ROOM, SHOP LEVEL SHOWING SPIRAL ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. NORTH END OF TERMINAL ROOM, SHOP LEVEL SHOWING SPIRAL STAIR TO CABLE RACK. Looking north. - Edwards Air Force Base, Air Force Rocket Propulsion Laboratory, Test Stand 1-A Terminal Room, Test Area 1-120, north end of Jupiter Boulevard, Boron, Kern County, CA

  17. SPIRAL (Sandia's Program for Information Retrieval and Listing)

    ERIC Educational Resources Information Center

    West, Leslie E.

    The general scope of SPIRAL is storage of free-flowing text information into a machine-readable library and recall of any portions of this stored information that are relevant to an inquiry. The major objectives in the design of the system were (1) to make it easy to use by persons unfamiliar with computer systems; and (2) to make it efficient, in…

  18. The Cognitive Spiral: Creative Thinking and Cognitive Processing.

    ERIC Educational Resources Information Center

    Ebert, Edward S., II

    1994-01-01

    The lack of a common understanding of the construct of creative thinking is noted, and the cognitive spiral model is presented, which conceptualizes creative thinking as an integral component of all cognitive processing. This article details the synthesis of a definition and the structure of a model of cognitive processing. (Author/DB)

  19. Deceptively Simple Harmonic Motion: A Mass on a Spiral Spring.

    ERIC Educational Resources Information Center

    McDonald, F. Alan

    1980-01-01

    Discusses the oscillatory motion of a mass on a spiral (nonhelical) spring, and calculates the lowest eigenfrequency and the associated effective spring mass for a range of values of the attached mass. Analytic and numerical comparisons are made to the helical spring problem. (HM)

  20. ENHANCED ABUNDANCES IN SPIRAL GALAXIES OF THE PEGASUS I CLUSTER

    SciTech Connect

    Robertson, Paul; Shields, Gregory A.; Blanc, Guillermo A. E-mail: shields@astro.as.utexas.edu

    2012-03-20

    We study the influence of cluster environment on the chemical evolution of spiral galaxies in the Pegasus I cluster. We determine the gas-phase heavy element abundances of six galaxies in Pegasus derived from H II region spectra obtained from integral-field spectroscopy. These abundances are analyzed in the context of Virgo, whose spirals are known to show increasing interstellar metallicity as a function of H I deficiency. The galaxies in the Pegasus cluster, despite its lower density and velocity dispersion, also display gas loss due to interstellar-medium-intracluster-medium interaction, albeit to a lesser degree. Based on the abundances of three H I deficient spirals and two H I normal spirals, we observe a heavy element abundance offset of +0.13 {+-} 0.07 dex for the H I deficient galaxies. This abundance differential is consistent with the differential observed in Virgo for galaxies with a similar H I deficiency, and we observe a correlation between log (O/H) and the H I deficiency parameter DEF for the two clusters analyzed together. Our results suggest that similar environmental mechanisms are driving the heavy element enhancement in both clusters.

  1. Fingerprints of nucleosynthesis in the local spiral arm

    NASA Technical Reports Server (NTRS)

    Knoedlseder, J.; Bennett, K.; Bloemen, H.; Diehl, R.; Hermsen, W.; Oberlack, U.; Ryan, J.; Schoenfelder, V.; vonBallmoos, P.

    1997-01-01

    The local spiral arm with its inherent massive star population is a natural site of recent nucleosynthesis activity. The features found in 1.8 MeV observation of candidate Al-26 sources situated in this structure are discussed. The emphasis is on Loop 1, a nearby superbubble which is possibly the site of a recent supernova explosion.

  2. Spiral magnets with Dzyaloshinskii-Moriya interaction containing defect bonds

    NASA Astrophysics Data System (ADS)

    Utesov, O. I.; Sizanov, A. V.; Syromyatnikov, A. V.

    2015-09-01

    We present a theory describing spiral magnets with Dzyaloshinskii-Moriya interaction (DMI) subject to bond disorder at small concentration c of defects. It is assumed that both DMI and exchange coupling are changed on imperfect bonds. Qualitatively the same physical picture is obtained in two models which are considered in detail: B20 cubic helimagnets and layered magnets in which DMI leads to a long-period spiral ordering perpendicular to layers. We find that the distortion of the spiral magnetic ordering around a single imperfect bond is long range: values of additional turns of spins decay with the distance r to the defect as 1 /r2 being governed by the Poisson's equation for electric dipole. At finite concentration of randomly distributed imperfect bonds, we calculate correction to the spiral vector. We show that this correction can change the sign of spin chirality even at c ≪1 if defects are strong enough. It is demonstrated that impurities lead to a diffuse elastic neutron scattering which has power-law singularities at magnetic Bragg peaks positions. Then, each Bragg peak acquires power-law decaying tails. Corrections are calculated to the magnon energy and to its damping caused by scattering on impurities.

  3. Electrokinetic particle separation in a single-spiral microchannel

    NASA Astrophysics Data System (ADS)

    DuBose, John; Zhu, Junjie; Patel, Saurin; Lu, Xinyu; Tupper, Nathaniel; Stonaker, John M.; Xuan, Xiangchun

    2014-11-01

    The efficient separation of discrete particle species is a topic of interest in numerous research fields for its practical application to problems encountered in both academia and industry. We have recently developed an electrokinetic technique that exploits the curvature-induced dielectrophoresis (C-iDEP) to continuously sort particles by inherent properties in asymmetric double-spiral microchannels. Herein we demonstrate that a single-spiral microchannel is also sufficient for a continuous-flow sheathless electrokinetic particle separation. This method relies on C-iDEP to focus particles to a tight stream and the wall-induced electric lift to manipulate the aligned particles to size-dependent equilibrium positions, both of which happen simultaneously inside the spiral. A theoretical model is developed to understand this size-based separation, which has been implemented for both a binary mixture and a ternary mixture of colloidal particles. The obtained analytical formulae predict with a close agreement both the experimentally measured particle center-wall distance and the necessary electric field for a complete particle focusing in the spiral.

  4. Molecular Distribution in the Spiral Arm of M51

    NASA Astrophysics Data System (ADS)

    Watanabe, Yoshimasa; Sakai, Nami; Sorai, Kazuo; Ueda, Junko; Yamamoto, Satoshi

    2016-03-01

    Molecular line images of 13CO, C18O, CN, CS, CH3OH, and HNCO are obtained toward the spiral arm of M51 at a 7\\prime\\prime × 6\\prime\\prime resolution with the Combined Array for Research in Millimeter-wave Astronomy. Distributions of the molecules averaged over a 300 pc scale are found to be almost similar to one another and to essentially trace the spiral arm. However, the principal component analysis shows a slight difference of distributions among molecular species, particularly for CH3OH and HNCO. These two species do not correlate well with the star formation rate, implying that they are not enhanced by local star formation activities but by galactic-scale phenomena such as spiral shocks. Furthermore, the distributions of HNCO and CH3OH are found to be slightly different, and their origins deserve further investigation. The present results provide us with an important clue for understanding the 300 pc scale chemical composition in the spiral arm and its relation to galactic-scale dynamics.

  5. Learning in 3D Virtual Environments: Collaboration and Knowledge Spirals

    ERIC Educational Resources Information Center

    Burton, Brian G.; Martin, Barbara N.

    2010-01-01

    The purpose of this case study was to determine if learning occurred within a 3D virtual learning environment by determining if elements of collaboration and Nonaka and Takeuchi's (1995) knowledge spiral were present. A key portion of this research was the creation of a Virtual Learning Environment. This 3D VLE utilized the Torque Game Engine…

  6. Evolution of Gas Across Spiral Arms in the Whirlpool Galaxy

    NASA Astrophysics Data System (ADS)

    Louie, Melissa Nicole

    To investigate the dynamic evolution of gas across spiral arms, we conducted a detailed study of the gas and star formation along the spiral arms in the Whirlpool Galaxy, M51. This nearby, face-on spiral galaxy provides a unique laboratory to study the relationship between gas dynamics and star formation. The textbook picture of interstellar medium (ISM) evolution is rapidly changing. Molecular gas was once believed to form along spiral arms from the diffuse atomic gas in the inter-arm regions. Star formation occurs within giant molecular clouds during spiral arm passage. Lastly, the molecular gas is photo-dissociated back into atomic gas by massive stars on the downstream side of the spiral arm. Recent evidence, however, is revealing a new picture of the interstellar medium and the process of star formation. We seek development of a new picture by studying the development and evolution of molecular gas and the role of large scale galactic dynamics in organizing the interstellar medium. This thesis begins by presenting work measuring the geometrical offsets between interstellar gas and recent star formation. Interstellar gas is traced by atomic hydrogen and carbon monoxide (CO). Star formation is traced by ionized hydrogen recombination lines and infrared emission from dust warmed by young bright stars. Measuring these offsets can help determine the underlying large scale galactic dynamics. Along the spiral arms in M51, offsets between CO and the star formation tracers suggest that gas is flowing through the spiral arms, but the offsets do not show the expected signature of a single pattern speed and imply a more complicated pattern. This thesis also examines the intermediate stages of gas evolution, by studying a denser component of the ISM closer to which stars will form. Only a small percent of the bulk molecular gas will become dense enough to form stars. HCN and HCO+ probe densities ˜104 cm-3, where as the bulk gas is 500 cm-3. This thesis looks at HCN and

  7. Model for Simulating a Spiral Software-Development Process

    NASA Technical Reports Server (NTRS)

    Mizell, Carolyn; Curley, Charles; Nayak, Umanath

    2010-01-01

    A discrete-event simulation model, and a computer program that implements the model, have been developed as means of analyzing a spiral software-development process. This model can be tailored to specific development environments for use by software project managers in making quantitative cases for deciding among different software-development processes, courses of action, and cost estimates. A spiral process can be contrasted with a waterfall process, which is a traditional process that consists of a sequence of activities that include analysis of requirements, design, coding, testing, and support. A spiral process is an iterative process that can be regarded as a repeating modified waterfall process. Each iteration includes assessment of risk, analysis of requirements, design, coding, testing, delivery, and evaluation. A key difference between a spiral and a waterfall process is that a spiral process can accommodate changes in requirements at each iteration, whereas in a waterfall process, requirements are considered to be fixed from the beginning and, therefore, a waterfall process is not flexible enough for some projects, especially those in which requirements are not known at the beginning or may change during development. For a given project, a spiral process may cost more and take more time than does a waterfall process, but may better satisfy a customer's expectations and needs. Models for simulating various waterfall processes have been developed previously, but until now, there have been no models for simulating spiral processes. The present spiral-process-simulating model and the software that implements it were developed by extending a discrete-event simulation process model of the IEEE 12207 Software Development Process, which was built using commercially available software known as the Process Analysis Tradeoff Tool (PATT). Typical inputs to PATT models include industry-average values of product size (expressed as number of lines of code

  8. Metastudy of the Spiral Structure of Our Home Galaxy

    NASA Astrophysics Data System (ADS)

    Vallée, Jacques P.

    2002-02-01

    The current maps of the Milky Way disk still have large differences, much like early maps of the Earth's continents made in the 16th century had sizeable differences in the locations of continents and many areas labeled ``terra incognita.'' Exactly where are the spiral arms in our home Galaxy (in radius and longitude)? Here a meta-analysis is made of the recent (1995-2001) observational data on the pitch angle (p) and the number (m) of spiral arms in our home Galaxy. In order to clarify our image of the structure of the Milky Way, logarithmic model arms of the form ln(r/r0)=k(θ-θ0) are fitted to the observed tangents to the spiral arms and to the observed position angle (P.A.) of the Galaxy's central bar. The main results are that p=12deg inward and m=4, with logarithmic spiral arm parameters r0=2.3 kpc and θ0=0deg for the Norma arm. The value of θ0 for the other three arms is modeled by rotating the Norma arm in steps of 90°. These values are similar to those found by Ortiz & Lépine using earlier observational data, with some differences. The best model predicts an interarm distance near the Sun of S=2.5 kpc (from the Sagittarius to the Perseus arm) and a distance from the Sun to the Sagittarius arm of 0.9 kpc. These values are compared to our limited and uncertain data from the observed nearby spiral arms. These predicted values near the Sun differ substantially from the predictions of Ortiz & Lépine, as discussed in the text.

  9. Algorithm for hyperfast cone-beam spiral backprojection.

    PubMed

    Steckmann, Sven; Knaup, Michael; Kachelriess, Marc

    2010-06-01

    Cone-beam spiral backprojection is computationally highly demanding. At first sight, the backprojection requirements are similar to those of cone-beam backprojection from circular scans such as it is performed in the widely used Feldkamp algorithm. However, there is an additional complication: the illumination of each voxel, i.e. the range of angles the voxel is seen by the X-ray cone is a complex function of the voxel position. The weight function has no analytically closed form and must be numerically determined. Storage of the weights is prohibitive since the amount of memory required equals the number of voxels per spiral rotation times the number of projections a voxel receives contributions and therefore is in the order of 10(9) to 10(11) floating point values for typical spiral scans. We propose a new algorithm that combines the spiral symmetry with the ability of today's 64 bit CPUs to store large amounts of precomputed weights. Using the spiral symmetry in this way allows to exploit data-level parallelism and thereby to achieve a very high level of vectorization. An additional postprocessing step rotates these slices back to normal images. Our new backprojection algorithm achieves up to 24.6 Giga voxel updates per second (GUPS) on our systems that are equipped with two standard Intel X5570 quad core CPUs (Intel Xeon 5500 platform, 2.93 GHz, Intel Corporation). This equals the reconstruction of 410 images per second assuming each slice consists of 512 x 512 pixels, receiving contributions from 512 projections. PMID:19765852

  10. Slowly breaking waves: the longevity of tidally induced spiral structure

    NASA Astrophysics Data System (ADS)

    Struck, Curtis; Dobbs, Clare L.; Hwang, Jeong-Sun

    2011-07-01

    We have discovered long-lived waves in two sets of numerical models of fast (marginally bound or unbound) flyby galaxy collisions, carried out independently with two different codes. In neither simulation set are the spirals the result of a collision-induced bar formation. Although there is variation in the appearance of the waves with time, they do not disappear and reform recurrently, as seen in other cases described in the literature. We also present an analytic theory that can account for the wave structure, not as propagating transients, nor as a fixed pattern propagating through the disc. While these waves propagate through the disc, they are mantained by the coherent oscillations initiated by the impulsive disturbance. Specifically, the analytic theory suggests that they are caustic waves in ensembles of stars pursuing correlated epicyclic orbits after the disturbance. This theory is an extension of that developed by Struck and collaborators for colliding ring galaxies. The models suggest that this type of wave may persist for a couple of Gyr, and galaxy interactions occur on comparable time-scales, so waves produced by the mechanism may be well represented in observed spirals. In particular, this mechanism can account for the tightly wound, and presumably long-lived, spirals seen in some nearby early-type galaxies. These spirals are also likely to be common in groups and clusters, where fast encounters between galaxies occur relatively frequently. However, as the spirals become tightly wound, and evolve to modest amplitudes, they may be difficult to resolve unless they are nearby. None the less, the effect may be one of several processes that result from galaxy harassment, and via wave-enhanced star formation, contributes to the Butcher-Oemler effect.

  11. SU-E-I-98: Dose Comparison for Pulmonary Embolism CT Studies: Single Energy Vs. Dual Energy

    SciTech Connect

    Mahmood, U; Erdi, Y

    2014-06-01

    Purpose: The purpose of this study was to assess and compare the size specific dose estimate (SSDE), dose length product (DLP) and noise relationship for pulmonary embolism studies evaluated by single source dual energy computed tomography (DECT) against conventional CT (CCT) studies in a busy cancer center and to determine the dose savings provided by DECT. Methods: An IRB-approved retrospective study was performed to determine the CTDIvol and DLP from a subset of patients scanned with both DECT and CCT over the past five years. We were able to identify 30 breast cancer patients (6 male, 24 female, age range 24 to 81) who had both DECT and CCT studies performed. DECT scans were performed with a GE HD 750 scanner (140/80 kVp, 480 mAs and 40 mm) and CCT scans were performed with a GE Lightspeed 16 slice scanner (120 kVp, 352 mAs, 20 mm). Image noise was measured by placing an ROI and recording the standard deviation of the mean HU along the descending aorta. Results: The average DECT patient size specific dose estimate was to be 14.2 ± 1.7 mGy as compared to 22.4 ± 2.7 mGy from CCT PE studies, which is a 37% reduction in the SSDE. The average DECT DLP was 721.8 ± 84.6 mGy-cm as compared to 981.8 ± 106.1 mGy-cm for CCT, which is a 26% decrease. Compared to CCT the image noise was found to decrease by 19% when using DECT for PE studies. Conclusion: DECT SSDE and DLP measurements indicate dose savings and image noise reduction when compared to CCT. In an environment that heavily debates CT patient doses, this study confirms the effectiveness of DECT in PE imaging.

  12. Pediatric CT Scans

    Cancer.gov

    The Radiation Epidemiology Branch and collaborators have initiated a retrospective cohort study to evaluate the relationship between radiation exposure from CT scans conducted during childhood and adolescence and the subsequent development of cancer.

  13. Head CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. While inside the scanner, the machine's x-ray beam rotates around you. ... breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and ...

  14. Arm CT scan

    MedlinePlus

    CAT scan - arm; Computed axial tomography scan - arm; Computed tomography scan - arm; CT scan - arm ... Mosby; 2013:chap 57. Shaw AS, Prokop M. Computed tomography. In: Adam A, Dixon AK, Gillard JH, Schaefer- ...

  15. Heart CT scan

    MedlinePlus

    CAT scan - heart; Computed axial tomography scan - heart; Computed tomography scan - heart; Calcium scoring; Multi-detector CT scan - heart; Electron beam computed tomography - heart; Agaston score; Coronary calcium scan

  16. Sinus CT scan

    MedlinePlus

    CAT scan - sinus; Computed axial tomography scan - sinus; Computed tomography scan - sinus; CT scan - sinus ... 2014:chap 67. Shaw AS, Dixon AK. Multidetector computed tomography. In: Adam A, Dixon AK, eds. Grainger & Allison's ...

  17. Leg CT scan

    MedlinePlus

    CAT scan - leg; Computed axial tomography scan - leg; Computed tomography scan - leg; CT scan - leg ... Saunders; 2012:chap 11. Shaw AS, Prokop M. Computed tomography. In: Adam A, Dixon AK, Gillard JH, Schaefer- ...

  18. Pelvic CT scan

    MedlinePlus

    CAT scan - pelvis; Computed axial tomography scan - pelvis; Computed tomography scan - pelvis; CT scan - pelvis ... gov/pubmed/18381118 . Shaw AS, Dixon AK. Multidetector computed tomography. In: Grainger RC, Allison D, Adam, Dixon AK, ...

  19. Shoulder CT scan

    MedlinePlus

    CAT scan - shoulder; Computed axial tomography scan - shoulder; Computed tomography scan - shoulder; CT scan - shoulder ... Mosby; 2012:chap 57. Shaw AS, Prokop M. Computed tomography. In: Adam A, Dixon AK, Gillard JH, Schaefer- ...

  20. Lumbar spine CT scan

    MedlinePlus

    CAT scan - lumbar spine; Computed axial tomography scan - lumbar spine; Computed tomography scan - lumbar spine; CT - lower back ... stopping.) A computer creates separate images of the spine area, called slices. These images can be stored, ...

  1. Chest CT Scan

    MedlinePlus

    ... pictures to create a very detailed, three-dimensional (3D) model of organs. Sometimes, a substance called contrast dye is injected into a vein in your arm for the CT scan. This substance highlights areas in your chest, which ...

  2. CT Colonography (Virtual Colonoscopy)

    MedlinePlus

    ... into the colon using a hand-held squeeze bulb. Sometimes an electronic pump is used to deliver ... When you enter the CT scanner room, special light lines may be seen projected onto your body, ...

  3. CT Angiography (CTA)

    MedlinePlus

    ... CT Angiography? Angiography is a minimally invasive medical test that helps physicians diagnose and treat medical conditions. Angiography uses one of three imaging technologies and, in most cases, a contrast material injection ...

  4. Of circles and spirals: bridging the gap between the leading circle and spiral wave concepts of cardiac reentry.

    PubMed

    Comtois, P; Kneller, J; Nattel, S

    2005-09-01

    The "leading circle model" was the first detailed attempt at understanding the mechanisms of functional reentry, and remains a widely-used notion in cardiac electrophysiology. The "spiral wave" concept was developed more recently as a result of modern theoretical analysis and is the basis for consideration of reentry mechanisms in present biophysical theory. The goal of this paper is to present these models in a way that is comprehensible to both the biophysical and electrophysiology communities, with the idea of helping clinical and experimental electrophysiologists to understand better the spiral wave concept and of helping biophysicists to understand why the leading circle concept is so attractive and widely used by electrophysiologists. To this end, the main properties of the leading circle and spiral wave models of reentry are presented. Their basic assumptions and determinants are discussed and the predictions of the two concepts with respect to pharmacological responses of arrhythmias are reviewed. A major difference between them lies in the predicted responses to Na(+)-channel blockade, for which the spiral wave paradigm appears more closely to correspond to the results of clinical and experimental observations. The basis of this difference is explored in the context of the fundamental properties of the models. PMID:16102499

  5. CT angiography after 20 years: a transformation in cardiovascular disease characterization continues to advance.

    PubMed

    Rubin, Geoffrey D; Leipsic, Jonathon; Joseph Schoepf, U; Fleischmann, Dominik; Napel, Sandy

    2014-06-01

    Through a marriage of spiral computed tomography (CT) and graphical volumetric image processing, CT angiography was born 20 years ago. Fueled by a series of technical innovations in CT and image processing, over the next 5-15 years, CT angiography toppled conventional angiography, the undisputed diagnostic reference standard for vascular disease for the prior 70 years, as the preferred modality for the diagnosis and characterization of most cardiovascular abnormalities. This review recounts the evolution of CT angiography from its development and early challenges to a maturing modality that has provided unique insights into cardiovascular disease characterization and management. Selected clinical challenges, which include acute aortic syndromes, peripheral vascular disease, aortic stent-graft and transcatheter aortic valve assessment, and coronary artery disease, are presented as contrasting examples of how CT angiography is changing our approach to cardiovascular disease diagnosis and management. Finally, the recently introduced capabilities for multispectral imaging, tissue perfusion imaging, and radiation dose reduction through iterative reconstruction are explored with consideration toward the continued refinement and advancement of CT angiography. PMID:24848958

  6. Improving electricity production in tubular microbial fuel cells through optimizing the anolyte flow with spiral spacers.

    PubMed

    Zhang, Fei; Ge, Zheng; Grimaud, Julien; Hurst, Jim; He, Zhen

    2013-04-01

    The use of spiral spacers to create a helical flow for improving electricity generation in microbial fuel cells (MFCs) was investigated in both laboratory and on-site tests. The lab tests found that the MFC with the spiral spacers produced more electricity than the one without the spiral spacers at different recirculation rates or organic loading rates, likely due to the improved transport/distribution of ions and electron mediators instead of the substrates because the organic removal efficiency was not obviously affected by the presence of the spiral spacers. The energy production in the MFC with the spiral spacers reached 0.071 or 0.073 kWh/kg COD in either vertical or horizontal installment. The examination of the MFCs installed in an aeration tank of a municipal wastewater treatment plant confirmed the advantage of using the spiral spacers. Those results demonstrate that spiral spacers could be an effective approach to improve energy production in MFCs. PMID:23500582

  7. Spiral-in/out BOLD fMRI for increased SNR and reduced susceptibility artifacts.

    PubMed

    Glover, G H; Law, C S

    2001-09-01

    BOLD fMRI is hampered by dropout of signal in the orbitofrontal and parietal brain regions due to magnetic field gradients near air-tissue interfaces. This work reports the use of spiral-in trajectories that begin at the edge of k-space and end at the origin, and spiral in/out trajectories in which a spiral-in readout is followed by a conventional spiral-out trajectory. The spiral-in trajectory reduces the dropout and increases the BOLD contrast. The spiral-in and spiral-out images can be combined in several ways to simultaneously achieve increased signal-to-noise ratio (SNR) and reduced dropout artifacts. Activation experiments employing an olfaction task demonstrate significantly increased activation volumes due to reduced dropout, and overall increased SNR in all regions. PMID:11550244

  8. Magnetic and gaseous spiral arms in M83

    NASA Astrophysics Data System (ADS)

    Frick, P.; Stepanov, R.; Beck, R.; Sokoloff, D.; Shukurov, A.; Ehle, M.; Lundgren, A.

    2016-01-01

    Context. The magnetic field configurations in several nearby spiral galaxies contain magnetic arms that are sometimes located between the material arms. The nearby barred galaxy M83 provides an outstanding example of a spiral pattern seen in tracers of gas and magnetic field. Aims: We analyse the spatial distribution of magnetic fields in M83 and their relation to the material spiral arms. Methods: Isotropic and anisotropic wavelet transforms are used to decompose the images of M83 in various tracers to quantify structures in a range of scales from 0.2 to 10 kpc. We used radio polarization observations at λ6.2 cm and λ13 cm obtained with the VLA, Effelsberg and ATCA telescopes and APEX sub-mm observations at 870 μm, which are first published here, together with maps of the emission of warm dust, ionized gas, molecular gas, and atomic gas. Results: The spatial power spectra are similar for the tracers of dust, gas, and total magnetic field, while the spectra of the ordered magnetic field are significantly different. As a consequence, the wavelet cross-correlation between all material tracers and total magnetic field is high, while the structures of the ordered magnetic field are poorly correlated with those of other tracers. The magnetic field configuration in M83 contains pronounced magnetic arms. Some of them are displaced from the corresponding material arms, while others overlap with the material arms. The pitch angles of the magnetic and material spiral structures are generally similar. The magnetic field vectors at λ6.2 cm are aligned with the outer material arms, while significant deviations occur in the inner arms and, in particular, in the bar region, possibly due to non-axisymmetric gas flows. Outside the bar region, the typical pitch angles of the material and magnetic spiral arms are very close to each other at about 10°. The typical pitch angle of the magnetic field vectors is about 20° larger than that of the material spiral arms. Conclusions

  9. Star Formation in Partially Gas-Depleted Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Rose, James A.; Robertson, Paul; Miner, Jesse; Levy, Lorenza

    2010-02-01

    Broadband B and R and Hα images have been obtained with the 4.1 m SOAR telescope atop Cerro Pachon, Chile, for 29 spiral galaxies in the Pegasus I galaxy cluster and for 18 spirals in non-cluster environments. Pegasus I is a spiral-rich cluster with a low-density intracluster medium and a low galaxy velocity dispersion. When combined with neutral hydrogen (H I) data obtained with the Arecibo 305 m radio telescope, acquired by Levy et al. (2007) and by Springob et al. (2005b), we study the star formation rates in disk galaxies as a function of their H I deficiency. To quantify H I deficiency, we use the usual logarithmic deficiency parameter, DEF. The specific star formation rate (SSFR) is quantified by the logarithmic flux ratio of Hα flux to R-band flux, and thus roughly characterizes the logarithmic SFR per unit stellar mass. We find a clear correlation between the global SFR per unit stellar mass and DEF, such that the SFR is lower in more H I-deficient galaxies. This correlation appears to extend from the most gas-rich to the most gas-poor galaxies. We also find a correlation between the central SFR per unit mass relative to the global values, in the sense that the more H I-deficient galaxies have a higher central SFR per unit mass relative to their global SFR values than do gas-rich galaxies. In fact, approximately half of the H I-depleted galaxies have highly elevated SSFRs in their central regions, indicative of a transient evolutionary state. In addition, we find a correlation between gas depletion and the size of the Hα disk (relative to the R-band disk); H I-poor galaxies have truncated disks. Moreover, aside from the elevated central SSFR in many gas-poor spirals, the SSFR is otherwise lower in the Hα disks of gas-poor galaxies than in gas-rich spirals. Thus, both disk truncation and lowered SSFR levels within the star-forming part of the disks (aside from the enhanced nuclear SSFR) correlate with H I deficiency, and both phenomena are found to

  10. Diffuse X-Ray Emission in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Tyler, Krystal; Quillen, A. C.; LaPage, Amanda; Rieke, George H.

    2004-07-01

    We compare the soft diffuse X-ray emission from Chandra images of 12 nearby intermediate-inclination spiral galaxies to the morphology seen in Hα, molecular gas, and mid-infrared emission. We find that diffuse X-ray emission is often located along spiral arms in the outer parts of spiral galaxies but tends to be distributed in a more nearly radially symmetric morphology in the center. The X-ray morphology in the spiral arms matches that seen in the mid-infrared or Hα and thus implies that the X-ray emission is associated with recent active star formation. In the spiral arms there is a good correlation between the level of diffuse X-ray emission and that in the mid-infrared in different regions. The correlation between X-ray and mid-IR flux in the galaxy centers is less strong. We also find that the central X-ray emission tends to be more luminous in galaxies with brighter bulges, suggesting that more than one process is contributing to the level of central diffuse X-ray emission. We see no strong evidence for X-ray emission trailing the location of high-mass star formation in spiral arms. However, population synthesis models predict a high mechanical energy output rate from supernovae for a time period that is about 10 times longer than the lifetime of massive ionizing stars, conflicting with the narrow appearance of the arms in X-rays. The fraction of supernova energy that goes into heating the interstellar medium must depend on environment and is probably higher near sites of active star formation. The X-ray estimated emission measures suggest that the volume filling factors and scale heights are low in the outer parts of these galaxies but higher in the galaxy centers. The differences between the X-ray properties and morphology in the centers and outer parts of these galaxies suggest that galactic fountains operate in outer galaxy disks but that winds are primarily driven from galaxy centers.

  11. STAR FORMATION IN PARTIALLY GAS-DEPLETED SPIRAL GALAXIES

    SciTech Connect

    Rose, James A.; Miner, Jesse; Levy, Lorenza; Robertson, Paul E-mail: paul@astr.as.utexas.edu E-mail: lorenza.levy@yahoo.com

    2010-02-15

    Broadband B and R and H{alpha} images have been obtained with the 4.1 m SOAR telescope atop Cerro Pachon, Chile, for 29 spiral galaxies in the Pegasus I galaxy cluster and for 18 spirals in non-cluster environments. Pegasus I is a spiral-rich cluster with a low-density intracluster medium and a low galaxy velocity dispersion. When combined with neutral hydrogen (H I) data obtained with the Arecibo 305 m radio telescope, acquired by Levy et al. (2007) and by Springob et al. (2005b), we study the star formation rates in disk galaxies as a function of their H I deficiency. To quantify H I deficiency, we use the usual logarithmic deficiency parameter, DEF. The specific star formation rate (SSFR) is quantified by the logarithmic flux ratio of H{alpha} flux to R-band flux, and thus roughly characterizes the logarithmic SFR per unit stellar mass. We find a clear correlation between the global SFR per unit stellar mass and DEF, such that the SFR is lower in more H I-deficient galaxies. This correlation appears to extend from the most gas-rich to the most gas-poor galaxies. We also find a correlation between the central SFR per unit mass relative to the global values, in the sense that the more H I-deficient galaxies have a higher central SFR per unit mass relative to their global SFR values than do gas-rich galaxies. In fact, approximately half of the H I-depleted galaxies have highly elevated SSFRs in their central regions, indicative of a transient evolutionary state. In addition, we find a correlation between gas depletion and the size of the H{alpha} disk (relative to the R-band disk); H I-poor galaxies have truncated disks. Moreover, aside from the elevated central SSFR in many gas-poor spirals, the SSFR is otherwise lower in the H{alpha} disks of gas-poor galaxies than in gas-rich spirals. Thus, both disk truncation and lowered SSFR levels within the star-forming part of the disks (aside from the enhanced nuclear SSFR) correlate with H I deficiency, and both

  12. Allosaurus, crocodiles, and birds: evolutionary clues from spiral computed tomography of an endocast.

    PubMed

    Rogers, S W

    1999-10-15

    Because the brain does not usually leave direct evidence of its existence in the fossil record, our view of this structure in extinct species has relied upon inferences drawn from comparisons between parts of the skeleton that do fossilize or with modern-day relatives that survived extinction. However, soft-tissue structure preservation may indeed occasionally occur, particularly in the endocranial space. By applying modern imaging and analysis methods to such natural cranial "endocasts," we can now learn more than ever thought possible about the brains of extinct species. I will discuss one such example in which spiral computed tomography (CT) scanning analysis has been successfully applied to reveal preserved internal structures of a naturally occurring endocranial cast of Allosaurus fragilis, the dominant carnivorous dinosaur of the late Jurassic period. The ability to directly examine the neuroanatomy of an extinct dinosaur, whose modern-day relatives are birds and crocodiles, has exciting implications about Allosaurus' behavior, its adaptive responses to its environment, and its eventual extinction. PMID:10597341

  13. Experimental measurement on movement of spiral-type capsule endoscope

    PubMed Central

    Yang, Wanan; Dai, Houde; He, Yong; Qin, Fengqing

    2016-01-01

    Wireless capsule endoscope achieved great success, however, the maneuvering of wireless capsule endoscope is challenging at present. A magnetic driving instrument, including two bar magnets, a stepper motor, a motor driver, a motor controller, and a power supplier, was developed to generate rotational magnetic fields. Permanent magnet ring, magnetized as S and N poles radially and mounted spiral structure on the surface, acted as a capsule. The maximum torque passing to the capsule, rotational synchronization of capsule and motor, and the translational speed of capsule, were measured in ex vivo porcine large intestine. The experimental results illustrate that the rotational movement of the spiral-type capsule in the intestine is feasible and the cost of the magnetic driving equipment is low. As a result, the solution is promising in the future controllability. PMID:26848279

  14. Local interstellar gasdynamical stability in spiral arm flow

    NASA Technical Reports Server (NTRS)

    Balbus, S. A.

    1986-01-01

    The stability of two-dimensional interstellar gas flow passing through a spiral potential has been investigated. The background flow is assumed to move in a tightly wound potential, which may be regarded as external or self-generated. The unperturbed flow, which may be time dependent, is self-gravitating and satisfies the Roberts equations of motion. A polytropic, single-fluid assumption has been used. Magnetic effects are not considered. The motivation behind this work is to try to understand how much of the diversity of spiral arm morphology can be understood by large scale gas dynamical processes alone. To this end, it is suggested that spurring and feathering, and forming molecular cloud complexes may be closely related in the sense of having dynamically similar origins.

  15. Experimental measurement on movement of spiral-type capsule endoscope.

    PubMed

    Yang, Wanan; Dai, Houde; He, Yong; Qin, Fengqing

    2016-01-01

    Wireless capsule endoscope achieved great success, however, the maneuvering of wireless capsule endoscope is challenging at present. A magnetic driving instrument, including two bar magnets, a stepper motor, a motor driver, a motor controller, and a power supplier, was developed to generate rotational magnetic fields. Permanent magnet ring, magnetized as S and N poles radially and mounted spiral structure on the surface, acted as a capsule. The maximum torque passing to the capsule, rotational synchronization of capsule and motor, and the translational speed of capsule, were measured in ex vivo porcine large intestine. The experimental results illustrate that the rotational movement of the spiral-type capsule in the intestine is feasible and the cost of the magnetic driving equipment is low. As a result, the solution is promising in the future controllability. PMID:26848279

  16. The black hole mass function derived from local spiral galaxies

    SciTech Connect

    Davis, Benjamin L.; Berrier, Joel C.; Shields, Douglas W.; Kennefick, Daniel; Kennefick, Julia; Seigar, Marc S.; Lacy, Claud H. S.; Hartley, Matthew T.

    2014-07-10

    We present our determination of the nuclear supermassive black hole (SMBH) mass function for spiral galaxies in the local universe, established from a volume-limited sample consisting of a statistically complete collection of the brightest spiral galaxies in the southern (δ < 0°) hemisphere. Our SMBH mass function agrees well at the high-mass end with previous values given in the literature. At the low-mass end, inconsistencies exist in previous works that still need to be resolved, but our work is more in line with expectations based on modeling of black hole evolution. This low-mass end of the spectrum is critical to our understanding of the mass function and evolution of black holes since the epoch of maximum quasar activity. The sample is defined by a limiting luminosity (redshift-independent) distance, D{sub L} = 25.4 Mpc (z = 0.00572) and a limiting absolute B-band magnitude, M{sub B}=−19.12. These limits define a sample of 140 spiral galaxies, with 128 measurable pitch angles to establish the pitch angle distribution for this sample. This pitch-angle distribution function may be useful in the study of the morphology of late-type galaxies. We then use an established relationship between the logarithmic spiral arm pitch angle and the mass of the central SMBH in a host galaxy in order to estimate the mass of the 128 respective SMBHs in this volume-limited sample. This result effectively gives us the distribution of mass for SMBHs residing in spiral galaxies over a lookback time, t{sub L} ≤ 82.1 h{sub 67.77}{sup −1} Myr and contained within a comoving volume, V{sub C} = 3.37 × 10{sup 4} h{sub 67.77}{sup −3} Mpc{sup 3}. We estimate that the density of SMBHs residing in spiral galaxies in the local universe is ρ=5.54{sub −2.73}{sup +6.55} × 10{sup 4} h{sub 67.77}{sup 3} M{sub ☉} Mpc{sup –3}. Thus, our derived cosmological SMBH mass density for spiral galaxies is Ω{sub BH}=4.35{sub −2.15}{sup +5.14} × 10{sup –7} h{sub 67.77}. Assuming that

  17. Spiral actin-polymerization waves can generate amoeboidal cell crawling

    NASA Astrophysics Data System (ADS)

    Dreher, A.; Aranson, I. S.; Kruse, K.

    2014-05-01

    Amoeboidal cell crawling on solid substrates is characterized by protrusions that seemingly appear randomly along the cell periphery and drive the cell forward. For many cell types, it is known that the protrusions result from polymerization of the actin cytoskeleton. However, little is known about how the formation of protrusions is triggered and whether the appearance of subsequent protrusions is coordinated. Recently, the spontaneous formation of actin-polymerization waves was observed. These waves have been proposed to orchestrate the cytoskeletal dynamics during cell crawling. Here, we study the impact of cytoskeletal polymerization waves on cell migration using a phase-field approach. In addition to directionally moving cells, we find states reminiscent of amoeboidal cell crawling. In this framework, new protrusions are seen to emerge from a nucleation process, generating spiral actin waves in the cell interior. Nucleation of new spirals does not require noise, but occurs in a state that is apparently displaying spatio-temporal chaos.

  18. Far-infrared emission and star formation in spiral galaxies

    NASA Technical Reports Server (NTRS)

    Trinchieri, G.; Fabbiano, G.; Bandiera, R.

    1989-01-01

    The correlations between the emission in the far-IR, H-alpha, and blue in a sample of normal spiral galaxies are investigated. It is found that the luminosities in these three bands are all tightly correlated, although both the strength of the correlations and their functional dependencies are a function of the galaxies' morphological types. The best-fit power laws to these correlations are different for the comparison of different quantities and deviate significantly from linearity in some cases, implying the presence of additional emission mechanisms not related to the general increase of luminosity with galactic mass. Clear evidence is found of two independent effects in the incidence of warm far-IR emission in late-type spirals. One is a luminosity effect shown by the presence of excess far-IR relative to H-alpha or optical emission in the more luminous galaxies. The other is a dependence on widespread star-formation activity.

  19. Spiral defect chaos in an advection-reaction-diffusion system

    NASA Astrophysics Data System (ADS)

    Affan, H.; Friedrich, R.

    2014-06-01

    This paper comprises numerical and theoretical studies of spatiotemporal patterns in advection-reaction-diffusion systems in which the chemical species interact with the hydrodynamic fluid. Due to the interplay between the two, we obtained the spiral defect chaos in the activator-inhibitor-type model. We formulated the generalized Swift-Hohenberg-type model for this system. Then the evolution of fractal boundaries due to the effect of the strong nonlinearity at the interface of the two chemical species is studied numerically. The purpose of the present paper is to point out that spiral defect chaos, observed in model equations of the extended Swift-Hohenberg equation for low Prandtl number convection, may actually be obtained also in certain advection-reaction-diffusion systems.

  20. 2 Degree-of-Freedom Spiral Micromirror Manipulator

    NASA Astrophysics Data System (ADS)

    Sadat, Seid Hossein; Kamiya, Daiki; Bagheri, Saeed; Horie, Mikio

    We present a process for the fabrication and assembly of a novel spiral-shaped micromirror manipulator for free space optical switching. The manipulator is comprised of two different parts, which are fabricated using conventional surface micromachining processes. The footprint of the assembled device is about 600μm and the height of the micro pyramid is 200μm. In spite of conventional approaches to microsystem design, which prefer devices with monolithic and self-assembling properties, the two parts are fabricated on two different chips. They are then assembled using a spatial mechanical approach. A number of separate spiral and pyramid parts are fabricated and the first assembling test on a single actuator is performed. In this paper, the Surface micromachining processes used for fabrication of the parts are presented and their sensitivity and issues are discussed. Spatial mechanical assembly results are presented and process issues are addressed.

  1. Heating hydrocarbon containing formations in a spiral startup staged sequence

    SciTech Connect

    Vinegar, Harold J.; Miller, David Scott

    2009-12-15

    Methods for treating a hydrocarbon containing formation are described herein. Methods may include treating a first zone of the formation. Treatment of a plurality of zones of the formation may be begun at selected times after the treatment of the first zone begins. The treatment of at least two successively treated zones may begin at a selected time after treatment of the previous zone begins. At least two of the successively treated zones may be adjacent to the zone treated previously. The successive treatment of the zones proceeds in an outward, substantially spiral sequence from the first zone so that the treatment of the zones may move substantially spirally outwards towards a boundary of the treatment area.

  2. Spiral and never-settling patterns in active systems

    NASA Astrophysics Data System (ADS)

    Yang, X.; Marenduzzo, D.; Marchetti, M. C.

    2014-01-01

    We present a combined numerical and analytical study of pattern formation in an active system where particles align, possess a density-dependent motility, and are subject to a logistic reaction. The model can describe suspensions of reproducing bacteria, as well as polymerizing actomyosin gels in vitro or in vivo. In the disordered phase, we find that motility suppression and growth compete to yield stable or blinking patterns, which, when dense enough, acquire internal orientational ordering to give asters or spirals. We predict these may be observed within chemotactic aggregates in bacterial fluids. In the ordered phase, the reaction term leads to previously unobserved never-settling patterns which can provide a simple framework to understand the formation of motile and spiral patterns in intracellular actin systems.

  3. Spiral and never-settling patterns in active systems.

    PubMed

    Yang, X; Marenduzzo, D; Marchetti, M C

    2014-01-01

    We present a combined numerical and analytical study of pattern formation in an active system where particles align, possess a density-dependent motility, and are subject to a logistic reaction. The model can describe suspensions of reproducing bacteria, as well as polymerizing actomyosin gels in vitro or in vivo. In the disordered phase, we find that motility suppression and growth compete to yield stable or blinking patterns, which, when dense enough, acquire internal orientational ordering to give asters or spirals. We predict these may be observed within chemotactic aggregates in bacterial fluids. In the ordered phase, the reaction term leads to previously unobserved never-settling patterns which can provide a simple framework to understand the formation of motile and spiral patterns in intracellular actin systems. PMID:24580261

  4. Charge breeder for the SPIRAL1 upgrade: Preliminary results

    NASA Astrophysics Data System (ADS)

    Maunoury, L.; Delahaye, P.; Dubois, M.; Angot, J.; Sole, P.; Bajeat, O.; Barton, C.; Frigot, R.; Jeanne, A.; Jardin, P.; Kamalou, O.; Lecomte, P.; Osmond, B.; Peschard, G.; Lamy, T.; Savalle, A.

    2016-02-01

    In the framework of the SPIRAL1 upgrade under progress at the GANIL lab, the charge breeder based on a LPSC Phoenix ECRIS, first tested at ISOLDE has been modified to benefit of the last enhancements of this device from the 1+/n+ community. The modifications mainly concern the 1 + optics, vacuum techniques, and the RF—buffer gas injection into the charge breeder. Prior to its installation in the midst of the low energy beam line of the SPIRAL1 facility, it has been decided to qualify its performances and several operation modes at the test bench of LPSC lab. This contribution shall present preliminary results of experiments conducted at LPSC concerning the 1 + to n+ conversion efficiencies for noble gases as well as for alkali elements and the corresponding transformation times.

  5. Spiral-Bevel-Gear Damage Detected Using Decision Fusion Analysis

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Handschuh, Robert F.

    2003-01-01

    Helicopter transmission integrity is critical to helicopter safety because helicopters depend on the power train for propulsion, lift, and flight maneuvering. To detect impending transmission failures, the ideal diagnostic tools used in the health-monitoring system would provide real-time health monitoring of the transmission, demonstrate a high level of reliable detection to minimize false alarms, and provide end users with clear information on the health of the system without requiring them to interpret large amounts of sensor data. A diagnostic tool for detecting damage to spiral bevel gears was developed. (Spiral bevel gears are used in helicopter transmissions to transfer power between nonparallel intersecting shafts.) Data fusion was used to integrate two different monitoring technologies, oil debris analysis and vibration, into a health-monitoring system for detecting surface fatigue pitting damage on the gears.

  6. Millimeter-wave generation with spiraling electron beams

    NASA Technical Reports Server (NTRS)

    Kulke, B.

    1971-01-01

    The feasibility of using the interaction between a thin, solid, spiraling electron beam of 10 to 20 kV energy and a microwave cavity to generate watts of CW millimeter-wave power was investigated. Experimental results are given for several prototype devices operating at 9.4 GHz and at 94 GHz. Power outputs of 5 W, and electronic efficiencies near 3%, were obtained at X band, and moderate gain was obtained at 94 GHz. The small-signal theory gives a good fit to the X-band data, and the device behavior at 94 GHz is as expected from the given beam characteristics. The performance is limited chiefly by the velocity spread in the spiraling electron beam, and once this can be brought under control, high-power generation of millimeter waves appears quite feasible with this type of device.

  7. Spitzer Observations of Extraplanar PAH Emission from Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Lehner, N.; Howk, J.

    We present Spitzer/IRAC observations of polycylic aromatic hydrocarbon (PAH) emission from interstellar material in the thick disks of normal spiral galaxies. These data show PAHs to be a common constituent of extraplanar material in spirals. The processes that displace this material from the interstellar disks of these systems do not destroy these very small grains. The dust emission features are present far above the galactic planes, extended up to about 2-4 kpc above the midplanes of the galaxies presented in this work. The total extent for which dust can be traced is about half the extent of the DIG. If it is not a sensitivity effect, this suggests that PAHs may be associated with a cold neutral medium that can not be supported at high z.

  8. Cosmic ray acceleration by spiral shocks in the galactic wind

    NASA Astrophysics Data System (ADS)

    Völk, H. J.; Zirakashvili, V. N.

    2004-04-01

    Cosmic ray acceleration by shocks related with Slipping Interaction Regions (SIRs) in the Galactic Wind is considered. SIRs are similar to Solar Wind Corotating Interaction Regions. The spiral structure of our Galaxy results in a strong nonuniformity of the Galactic Wind flow and in SIR formation at distances of 50 to 100 kpc. SIRs are not corotating with the gas and magnetic field because the angular velocity of the spiral pattern differs from that of the Galactic rotation. It is shown that the collective reacceleration of the cosmic ray particles with charge Ze in the resulting shock ensemble can explain the observable cosmic ray spectrum beyond the ``knee'' up to energies of the order of 1017 Z eV. For the reaccelerated particles the Galactic Wind termination shock acts as a reflecting boundary.

  9. Spiral and croissant crack in drying thin films

    NASA Astrophysics Data System (ADS)

    Marthelot, Joel; Roman, Benoit; Bico, Jose; Barthel, Etienne; Teisseire, Jeremie; Dalmas, Davy; Melo, Francisco

    2012-02-01

    Drying mud or crazing in ceramics glaze leads to familiar hierarchical cracks network where a new crack connects perpendicularly to older ones. We report unusual spirals and croissants crack patterns in methylsiloxane drying thin films moderately adhering on a substrate. Such cracks are also observed in a very different situation when magnetron sputtering multilayers are under external tension. The amplitude and wavelength of the pattern are robusts and are orders of magnitude larger than the thickness of the layer. The propagation of the spiral and croissant cracks occurs in a narrow range of adhesion energy between the film and the substrate and strain in the film. We will show how the propagation is driven by a cooperation between fracture and adhesion.

  10. A Survey of nearby, nearly face-on spiral galaxies

    NASA Astrophysics Data System (ADS)

    Garmire, Gordon

    2014-09-01

    This is a continuation of a survey of nearby, nearly face-on spiral galaxies. The main purpose is to search for evidence of collisions with small galaxies that show up in X-rays by the generation of hot shocked gas from the collision. Secondary objectives include study of the spatial distribution point sources in the galaxy and to detect evidence for a central massive blackhole. These are alternate targets.

  11. A Survey of nearby, nearly face-on spiral galaxies

    NASA Astrophysics Data System (ADS)

    Garmire, Gordon

    2014-09-01

    This is a continuation of a survey of nearby, nearly face-on spiral galaxies. The main purpose is to search for evidence of collisions with small galaxies that show up in X-rays by the generation of hot shocked gas from the collision. Secondary objectives include study of the spatial distribution point sources in the galaxy and to detect evidence for a central massive blackhole.

  12. Spiral and Rotor Patterns Produced by Fairy Ring Fungi

    NASA Astrophysics Data System (ADS)

    Karst, N.; Dralle, D.; Thompson, S. E.

    2015-12-01

    Soil fungi fill many essential ecological and biogeochemical roles, e.g. decomposing litter, redistributing nutrients, and promoting biodiversity. Fairy ring fungi offer a rare glimpse into the otherwise opaque spatiotemporal dynamics of soil fungal growth, because subsurface mycelial patterns can be inferred from observations at the soil's surface. These observations can be made directly when the fungi send up fruiting bodies (e.g., mushrooms and toadstools), or indirectly via the effect the fungi have on neighboring organisms. Grasses in particular often temporarily thrive on the nutrients liberated by the fungus, creating bands of rich, dark green turf at the edge of the fungal mat. To date, only annular (the "ring" in fairy ring) and arc patterns have been described in the literature. We report observations of novel spiral and rotor pattern formation in fairy ring fungi, as seen in publically available high-resolution aerial imagery of 22 sites across the continental United States. To explain these new behaviors, we first demonstrate that a well-known model describing fairy ring formation is equivalent to the Gray-Scott reaction-diffusion model, which is known to support a wide range of dynamical behaviors, including annular traveling waves, rotors, spirals, and stable spatial patterns including spots and stripes. Bifurcation analysis and numerical simulation are then used to define the region of parameter space that supports spiral and rotor formation. We find that this region is adjacent to one within which typical fairy rings develop. Model results suggest simple experimental procedures that could potentially induce traditional ring structures to exhibit rotor or spiral dynamics. Intriguingly, the Gray-Scott model predicts that these same procedures could be used to solicit even richer patterns, including spots and stripes, which have not yet been identified in the field.

  13. Simulating Fatigue Crack Growth in Spiral Bevel Pinion

    NASA Technical Reports Server (NTRS)

    Ural, Ani; Wawrzynek, Paul A.; Ingraffe, Anthony R.

    2003-01-01

    This project investigates computational modeling of fatigue crack growth in spiral bevel gears. Current work is a continuation of the previous efforts made to use the Boundary Element Method (BEM) to simulate tooth-bending fatigue failure in spiral bevel gears. This report summarizes new results predicting crack trajectory and fatigue life for a spiral bevel pinion using the Finite Element Method (FEM). Predicting crack trajectories is important in determining the failure mode of a gear. Cracks propagating through the rim may result in catastrophic failure, whereas the gear may remain intact if one tooth fails and this may allow for early detection of failure. Being able to predict crack trajectories is insightful for the designer. However, predicting growth of three-dimensional arbitrary cracks is complicated due to the difficulty of creating three-dimensional models, the computing power required, and absence of closed- form solutions of the problem. Another focus of this project was performing three-dimensional contact analysis of a spiral bevel gear set incorporating cracks. These analyses were significant in determining the influence of change of tooth flexibility due to crack growth on the magnitude and location of contact loads. This is an important concern since change in contact loads might lead to differences in SIFs and therefore result in alteration of the crack trajectory. Contact analyses performed in this report showed the expected trend of decreasing tooth loads carried by the cracked tooth with increasing crack length. Decrease in tooth loads lead to differences between SIFs extracted from finite element contact analysis and finite element analysis with Hertz contact loads. This effect became more pronounced as the crack grew.

  14. Origin of cosmic rays in the spiral galaxy NGC 3310

    SciTech Connect

    Duric, N.

    1984-01-01

    The problem of cosmic ray production in the spiral galaxy NGC 3310 is addressed by analyzing and comparing optical and radio continuum data. Tentative results indicate that on global scales relativistic electrons may be produced in the shock front associated with the density wave while on local scales extreme population I objects may be producing them. It is inferred that the same conclusions apply to all cosmic rays produced in the disk. 9 references.

  15. Design principles for Bernal spirals and helices with tunable pitch

    NASA Astrophysics Data System (ADS)

    Fejer, Szilard N.; Chakrabarti, Dwaipayan; Kusumaatmaja, Halim; Wales, David J.

    2014-07-01

    Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment.Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00324a

  16. Straddle Design Of Spiral Bevel And Hypoid Gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Litvin, Faydor L.; Kuan, Chihping; Kieffer, Jonathan; Bossler, Robert

    1994-01-01

    Computer-assisted method of analysis of straddle designs for spiral bevel and hypoid gears helps prevent undercutting of gear shafts during cutting of gear teeth. Analytical method and computer program based on equations for surface traced out by motion of head cutter, equation for cylindrical surface of shaft, and equations expressing relationships among coordinate systems fixed to various components of gear-cutting machine tool and gear.

  17. Acute Atherosis of the Uterine Spiral Arteries: Clinicopathologic Implications

    PubMed Central

    Kim, Joo-Yeon; Kim, Yeon Mee

    2015-01-01

    Acute atherosis is unique vascular changes of the placenta associated with poor placentation. It is characterized by subendothelial lipid-filled foam cells, fibrinoid necrosis of the arterial wall, perivascular lymphocytic infiltration, and it is histologically similar to early-stage atherosclerosis. Acute atherosis is rare in normal pregnancies, but is frequently observed in non- transformed spiral arteries in abnormal pregnancies, such as preeclampsia, small for gestational age (SGA), fetal death, spontaneous preterm labor and preterm premature rupture of membranes. In preeclampsia, spiral arteries fail to develop physiologic transformation and retain thick walls and a narrow lumen. Failure of physiologic transformation of spiral arteries is believed to be the main cause of uteroplacental ischemia, which can lead to the production of anti-angiogenic factors and induce endothelial dysfunction and eventually predispose the pregnancy to preeclampsia. Acute atherosis is more frequently observed in the spiral arteries of the decidua of the placenta (parietalis or basalis) than in the decidual or myometrial segments of the placental bed. The presence and deeper location of acute atherosis is associated with poorer pregnancy outcomes, more severe disease, earlier onset of preeclampsia, and a greater frequency of SGA neonates in patients with preeclampsia. Moreover, the idea that the presence of acute atherosis in the placenta may increase the risk of future cardiovascular disease in women with a history of preeclampsia is of growing concern. Therefore, placental examination is crucial for retrospective investigation of pregnancy complications and outcomes, and accurate placental pathology based on universal diagnostic criteria in patients with abnormal pregnancies is essential for clinicopathologic correlation. PMID:26530045

  18. Spiral arms in scattered light images of protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Dong, Ruobing

    2015-12-01

    In the past few years, resolved observations with high angular resolution have revealed rich structures in gaseous protoplanetary disks. Among all discoveries, one of the most prominent is the giant double-spiral structure, found in MWC 758, SAO 206462, and HD 100453. The NIR images of these disks taken by Subaru/HiCIAO, VLT/NACO, and VLT/SPHERE showed two spiral arms at tens of AU from the center. The arms are very open with large pitch angles, and are in a nearly m=2 rotational symmetry. Although planets are known to be able to excite density waves in protoplanetary disks, fitting observations with linear theory of the density wave demands unreasonably big scale height in the disk, thus temperature, in order to make the arms as open as observed (and no need to mention the coincidence that they all have two nearly m=2 arms). Using 3D hydro and radiative transfer simulations, we find that a massive perturber (giant planet, brown dwarf, or stellar mass companion) can excite multiple spiral arms in the density structure, and the arms inside the perturber's orbit are very prominent in NIR scattered light images, in striking similarity with observations. Very recently, the perturber was found for the first time in the HD 100453 disk, as a M dwarf companion. This gives us great confidence of our models, and suggests that the double spirals in the other two objects, MWC 758 and SAO 206462, are very likely to be excited in a similar way, by a currently unseen perturber outside the arms. In particular, by measuring the angular distance between the two arms and comparing it with our models, we determine that the perturber in SAO 206462 is about 6 Jupiter mass.

  19. MOLECULAR GAS EVOLUTION ACROSS A SPIRAL ARM IN M51

    SciTech Connect

    Egusa, Fumi; Scoville, Nick; Koda, Jin

    2011-01-10

    We present sensitive and high angular resolution CO(1-0) data obtained by the Combined Array for Research in Millimeter-wave Astronomy observations toward the nearby grand-design spiral galaxy M51. The angular resolution of 0.''7 corresponds to 30 pc, which is similar to the typical size of giant molecular clouds (GMCs), and the sensitivity is also high enough to detect typical GMCs. Within the 1' field of view centered on a spiral arm, a number of GMC-scale structures are detected as clumps. However, only a few clumps are found to be associated with each giant molecular association (GMA) and more than 90% of the total flux is resolved out in our data. Considering the high sensitivity and resolution of our data, these results indicate that GMAs are not mere confusion with GMCs but plausibly smooth structures. In addition, we have found that the most massive clumps are located downstream of the spiral arm, which suggests that they are at a later stage of molecular cloud evolution across the arm and plausibly are cores of GMAs. By comparing with H{alpha} and Pa{alpha} images, most of these cores are found to have nearby star-forming regions. We thus propose an evolutionary scenario for the interstellar medium, in which smaller molecular clouds collide to form smooth GMAs at spiral arm regions and then star formation is triggered in the GMA cores. Our new CO data have revealed the internal structure of GMAs at GMC scales, finding the most massive substructures on the downstream side of the arm in close association with the brightest H II regions.

  20. Spiral and Rotor Patterns Produced by Fairy Ring Fungi

    NASA Astrophysics Data System (ADS)

    Karst, N.; Dralle, D.; Thompson, S. E.

    2014-12-01

    Soil fungi fill many essential ecological and biogeochemical roles, e.g. decomposing litter, redistributing nutrients, and promoting biodiversity. Fairy ring fungi offer a rare glimpse into the otherwise opaque spatiotemporal dynamics of soil fungal growth, because subsurface mycelial patterns can be inferred from observations at the soil's surface. These observations can be made directly when the fungi send up fruiting bodies (e.g., mushrooms and toadstools), or indirectly via the effect the fungi have on neighboring organisms. Grasses in particular often temporarily thrive on the nutrients liberated by the fungus, creating bands of rich, dark green turf at the edge of the fungal mat. To date, only annular (the "ring" in fairy ring) and arc patterns have been described in the literature. We report observations of novel spiral and rotor pattern formation in fairy ring fungi, as seen in publically available high-resolution aerial imagery of 22 sites across the continental United States. To explain these new behaviors, we first demonstrate that a well-known model describing fairy ring formation is equivalent to the Gray-Scott reaction-diffusion model, which is known to support a wide range of dynamical behaviors, including annular traveling waves, rotors, spirals, and stable spatial patterns including spots and stripes. Bifurcation analysis and numerical simulation are then used to define the region of parameter space that supports spiral and rotor formation. We find that this region is adjacent to one within which typical fairy rings develop. Model results suggest simple experimental procedures that could potentially induce traditional ring structures to exhibit rotor or spiral dynamics. Intriguingly, the Gray-Scott model predicts that these same procedures could be used to solicit even richer patterns, including spots and stripes, which have not yet been identified in the field.

  1. Anisotropy and spiral organizing centers in patterned excitable media.

    PubMed

    Steinbock, O; Kettunen, P; Showalter, K

    1995-09-29

    Chemical wave behavior in a patterned Belousov-Zhabotinsky system prepared by printing the catalyst of the reaction on membranes with an ink jet printer is described. Cellular inhomogeneities give rise to global anisotropy in wave propagation, with specific local patterns resulting in hexagonal, diamond, and pentagonal geometries. Spiral wave sources appear spontaneously and serve as organizing centers of the surrounding wave activity. The experimental methodology offers flexibility for studies of excitable media with made-to-order spatial inhomogeneities. PMID:17820240

  2. Dipole-on-dielectric model for infrared lithographic spiral antennas

    NASA Astrophysics Data System (ADS)

    Boreman, Glenn D.; Dogariu, Aristide; Christodoulou, Christos; Kotter, Dale

    1996-03-01

    We present a dipole-on-dielectric model for lithographic antennas used for bolometer coupling in the infrared. The predicted antenna patterns show good agreement with measurements of Au-on-Si spiral antennas at 9.5- mu m wavelength. Angle- and polarization-resolved measurements are proposed, which will further probe the behavior of these antenna structures and facilitate refinement of the analytical models.

  3. Density-tapered spiral arrays for ultrasound 3-D imaging.

    PubMed

    Ramalli, Alessandro; Boni, Enrico; Savoia, Alessandro Stuart; Tortoli, Piero

    2015-08-01

    The current high interest in 3-D ultrasound imaging is pushing the development of 2-D probes with a challenging number of active elements. The most popular approach to limit this number is the sparse array technique, which designs the array layout by means of complex optimization algorithms. These algorithms are typically constrained by a few steering conditions, and, as such, cannot guarantee uniform side-lobe performance at all angles. The performance may be improved by the ungridded extensions of the sparse array technique, but this result is achieved at the expense of a further complication of the optimization process. In this paper, a method to design the layout of large circular arrays with a limited number of elements according to Fermat's spiral seeds and spatial density modulation is proposed and shown to be suitable for application to 3-D ultrasound imaging. This deterministic, aperiodic, and balanced positioning procedure attempts to guarantee uniform performance over a wide range of steering angles. The capabilities of the method are demonstrated by simulating and comparing the performance of spiral and dense arrays. A good trade-off for small vessel imaging is found, e.g., in the 60λ spiral array with 1.0λ elements and Blackman density tapering window. Here, the grating lobe level is -16 dB, the lateral resolution is lower than 6λ the depth of field is 120λ and, the average contrast is 10.3 dB, while the sensitivity remains in a 5 dB range for a wide selection of steering angles. The simulation results may represent a reference guide to the design of spiral sparse array probes for different application fields. PMID:26285181

  4. Micro-fabricated silicon spiral spring based electromagnetic energy harvester

    NASA Astrophysics Data System (ADS)

    Bang, Dong Hyun; Park, Jae Yeong

    2013-06-01

    In this study, an electromagnetic energy harvester using a bulk micromachined silicon spiral spring and a polydimethylsiloxane (PDMS) packaging technique was fabricated and characterized to generate electrical energy from ultra-low ambient vibrations under at vibration accelerations 0.3g. The proposed energy harvester was comprised of a highly-miniaturized neodymium-ironboron (NdFeB) magnet, a silicon spiral spring, a multi-turn copper coil, and a PDMS housing in order to improve its electrical output power and reduce its size/volume. When an external vibration directly moves the mounted magnet as a seismic mass at the center of the spiral spring, the mechanical energy of the moving mass was transformed into electrical energy through the 183 turns of the solenoid copper coil. Silicon spiral springs were used to generate a high electrical output power by maximizing the deflection of the movable mass in response to low-level vibrations. The fabricated energy harvester exhibited a resonant frequency of 36 Hz and an optimal load resistance of 99 Ω. It generated an output power of 29.02 µW and load voltage of 107.3 mV at a vibration acceleration of 0.3g. It also exhibited a power density and normalized power density of 48.37 µW·cm-3 and 537.41 µW·cm-3·g-2, respectively. The total volume of the fabricated energy harvester was 1 cm × 1 cm × 0.6 cm (height).

  5. A comparison of spiral tracers in M81

    SciTech Connect

    Kaufman, M.; Bash, F.N.; Hine, B.; Rots, A.H.; Elmegreen, D.M. Texas Univ., Austin National Radio Astronomy Observatory, Socorro, NM IBM Thomas J. Watson Research Center, Yorktown Heights, NY Vassar College, Poughkeepsie, NY )

    1989-10-01

    High-resolution digitized images of M81 in H I, B and I bands, H-alpha, and the radio continuum are studied. The H I gas, the nonthermal radio emission, the dust and the narrow dust filaments, the young stars, and the giant radio H II regions are each distributed across a broad spiral compression zone that starts near the measured position of the spiral velocity shock front and extends 1-2 kpc downstream from the shock front. Old and young stars both collect near the gravitational potential minimum on the arms. The evidence favors an SNR origin for the cosmic ray electrons that produce the nonthermal radio arms. The location of an H II region above or below the midplane explains the observed dispersion in the value of the visual extinction for the set of giant radio H II regions. Many of the general features of the spiral arms can be explained by density wave models that emphasize the cloudy nature of the interstellar medium. 57 refs.

  6. Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, Yonghwi; Kim, Woong-Tae; Elmegreen, Bruce G.

    2015-08-01

    It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters β and {F}, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of β =1-∞ and {F}=5% and 10%. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression factor in the background shocks. When {F}=5% and β ≲ 10 or {F}=10% and β ∼ 5–10, the most unstable mode has a wavelength of ∼0.1–0.2 times the arm-to-arm separation, which appears consistent with a mean spacing of observed feathers.

  7. Computer experiments on the structure and dynamics of spiral galaxies

    NASA Technical Reports Server (NTRS)

    Hohl, F.

    1972-01-01

    The evolution of an initially balanced rotating disk of stars with an initial velocity dispersion given by Toomre's local criterion was investigated by means of a computer model for isolated disks of stars. It was found that the disk is unstable against very large scale modes. A stable axisymmetric disk with a velocity dispersion much larger than that given by Toomre's criterion was generated. The final mass distribution for the disk gives a high density central core and a disk population of stars that is closely approximated by an exponential variation. Various methods and rates of cooling the hot axisymmetric disks were investigated. It was found that the cooling resulted in the development of two-arm spiral structures which persisted as long as cooling continued. An experiment was performed to induce spiral structure in a galaxy by means of the close passage of a companion galaxy. Parameters similar to those expected for M51 and its companion were used. It was found that because of the high velocity dispersion of the disturbed disk galaxy, only a weak two-arm spiral structure appeared. The evolution of a uniformly rotating disk galaxy which is a stationary solution of the collisionless Boltzmann equation was investigated for various values of the initial rms velocity dispersion. It was found that the disk becomes stable at a value of the velocity dispersion predicted by theory.

  8. Fluid mechanics and heat transfer spirally fluted tubing

    NASA Astrophysics Data System (ADS)

    Larue, J. C.; Libby, P. A.; Yampolsky, J. S.

    1981-08-01

    The objective of this program is to develop both a qualitative and a quantitative understanding of the fluid mechanics and heat transfer mechanisms that underlie the measured performance of the spirally fluted tubes under development at General Atomic. The reason for the interest in the spirally fluted tubes is that results to date have indicated three advantages to this tubing concept: The fabrication technique of rolling flutes on strip and subsequently spiralling and simultaneously welding the strip to form tubing results in low fabrication costs, approximately equal to those of commercially welded tubing. The heat transfer coefficient is increased without a concomitant increase of the friction coefficient on the inside of the tube. In single-phase axial flow of water, the helical flutes continuously induce rotation of the flow both within and without the tube as a result of the effect of curvature. An increase in condensation heat transfer on the outside of the tube is achieved. In a vertical orientation with fluid condensing on the outside of the helically fluted tube, the flutes provide a channel for draining the condensed fluid.

  9. Fundamental Mass-Spin-Morphology Relation Of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Obreschkow, D.; Glazebrook, K.

    2014-03-01

    This work presents high-precision measurements of the specific baryon angular momentum j b contained in stars, atomic gas, and molecular gas, out to >~ 10 scale radii, in 16 nearby spiral galaxies of the THINGS sample. The accuracy of these measurements improves on existing studies by an order of magnitude, leading to the discovery of a strong correlation between the baryon mass M b, j b, and the bulge mass fraction β, fitted by \\beta =-(0.34+/- 0.03)\\,lg\\,(j_bM_b^{-1}/[10^{-7}\\, kpc\\,km\\,s^{-1}\\,{M}_{\\odot }^{-1}])-(0.04+/- 0.01) on the full sample range of 0 <= β <~ 0.3 and 109 M ⊙ < M b < 1011 M ⊙. The corresponding relation for the stellar quantities M * and j * is identical within the uncertainties. These M-j-β relations likely originate from the proportionality between jM -1 and the surface density of the disk that dictates its stability against (pseudo-)bulge formation. Using a cold dark matter model, we can approximately explain classical scaling relations, such as the fundamental plane of spiral galaxies, the Tully-Fisher relation, and the mass-size relation, in terms of the M-j(-β) relation. These results advocate the use of mass and angular momentum as the most fundamental quantities of spiral galaxies.

  10. Characterization of Atmospheric Ekman Spirals at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Rysman, Jean-François; Lahellec, Alain; Vignon, Etienne; Genthon, Christophe; Verrier, Sébastien

    2016-08-01

    We use wind speed and temperature measurements taken along a 45-m meteorological tower located at Dome C, Antarctica (75.06°S, 123.19°E) to highlight and characterize the Ekman spiral. Firstly, temperature records reveal that the atmospheric boundary layer at Dome C is stable during winter and summer nights (i.e., >85 % of the time). The wind vector, in both speed and direction, also shows a strong dependence with elevation. An Ekman model was then fitted to the measurements. Results show that the wind vector follows the Ekman spiral structure for more than 20 % of the year (2009). Most Ekman spirals have been detected during summer nights, that is, when the boundary layer is slightly stratified. During these episodes, the boundary-layer height ranged from 25 to 100 m, the eddy viscosity from 0.004 to 0.06 m^2 s^{-1}, and the Richardson number from zero to 1.6.

  11. Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, Yonghwi; Kim, Woong-Tae; Elmegreen, Bruce G.

    2015-08-01

    It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters β and {F}, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of β =1-∞ and {F}=5% and 10%. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression factor in the background shocks. When {F}=5% and β ≲ 10 or {F}=10% and β ˜ 5-10, the most unstable mode has a wavelength of ˜0.1-0.2 times the arm-to-arm separation, which appears consistent with a mean spacing of observed feathers.

  12. Simulating Fatigue Crack Growth in Spiral Bevel Gears

    NASA Technical Reports Server (NTRS)

    Spievak, Lisa E.; Wawrzynek, Paul A.; Ingraffea, Anthony R.

    2000-01-01

    The majority of helicopter transmission systems utilize spiral bevel gears to convert the horizontal power from the engine into vertical power for the rotor. Due to the cyclical loading on a gear's tooth, fatigue crack propagation can occur. In rotorcraft applications, a crack's trajectory determines whether the gear failure will be benign or catastrophic for the aircraft. As a result, the capability to predict crack growth in gears is significant. A spiral bevel gear's complex shape requires a three dimensional model of the geometry and cracks. The boundary element method in conjunction with linear elastic fracture mechanics theories is used to predict arbitrarily shaped three dimensional fatigue crack trajectories in a spiral bevel pinion under moving load conditions. The predictions are validated by comparison to experimental results. The sensitivity of the predictions to variations in loading conditions and crack growth rate model parameters is explored. Critical areas that must be understood in greater detail prior to predicting more accurate crack trajectories and crack growth rates in three dimensions are identified.

  13. Infrared emission and tidal interactions of spiral galaxies

    NASA Technical Reports Server (NTRS)

    Byrd, Gene G.

    1987-01-01

    Computer simulations of tidal interactions of spiral galaxies are used to attempt to understand recent discoveries about infrared (IR) emitting galaxies. It is found that the stronger tidal perturbation by a companion the more disk gas clouds are thrown into nucleus crossing orbits and the greater the velocity jumps crossing spiral arms. Both these tidally created characteristics would create more IR emission by high speed cloud collisions and more IR via effects of recently formed stars. This expectation at greater tidal perturbation matches the observation of greater IR emission for spiral galaxies with closer and/or more massive companions. The greater collision velocities found at stronger perturbations on the models will also result in higher dust temperature in the colliding clouds. In the IR pairs examined, most have only one member, the larger, detected and when both are detected, the larger is always the more luminous. In simulations and in a simple analytic description of the strong distance dependence of the tidal force, it is found that the big galaxy of a pair is more strongly affected than the small.

  14. Spiral and Rotor Patterns Produced by Fairy Ring Fungi.

    PubMed

    Karst, Nathaniel; Dralle, David; Thompson, Sally

    2016-01-01

    A broad class of soil fungi form the annular patterns known as 'fairy rings' and provide one of the only means to observe spatio-temporal dynamics of otherwise cryptic fungal growth processes in natural environments. We present observations of novel spiral and rotor patterns produced by fairy ring fungi and explain these behaviors mathematically by first showing that a well known model of fairy ring fungal growth and the Gray-Scott reaction-diffusion model are mathematically equivalent. We then use bifurcation analysis and numerical simulations to identify the conditions under which spiral waves and rotors can arise. We demonstrate that the region of dimensionless parameter space supporting these more complex dynamics is adjacent to that which produces the more familiar fairy rings, and identify experimental manipulations to test the transitions between these spatial modes. These same manipulations could also feasibly induce fungal colonies to transition from rotor/spiral formation to a set of richer, as yet unobserved, spatial patterns. PMID:26934477

  15. Spiral and Rotor Patterns Produced by Fairy Ring Fungi

    PubMed Central

    2016-01-01

    A broad class of soil fungi form the annular patterns known as ‘fairy rings’ and provide one of the only means to observe spatio-temporal dynamics of otherwise cryptic fungal growth processes in natural environments. We present observations of novel spiral and rotor patterns produced by fairy ring fungi and explain these behaviors mathematically by first showing that a well known model of fairy ring fungal growth and the Gray-Scott reaction-diffusion model are mathematically equivalent. We then use bifurcation analysis and numerical simulations to identify the conditions under which spiral waves and rotors can arise. We demonstrate that the region of dimensionless parameter space supporting these more complex dynamics is adjacent to that which produces the more familiar fairy rings, and identify experimental manipulations to test the transitions between these spatial modes. These same manipulations could also feasibly induce fungal colonies to transition from rotor/spiral formation to a set of richer, as yet unobserved, spatial patterns. PMID:26934477

  16. Ultra-precision turning of complex spiral optical delay line

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaodong; Li, Po; Fang, Fengzhou; Wang, Qichang

    2011-11-01

    Optical delay line (ODL) implements the vertical or depth scanning of optical coherence tomography, which is the most important factor affecting the scanning resolution and speed. The spinning spiral mirror is found as an excellent optical delay device because of the high-speed and high-repetition-rate. However, it is one difficult task to machine the mirror due to the special shape and precision requirement. In this paper, the spiral mirror with titled parabolic generatrix is proposed, and the ultra-precision turning method is studied for its machining using the spiral mathematic model. Another type of ODL with the segmental shape is also introduced and machined to make rotation balance for the mass equalization when scanning. The efficiency improvement is considered in details, including the rough cutting with the 5- axis milling machine, the machining coordinates unification, and the selection of layer direction in turning. The onmachine measuring method based on stylus gauge is designed to analyze the shape deviation. The air bearing is used as the measuring staff and the laser interferometer sensor as the position sensor, whose repeatability accuracy is proved up to 10nm and the stable feature keeps well. With this method developed, the complex mirror with nanometric finish of 10.7nm in Ra and the form error within 1um are achieved.

  17. Star formation rates of spiral galaxies in the Cosmic Web

    NASA Astrophysics Data System (ADS)

    Alpaslan, Mehmet; Marcum, Pamela M.; Galaxy And Mass Assembly (GAMA)

    2016-01-01

    We look for shifts in stellar mass and star formation rate along filaments in the cosmic web by examining the stellar masses and UV-derived star formation rates of 1,799 ungrouped and unpaired spiral galaxies from the Galaxy And Mass Assembly (GAMA) survey that reside in filaments. We devise multiple distance metrics to characterise the complex geometry of filaments, and find that galaxies closer to the orthogonal core of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. We also find that these peripheral galaxies have higher specific star formations at a given mass. Our results suggest a model in which gas accretion from voids onto filaments is primarily in an orthogonal direction. While the star formation rates of spiral galaxies in filaments are susceptible to their locations, we find that the global star formation rates of galaxies in different large scale environments are similar to each other. The primary discriminant in star formation rates is therefore the stellar mass of each spiral galaxy, as opposed to its large scale environment.

  18. Lasing spiral and square-shaped optical microcavities

    NASA Astrophysics Data System (ADS)

    Chern, Grace D.

    Optical microcavities, which confine light to small dimensions by total internal reflection (TIR), possess unique characteristics that depend on its morphology. The following dissertation presents experimental results from two-dimensional optical microcavities of various cross-sectional shapes. This includes a novel design, specifically a spiral-shaped InGaN multiple-quantum well microcavity, which is the first known microdisk device to produce unidirectional lasing emission from a single output beam when selectively optically-excited with a ring-shaped beam. The spiral microcavities also perform successfully under pulsed as well as continuous-wave current-injection conditions. Furthermore, the output intensity of the spiral microlaser is shown to increase with the addition of semicircle-based microdisks, which serve as optical amplifiers. Square-shaped dye-doped polymer micro-pillars are also examined which could be useful as add/drop filters for wavelength-division-multiplexing. Lasing emission is detected from the square corners due to completely TIR-confined modes which correspond to ray orbits with an incident angle theta inc at or near 45°. Additionally, surprising strong emission from the sidewalls is observed, which is associated with modes that are only partially TIR-confined but still have a high enough reflection coefficient to be sustained.

  19. Automated Quantification of Arbitrary Arm-Segment Structure in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Davis, Darren Robert

    This thesis describes a system that, given approximately-centered images of spiral galaxies, produces quantitative descriptions of spiral galaxy structure without the need for per-image human input. This structure information consists of a list of spiral arm segments, each associated with a fitted logarithmic spiral arc and a pixel region. This list-of-arcs representation allows description of arbitrary spiral galaxy structure: the arms do not need to be symmetric, may have forks or bends, and, more generally, may be arranged in any manner with a consistent spiral-pattern center (non-merging galaxies have a sufficiently well-defined center). Such flexibility is important in order to accommodate the myriad structure variations observed in spiral galaxies. From the arcs produced from our method it is possible to calculate measures of spiral galaxy structure such as winding direction, winding tightness, arm counts, asymmetry, or other values of interest (including user-defined measures). In addition to providing information about the spiral arm "skeleton" of each galaxy, our method can enable analyses of brightness within individual spiral arms, since we provide the pixel regions associated with each spiral arm segment. For winding direction, arm tightness, and arm count, comparable information is available (to various extents) from previous efforts; to the extent that such information is available, we find strong correspondence with our output. We also characterize the changes to (and invariances in) our output as a function of modifications to important algorithm parameters. By enabling generation of extensive data about spiral galaxy structure from large-scale sky surveys, our method will enable new discoveries and tests regarding the nature of galaxies and the universe, and will facilitate subsequent work to automatically fit detailed brightness models of spiral galaxies.

  20. Estimation of the galactic spiral pattern speed from Cepheids

    NASA Astrophysics Data System (ADS)

    Bobylev, V. V.; Bajkova, A. T.

    2012-10-01

    To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with propermotions from the Hipparcos catalog and line-of-sight velocities from various sources. First, based on the entire sample of 185 stars and taking R 0 = 8 kpc, we have found the components of the peculiar solar velocity ( u ⊙, v ⊙) = (7.6, 11.6) ± (0.8, 1.1) km s-1, the angular velocity of Galactic rotation Ω0 = 27.5 ± 0.5 km s-1 kpc-1 and its derivatives Ω'0 = -4.12 ± 0.10 km s-1 kpc-2 and Ω″0 = 0.85 ± 0.07 km s-1 kpc-3, the amplitudes of the velocity perturbations in the spiral density wave f R = -6.8 ± 0.7 and f θ = 3.3 ± 0.5 km s-1, the pitch angle of a two-armed spiral pattern ( m = 2) i = -4.6° ± 0.1° (which corresponds to a wavelength λ = 2.0 ± 0.1 kpc), and the phase of the Sun in the spiral density wave χ⊙ = -193° ± 5°. The phase χ⊙ has been found to change noticeably with the mean age of the sample. Having analyzed these phase shifts, we have determined the mean value of the angular velocity difference Ω p - Ω, which depends significantly on the calibrations used to estimate the individual ages of Cepheids. When estimating the ages of Cepheids based on Efremov's calibration, we have found |Ω p - Ω0| = 10 ± 1stat ± 3syst km s-1 kpc-1. The ratio of the radial component of the gravitational force produced by the spiral arms to the total gravitational force of the Galaxy has been estimated to be f r0 = 0.04 ± 0.01.

  1. SU-E-I-26: The CT Compatibility of a Novel Direction Modulated Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer

    SciTech Connect

    Elzibak, A; Safigholi, H; Soliman, A; Ravi, A; Song, WY; Kager, P; Han, D

    2015-06-15

    Purpose: To examine CT metal image artifact from a novel direction-modulated brachytherapy (DMBT) tandem applicator (95% tungsten) for cervical cancer using a commercially available orthopedic metal artifact reduction (O-MAR) algorithm. Comparison to a conventional stainless steel applicator is also performed. Methods: Each applicator was placed in a water-filled phantom resembling the female pelvis and scanned in a Philips Brilliance 16-slice CT scanner using two pelvis protocols: a typical clinical protocol (120kVp, 16×0.75mm collimation, 0.692 pitch, 1.0s rotation, 350mm field of view (FOV), 600mAs, 1.5mm slices) and a protocol with a higher kVp and mAs setting useful for larger patients (140kVp, 16×0.75mm collimation, 0.688 pitch, 1.5s rotation, 350mm FOV, 870mAs, 1.5mm slices). Images of each tandem were acquired with and without the application of the O-MAR algorithm. Baseline scans of the phantom (no applicator) were also collected. CT numbers were quantified at distances from 5 to 30 mm away from the applicator’s edge (in increments of 5mm) using measurements at eight angles around the applicator, on three consecutive slices. Results: While the presence of both applicators degraded image quality, the DMBT applicator resulted in larger streaking artifacts and dark areas in the image compared to the stainless steel applicator. Application of the O-MAR algorithm improved all acquired images, both visually and quantitatively. The use of low and high kVp and mAs settings (120 kVp/600mAs and 140 kVp/870mAs) in conjunction with the O-MAR algorithm lead to similar CT numbers in the vicinity of the applicator and a similar reduction of the induced metal artifact. Conclusion: This work indicated that metal artifacts induced by the DMBT and the stainless steel applicator are greatly reduced when using the O-MAR algorithm, leading to better quality phantom images. The use of a high dose protocol provided similar improvements in metal artifacts compared to the

  2. Head CT scan in Iranian minor head injury patients: evaluating current decision rules.

    PubMed

    Sadegh, Robab; Karimialavijeh, Ehsan; Shirani, Farzaneh; Payandemehr, Pooya; Bahramimotlagh, Hooman; Ramezani, Mahtab

    2016-02-01

    The objective of this study is to select one of the seven available clinical decision rules for minor head injury, for managing Iranian patients. This was a prospective cohort study evaluating medium- or high-risk minor head injury patients presenting to the Emergency Department. Patients with minor head trauma who were eligible for brain imaging based on seven available clinical decision rules (National Institute for Health and Clinical Excellence (NICE), National Emergency X-Radiography Utilization Study (NEXUS)-II, Neurotraumatology Committee of the World Federation of Neurosurgical Societies (NCWFNS), New Orleans, American College of Emergency Physicians (ACEP) Guideline, Scandinavian, and Canadian computed tomography (CT) head rule) were selected. Subjects were underwent a non-contrast axial spiral head CT scan. The outcome was defined as abnormal and normal head CT scan. Univariate analysis and stepwise linear regression were applied to show the best combination of risk factors for detecting CT scan abnormalities. Five hundred patients with minor head trauma were underwent brain CT scan. The following criteria were derived by stepwise linear regression: Glasgow Coma Scale (GCS) less than 15, confusion, signs of basal skull fracture, drug history of warfarin, vomiting more than once, loss of consciousness, focal neurologic deficit, and age over 65 years. This model has 86.15 % (75.33-93.45 %) sensitivity and 46.44 % (46.67-51.25 %) specificity in detecting minor head injury patients with CT scan abnormalities (95 % confidence interval). Of seven decision rules, only the Canadian CT Head Rule possesses seven of the eight high-risk factors associated with abnormal head CT results which were identified by this study. This study underlines the Canadian CT Head Rule's utility in Iranian minor head injury patients. Our study encourages researchers to evaluate available guidelines in different communities. PMID:26407978

  3. Your Radiologist Explains CT Colonography

    MedlinePlus Videos and Cool Tools

    ... About this Site RadiologyInfo.org is produced by: Image/Video Gallery Your Radiologist Explains CT Colonography (Virtual ... to allow for inflation with air while CT images are being taken. If you’re scheduled for ...

  4. Beaming photons with spin and orbital angular momentum via a dipole-coupled plasmonic spiral antenna.

    PubMed

    Rui, Guanghao; Nelson, Robert L; Zhan, Qiwen

    2012-08-13

    We analytically and numerically study the emission properties of an electric dipole coupled to a plasmonic spiral structure with different pitch. As a transmitting antenna, the spiral structure couples the radiation from the electric dipole into circularly polarized emitted photons in the far field. The spin carried by the emitted photons is determined by the handedness of the spiral antenna. By increasing the spiral pitch in the unit of surface plasmon wavelength, these circularly polarized photons also gain orbital angular momentum with different topological charges. This phenomenon is attributed to the presence of a geometric phase arising from the interaction of light from point source with the anisotropic spiral structure. The circularly polarized vortex emission from such optically coupled spiral antenna also has high directivity, which may find important applications in quantum optical information, single molecule sensing, and integrated photonic circuits. PMID:23038521

  5. Pelvic CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. ... weight limit. Too much weight can damage the scanner's working parts. You will be asked to remove ...

  6. A comparative study of feed impedances of a circular and three different spiral antenna arrays

    NASA Astrophysics Data System (ADS)

    Ramachandra, V.; Dey, K. K.; Khastgir, P.

    1982-08-01

    Mathematical derivation of feed impedances of the dipole radiators of a circular and three different spiral arrays has been made for both constant and progressive phase distributions. A set of graphs, which show the variations of these impedances and their components from radiator to radiator, has been obtained. Spiral distributions of impedances can be observed on the Argand diagram in the cases of the three spiral arrays.

  7. Toroidal spiral Nambu-Goto strings around higher-dimensional black holes

    SciTech Connect

    Igata, Takahisa; Ishihara, Hideki

    2010-08-15

    We present solutions of the Nambu-Goto equation for test strings in a shape of toroidal spiral in five-dimensional spacetimes. In particular, we show that stationary toroidal spirals exist around the five-dimensional Myers-Perry black holes. We also show the existence of innermost stationary toroidal spirals around the five-dimensional black holes like geodesic particles orbiting around four-dimensional black holes.

  8. PET/CT imaging artifacts.

    PubMed

    Sureshbabu, Waheeda; Mawlawi, Osama

    2005-09-01

    The purpose of this paper is to introduce the principles of PET/CT imaging and describe the artifacts associated with it. PET/CT is a new imaging modality that integrates functional (PET) and structural (CT) information into a single scanning session, allowing excellent fusion of the PET and CT images and thus improving lesion localization and interpretation accuracy. Moreover, the CT data can also be used for attenuation correction, ultimately leading to high patient throughput. These combined advantages have rendered PET/CT a preferred imaging modality over dedicated PET. Although PET/CT imaging offers many advantages, this dual-modality imaging also poses some challenges. CT-based attenuation correction can induce artifacts and quantitative errors that can affect the PET emission images. For instance, the use of contrast medium and the presence of metallic implants can be associated with focal radiotracer uptake. Furthermore, the patient's breathing can introduce mismatches between the CT attenuation map and the PET emission data, and the discrepancy between the CT and PET fields of view can lead to truncation artifacts. After reading this article, the technologist should be able to describe the principles of PET/CT imaging, identify at least 3 types of image artifacts, and describe the differences between PET/CT artifacts of different causes: metallic implants, respiratory motion, contrast medium, and truncation. PMID:16145223

  9. Seventh-generation CT

    NASA Astrophysics Data System (ADS)

    Besson, G. M.

    2016-03-01

    A new dual-drum CT system architecture has been recently introduced with the potential to achieve significantly higher temporal resolution than is currently possible in medical imaging CT. The concept relies only on known technologies; in particular rotation speeds several times higher than what is possible today could be achieved leveraging typical x-ray tube designs and capabilities. However, the architecture lends itself to the development of a new arrangement of x-ray sources in a toroidal vacuum envelope containing a rotating cathode ring and a (optionally rotating) shared anode ring to potentially obtain increased individual beam power as well as increase total exposure per rotation. The new x-ray source sub-system design builds on previously described concepts and could make the provision of multiple conventional high-power cathodes in a CT system practical by distributing the anode target between the cathodes. In particular, relying on known magnetic-levitation technologies, it is in principle possible to more than double the relative speed of the electron-beam with respect to the target, thus potentially leading to significant individual beam power increases as compared to today's state-of-the-art. In one embodiment, the proposed design can be naturally leveraged by the dual-drum CT concept previously described to alleviate the problem of arranging a number of conventional rotating anode-stem x-ray tubes and power conditioners on the limited space of a CT gantry. In another embodiment, a system with three cathodes is suggested leveraging the architecture previously proposed by Franke.

  10. Single-shot phase imaging with randomized light (SPIRaL).

    PubMed

    Horisaki, Ryoichi; Egami, Riki; Tanida, Jun

    2016-02-22

    We present a method for single-shot phase imaging with randomized light (SPIRaL). In SPIRaL, the complex (amplitude and phase) field of an object illuminated with a randomized coherent beam is captured with an image sensor, without the need for any reference light. The object field is retrieved from the single captured intensity image by a compressive sensing-based algorithm with a sparsity constraint. SPIRaL has higher observation speed, light efficiency, and flexibility of the implementation compared with previous methods. We demonstrate SPIRaL numerically and experimentally. PMID:26907032

  11. Standing spin waves and solitons in a quasi-one-dimensional spiral structure

    SciTech Connect

    Kiselev, V. V. Raskovalov, A. A.

    2013-02-15

    On the basis of the sine-Gordon model, we calculated the absorption spectrum for the external pump power in a quasi-one-dimensional spiral structure of easy-plane magnets without the inversion center in the presence of a static magnetic field perpendicular to the magnetic spiral axis. It is shown that these data can be used for determining the material constants of the magnet and diagnostics of spin waves and solitons in its spiral structure. The possibility of using magnetooptical methods to observe local translations of the spiral structure during formation and motion of solitons in it is discussed.

  12. Competition between traveling fluid waves of left and right spiral vortices and their different amplitude combinations.

    PubMed

    Pinter, A; Lücke, M; Hoffmann, Ch

    2006-02-01

    Stability, bifurcation properties, and the spatiotemporal behavior of different nonlinear combination structures of spiral vortices in the counterrotating Taylor-Couette system are investigated by full numerical simulations and by coupled amplitude-equation approximations. Stable cross-spiral structures with continuously varying content of left- and right-spiral modes are found. They provide a stability transferring connection between the initially stable, axially counterpropagating wave states of pure spirals and the axially standing waves of so-called ribbons that become stable slightly farther away from the onset of vortex flow. PMID:16486832

  13. Spectral, diffusive and convective properties of fractal and spiral fields

    NASA Astrophysics Data System (ADS)

    Angilella, J. R.; Vassilicos, J. C.

    1998-12-01

    Spectral, diffusive and convective properties of one-dimensional pulse fields displaying a well-defined Kolmogorov capacity D ε [0, 1] are investigated. The energy spectrum of fractal or spiral alternating pulse fields scales as k D. The energy spectrum of homogeneous fractal non-alternating pulse fields scales as k -D. Both these scaling laws hold in a range of wavenumbers between η -1 and L-1, where η is the smallest distance between pulses and L (≫ η) is a characteristic large scale of the structure. The space-filling geometry, which is quantified by the Kolmogorov capacity D, makes the field less autocorrelated (more singular) in the alternating case, whereas it makes it more autocorrelated (less singular) in the non-alternating case. Significant quantitative differences between the spectral properties of homogeneous fractals and of spirals exist. The energy spectrum of a spiral non-alternating pulse field scales as k-1 between x-1N and L-1, where x N ∼ η( L/η) D ≫ η characterizes the inhomogeneity of the structure. The spectrum is flat outside this wavenumber range. When submitted to the action of molecular diffusion (molecular diffusivity v) the energy of these fields decays as follows. Energy decay is accelerated in the case of fractal or spiral alternating pulse fields: E(t) (for{ηv≪t≪L/v and is delayed (“trapped”) in the case of non-alternating homogeneous fractal pulse fields: E(t) ( forη/v≪t≪L/v This energy trapping manifests itself in a different manner in the case of spiral non-alternating pulse fields. In this case energy decays only logarithmically for η 2/ v ≪ t ≪ x2N/ v, then decays like t-1/2 for longer times. When submitted to the combined action of convection and diffusion (Burgers equation) the energy of these fields of N pulses each of integral m ≫ v decays as follows. It is independent of D in the case of alternating pulse fields, and is delayed in the case of non-alternating pulse fields. For homogeneous

  14. Stellar populations in spiral galaxies: broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    2006-06-01

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  15. Stellar populations in spiral galaxies: Broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  16. Preoperative evaluation of stage T3, central-type non-small cell lung cancer with double sleeve lobectomy under complete video-assisted thoracoscopic surgery using spiral computed tomography post-processing techniques

    PubMed Central

    Guan, Yubao; Huang, Jun; Xia, Tingting; You, Xiaoting; He, Jiaxi

    2016-01-01

    Background To investigate the estimated value of spiral computed tomography (CT) post-processing techniques in preoperative stage T3, central-type non-small cell lung cancer (NSCLC) with double sleeve lobectomy under complete video-assisted thoracoscopic surgery (c-VATS). Methods Preoperative clinical date and CT reconstructed data of 10 patients who underwent double sleeve lobectomy with upper lobe stage T3, central-type NSCLC were retrospectively analysed and compared to surgical pathological results and cross-sectional CT data. The diagnostic criterions of tumour invasion of pulmonary artery and bronchus were divided into five grades, which included estimation of upper lobe pulmonary arteries and bronchi (40 branches, respectively). Results The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of cross-sectional CT images of pulmonary artery tumour invasion were 78.57%, 58.33%, 81.48%, 53.85%, and 72.50%, respectively, while the respective values for CT reconstructed images were 93.55%, 87.50%, 96.67%, 70.00%, and 90.00%, showing statistical significance (χ2=4.021, P=0.045). Similarly, the evaluate, the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of cross-sectional CT images of bronchial tumour invasion were 82.76%, 45.45%, 80.00%, 50.00%, and 72.50%, respectively, while the respective values for CT reconstructed images were 97.06%, 66.67%, 94.29%, 80.00%, 92.50%; these results were also statistically significant (χ2=5.541, P=0.019). Conclusions The sensitivity, specificity, and diagnostic accuracy of the spiral CT post-processing techniques were better than cross-sectional CT images in estimating the extent of tumour invasion in the pulmonary arteries and bronchi of central-type NSCLC. CT post-processing techniques are essential tools in preoperative examination and operative method selection of central-type lung cancer with double sleeve

  17. Post cyclone spiral eddy in the Bay of Bengal.

    NASA Astrophysics Data System (ADS)

    Srinivasa Rao, N.; Rao, K. H.; Ramana, I. V.; Rao, M. V.; Anjaneyuluy, Y.

    Bay of Bengal is a semi enclosed tropical ocean basin that is highly influenced by monsoonal winds and receives large volumes of fresh water from both river discharge and rainfall Bay of Bengal experiences southwest monsoon during June -- September and Northeast monsoon during November to February This is a region which experiences right from depression to super cyclone Rainfall and fresh river water discharge the upper layers leading to the formation the strong stratified surface layer and there by restricting the turbulent wind driven mixing Prasanna kumar et al 2002 We identified the formation of spiral eddy diameter 300 Km after the passage of Tropical Super Cyclone 05B 25 Oct -- 30 Oct 1999 in the Bay of Bengal Spiral eddy of high Chlorophyll is observed in the chlorophyll image derived from IRS-P4 OCM Satellite data At location where the maximum wind speed was 140 Knots cyclone induced circular currents sustained for 3 weeks after passage of cyclone which were responsible for formation of the spiral eddy Surprisingly phytoplankton chlorophyll-a bloom was not seen along the cyclone track as earlier studies revealed Fuentes-Yaco et al 1997 Nayak et al 2001 Subrahmanyam et al 2002 Zedler et al 2002 Lin et al 2003 McKinnon et al 2003 Vinaychandran and Mathew 2003 Babin et al 2004 The reason could be the strong stratified layer 60 m present in the central BOB But we observed chlorophyll-a bloom near the coast where less wind speeds 35 Knots were present This could be because of shallow 10 m

  18. STAR FORMATION IN THE OUTER DISK OF SPIRAL GALAXIES

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Cote, Stephanie; Schade, David E-mail: vanzee@astro.indiana.edu E-mail: David.Schade@nrc-cnrc.gc.ca

    2012-09-20

    We combine new deep and wide field of view H{alpha} imaging of a sample of eight nearby (d Almost-Equal-To 17 Mpc) spiral galaxies with new and archival H I and CO imaging to study the star formation and the star formation regulation in the outer disk. We find that, in agreement with previous studies, star formation in the outer disk has low covering fractions, and star formation is typically organized into spiral arms. The star formation in the outer disk is at extremely low levels, with typical star formation rate surface densities of {approx}10{sup -5} to 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}. We find that the ratio of the radial extent of detected H II regions to the radius of the H I disk is typically {approx}>85%. This implies that in order to further our understanding of the implications of extended star formation, we must further our understanding of the formation of extended H I disks. We measure the gravitational stability of the gas disk, and find that the outer gaseous disk is typically a factor of {approx}2 times more stable than the inner star-forming disk. We measure the surface density of outer disk H I arms, and find that the disk is closer to gravitational instability along these arms. Therefore, it seems that spiral arms are a necessary, but not sufficient, requirement for star formation in the outer disk. We use an estimation of the flaring of the outer gas disk to illustrate the effect of flaring on the Schmidt power-law index; we find that including flaring increases the agreement between the power-law indices of the inner and outer disks.

  19. An Optical Search For Supernova Remnants in Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Matonick, D. M.; Fesen, R. A.; Blair, W. P.; Long, K. S.

    1994-12-01

    Imaging with narrow-band Hα , [S II], and red continuum filters has been used to distinguish supernova remnant (SNR) candidates from photoionized nebulae in seven nearby spiral galaxies: NGC 2403, NGC 3031 (M81), NGC 5194 (M51), NGC 5204, NGC 5457 (M101), NGC 5585, and NGC 6946. Nebulae which show [S II]/Hα > 0.45, indicating shock-heated emission, are identified as SNR candidates. The number of SNRs found in each galaxy using this technique is 3 in NGC 5204, 5 in NGC 5585, 30 in NGC 2403, 32 in M81, 35 in NGC 6946, and 112 in M101. Spectra of some of the emission nebulae have also been obtained, and were used to confirm SNR identifications. Because of its comparatively high radial velocity, M51 could not be examined adequately with our filter set; however, one bright SNR was found and spectroscopically confirmed. In NGC 2403, we obtained spectra on remnant candidates 1 and 2 of D'Odorico et al. (1980, A&AS, 40, 67), and confirmed them to be SNRs. We also detect the optical SNR identified by Blair & Fesen (1994, ApJ, 424, L103) in NGC 6946, and find an optical SNR counterpart to the X-ray source S2 identified by Schlegel (1994, ApJ, 424, L99). Sizes of observed SNRs range from unresolved (< 50 pc) to over 300x150 pc for one object in NGC 5585. Although our search technique limits our detection of SNRs embedded in bright H II regions, in the galaxies with clearly defined spiral arms (i.e NGC 6946, M81, M101), most SNRs appear to trace the spiral arms. Analysis of luminosity functions, diameters, abundances, and distributions of the samples of SNRs will also be discussed.

  20. Turbulence and Star Formation in a Sample of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Maier, Erin R.; Hunter, Deidre Ann; Chien, Li-Hsin

    2016-01-01

    We investigate turbulent gas motions in spiral galaxies and their importance to star formation in far outer disks, where the column density is typically far below the critical value for spontaneous gravitational collapse. Following the methods of Burkhart et al. (2010) as applied to the Small Magellanic Cloud, we use the third and fourth statistical moments, skewness and kurtosis, which are indicators of structures caused by turbulence, to examine the integrated neutral hydrogen (Hι) column density of a sample of spiral galaxies selected from The Hι Nearby Galaxy Survey (THINGS, Walter et al. 2008). We examine the kurtosis and skewness values of each galaxy as a whole, as well as their variation as a function of radius and in discrete sub-regions defined by a square, moving 'kernel,' essentially splitting each galaxy into a grid. We then create individual grid maps of kurtosis and skewness for each galaxy. To investigate the relation between these moments and star formation, we compare these maps with maps of each galaxy's far-ultraviolet (FUV) image, taken by the Galaxy Evolution Explorer (GALEX) satellite. We find that the moments are largely uniform across the galaxies: the variation does not appear to trace any star forming regions. This may, however, be due to the spatial resolution of our analysis, which could potentially limit the scale of turbulent motions to at most ~700 pc. From our analysis of the comparison between the two moments themselves, we find that the gas motions in our sample galaxies are largely supersonic. This analysis shows that Burkhart et al. (2010)'s methods may be applied not just to dwarf galaxies but normal spiral galaxies as well.We acknowledge the NSF for their funding of this work through their Research Experience for Undergraduates (REU) program (Grant No. AST-1461200).

  1. Fundamental mass-spin-morphology relation of spiral galaxies

    SciTech Connect

    Obreschkow, D.; Glazebrook, K.

    2014-03-20

    This work presents high-precision measurements of the specific baryon angular momentum j {sub b} contained in stars, atomic gas, and molecular gas, out to ≳ 10 scale radii, in 16 nearby spiral galaxies of the THINGS sample. The accuracy of these measurements improves on existing studies by an order of magnitude, leading to the discovery of a strong correlation between the baryon mass M {sub b}, j {sub b}, and the bulge mass fraction β, fitted by β=−(0.34±0.03) lg (j{sub b}M{sub b}{sup −1}/[10{sup −7} kpc km s{sup −1} M{sub ⊙}{sup −1}])−(0.04±0.01) on the full sample range of 0 ≤ β ≲ 0.3 and 10{sup 9} M {sub ☉} < M {sub b} < 10{sup 11} M {sub ☉}. The corresponding relation for the stellar quantities M {sub *} and j {sub *} is identical within the uncertainties. These M-j-β relations likely originate from the proportionality between jM {sup –1} and the surface density of the disk that dictates its stability against (pseudo-)bulge formation. Using a cold dark matter model, we can approximately explain classical scaling relations, such as the fundamental plane of spiral galaxies, the Tully-Fisher relation, and the mass-size relation, in terms of the M-j(-β) relation. These results advocate the use of mass and angular momentum as the most fundamental quantities of spiral galaxies.

  2. The opacity of spiral disks from counts of distant galaxies.

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Gonzalez, R. A.; Allen, R. J.; van der Kruit, P. C.

    2004-12-01

    The numbers of distant galaxies seen in an HST image of a spiral galaxy is an indication of the average extinction by dust in the disk. This number of distant galaxies has to be calibrated for crowding effects and for this the ``Synthetic Field Method'' (SFM, Gonzalez et al. 1998) was developed. Synthetic fields are the science field with a dimmed Hubble Deep Field added. From the relation between the dimming and the number of synthetic galaxies, the average extinction in the science field can be derived. 32 HST/WFPC2 fields were analysed and from the numbers of distant galaxies an average radial extinction profile for spiral disks was constructed, for the whole sample, arm and disk regions and different Hubble types. When the average radial extinction profile is compared to the HI surface density profile, an estimate of the average gas-to-dust ratio as a function of radius can be obtained. The effects of the phase of the hydrogen and metallicity gradient in disks are discussed. The average radial extinction profile is compared to the light distribution of spiral disks. The relation between typical radii of light and dust and the relation between surface brightness and extinction is also explored. Combining the detailed images of dust emission from the Spitzer space telescope with the extinction measurements from counts in HST images could offer insight into the relative prominence of cold dust and possibly the dust geometry in the disk. Future work on dust extinction using the wealth of new imaging in the HST archive is briefly discussed. This research was supported by funding from STSCI, the Director's Discretionary Research Fund and the Kapteyn Institute.

  3. Iron emission line from the spiral galaxy M 101

    NASA Astrophysics Data System (ADS)

    Yamauchi, Shigeo

    2016-06-01

    Archival Suzaku data of the face-on spiral galaxy M 101 were analyzed. An intense emission line at 6.72^{+0.10}_{-0.12}keV was detected in the central region. This line is identified with a K-line from He-like iron, which indicates the existence of a thin thermal plasma with a temperature of several keV. The iron line luminosity within the central 5'-radius region is estimated to be (2-12) × 1037 erg s-1. The origin of the iron emission line is discussed.

  4. Kinematic Mass Measurements of Inner and Outer Spiral Disks

    NASA Astrophysics Data System (ADS)

    Herrmann, Kimberly A.; Ciardullo, R.

    2010-01-01

    Our knowledge of the structure and kinematics of galactic disks and halos is quite limited. While integrated light spectroscopy has provided a large amount of information on inner disks, once outside 2.5 disk scale lengths, almost nothing is known. Does the mass-to-light ratio (M/L) stay constant in the outer regions? Does the stellar scale height stay constant or do disks flare? Are galactic disks really maximal and could there be any trends with Hubble type? Are dark matter halos fit better by NFW or pseudo-isothermal models? We have been using planetary nebulae (PNe) to probe the kinematic structure of face-on spiral disks by identifying large ( 100) samples of these objects via narrow-band imaging, and then measuring their radial velocities with follow-up, high-precision ( 5 km/s) spectroscopy. Our results for IC 342, M74, M83, M94, and M101 are quite interesting. With one exception (M101) the z-velocity dispersion (sigmaz) of galactic disks declines exponentially with the light out to 3 disk scale lengths. This is exactly as expected for a constant M/L, constant scale height disk. However, in the two galaxies with significant data past this radius, the values of sigmaz asymptote out at 20 km/s. Moreover, our analysis finds kinematic evidence for significant flaring in the outer regions, especially in M94. These observations are in excellent agreement with predictions derived from models of disk heating by halo substructure, and demonstrate how kinematic surveys in the outer disks of spirals can be used to test hierarchical models of galaxy formation. We also find that the disks of late-type galaxies are far from maximal, that the disks of early type spirals have higher M/L ratios than the disks of later-type objects, and that the unseen inner halos of spiral galaxies are better fit by pseudo-isothermal laws than by NFW models.

  5. Optical induction scheme for assembling nondiffracting aperiodic Vogel spirals

    SciTech Connect

    Diebel, Falko Rose, Patrick; Boguslawski, Martin; Denz, Cornelia

    2014-05-12

    We introduce an experimental approach to realize aperiodic photonic lattices based on multiplexing of nondiffracting Bessel beams. This holographic optical induction scheme takes advantage of the well localized Bessel beam as a basis to assemble two-dimensional photonic lattices. We present the realization of an optically induced two-dimensional golden-angle Vogel spiral lattice, which belongs to the family of deterministic aperiodic structures. With our technique, a very broad class of photonic refractive index landscapes now becomes accessible to optical induction, which could not be realized with established distributed holographic techniques.

  6. Unstable spiral modes in disk-shaped galaxies

    PubMed Central

    Lau, Y. Y.; Lin, C. C.; Mark, James W.-K.

    1976-01-01

    The mechanisms for the maintenance and the excitation of trailing spiral modes of density waves in diskshaped galaxies, as proposed by Lin in 1969 and by Mark recently, are substantiated by an analysis of the gas-dynamical model of the galaxy. The self-excitation of the unstable mode in caused by waves propagating outwards from the corotation circle, which carry away angular momentum of a sign opposite to that contained in the wave system inside that circle. Specifically, a simple dispersion relationship is given as a definite integral, which allows the immediate determination of the pattern frequency and the amplification rate, once the basic galactic model is known. PMID:16592313

  7. Spatial analysis of IRAS observations of nearby spirals

    NASA Technical Reports Server (NTRS)

    Ball, Roger; Lo, R. Y.

    1990-01-01

    The unbiased survey of the infrared sky carried out by the Infrared Astronomy Satellite (IRAS) satellite has greatly accelerated advances in understanding the dust component of our own and external galaxies. However, most extragalactic studies to date have been based on the IRAS Point Source Catalog (PSC), which has two serious limitations. First, in sources where a significant fraction of the flux is extended, significant errors may result from using PSC fluxes in comparative studies, and these errors could be systematic if the tendency to be non-pointlike depends on physical properties of the galaxy. Additionally, use of PSC fluxes rules out any direct investigation of the spatial distribution of the IRAS emission from disks in external galaxies. Since work on the Galactic IRAS results has shown that very different physical processes can make varying contributions to the observed flux, it is important to look at a wide sample of galaxies with some spatial resolution to study the relative dominance of these processes under a variety of conditions. Here, researchers report on work they are doing to carry out this program for many nearby spirals, using an analysis package that was developed for this purpose. Researchers carried out analysis for a sample of 121 nearby spirals. The fraction of the flux contained in a point source varies from 0 to 1 across the sample, all of which are well resolved at their nominal optical diameters. There is no evidence that the galaxies of smaller angular size are less likely to be resolved by IRAS at this level. The program gives results which are quite repeatable from scan to scan; the fraction f (point source flux over total flux) at 60 microns has typical errors of 0.03 when different scans are combined. Approximately two-thirds of the sample have more flux in the extended than in the nuclear component. There is a tendency for earlier-type spirals to be less centrally concentrated, but this effect is slight and the degree of

  8. The Spiral Wave of Our Galaxy Near Inner Lindblad Resonance

    PubMed Central

    Mark, James W-K.

    1971-01-01

    The dispersion relationship for short-wavelength spiral density waves in our Galaxy has been refined to remove the divergences that occurred in wave number and in amplitude as inner Lindblad resonance is approached. The wave is found to be evanescent in an annular region near 4 kpc. By 3 kpc, the inward propagating trailing wave is completely absorbed. The outgoing leading wave is suppressed compared to the trailing one because it begins in the evanescent state. Throughout this region of inner Lindblad resonance, a smooth wave amplitude has been obtained, and it has a sharp peak correlating well with the observed density of ionized hydrogen. PMID:16591941

  9. On the origin and history of stars in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Hernández, David M.; Macció, Andrea V.; van den Bosch, Frank C.

    2010-10-01

    The formation of spiral galaxies is an important topic of debate in astrophysics. We use smooth-particle hydrodynamic (SPH) simulations to follow the formation, in a fully ΛCDM cosmological context, of two disk galaxies similar, in mass, to our Milky Way. Using the dynamics of the star particles we are able to identify three distinct components in the stellar budget of our galaxies: a thin disk, a thick disk and a spheroid. We make a detailed analysis of where and when stars in the three different components come about. Our study can help create a more consistent picture of how galaxies similar to our own form.

  10. Optical induction scheme for assembling nondiffracting aperiodic Vogel spirals

    NASA Astrophysics Data System (ADS)

    Diebel, Falko; Rose, Patrick; Boguslawski, Martin; Denz, Cornelia

    2014-05-01

    We introduce an experimental approach to realize aperiodic photonic lattices based on multiplexing of nondiffracting Bessel beams. This holographic optical induction scheme takes advantage of the well localized Bessel beam as a basis to assemble two-dimensional photonic lattices. We present the realization of an optically induced two-dimensional golden-angle Vogel spiral lattice, which belongs to the family of deterministic aperiodic structures. With our technique, a very broad class of photonic refractive index landscapes now becomes accessible to optical induction, which could not be realized with established distributed holographic techniques.

  11. Tooth contact shift in loaded spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Savage, M.; Altidis, P. C.; Lewicki, D. G.; Coy, J. J.; Litvin, F. L.

    1989-01-01

    An analytical method is presented to predict the shifts of the contact ellipses of spiral bevel gear teeth under load. The contact ellipse shift is the motion of the tooth contact position from the ideal pitch point to its location under load. The shifts are due to the elastic motions of the gear and pinion supporting shafts and bearings. The calculations include the elastic deflections of the gear shafts and the deflections of the four shaft bearings. The method assumes that the surface curvature of each tooth is constant near the unloaded pitch point. Results from these calculations will help designers reduce transmission weight without seriously reducing transmission performance.

  12. Tooth Contact Shift in Loaded Spiral Bevel Gears

    NASA Technical Reports Server (NTRS)

    Savage, M.; Altidis, P. C.; Lewicki, D. G.; Coy, J. J.; Litvin, F. L.

    1989-01-01

    An analytical method is presented to predict the shifts of the contact ellipses of spiral bevel gear teeth under load. The contact ellipse shift is the motion of the tooth contact position from the ideal pitch point to its location under load. The shifts are due to the elastic motions of the gear and pinion supporting shafts and bearings. The calculations include the elastic deflections of the gear shafts and the deflections of the four shaft bearings. The method assumes that the surface curvature of each tooth is constant near the unloaded pitch point. Results from these calculations will help designers reduce transmission weight without seriously reducing transmission performance.

  13. The relation between infrared and radio emission in spiral galaxies

    NASA Technical Reports Server (NTRS)

    Helou, George

    1991-01-01

    A remarkable correlation between the far infrared and the radio continuum emission of star forming galaxies was one of the early results based on IRAS data, and has remained one of the most intriguing. Recent work has extended the correlation to early type galaxies, revealing a slightly different ratio in lenticulars. When radio and infrared maps of disk galaxies are compared, the radio disks appear systematically more diffuse. This has been interpreted as a manifestation of the diffusion of cosmic-ray electrons, and has allowed a fresh look at the behavior of magnetic fields and cosmic rays in spiral galaxies, and at their relation to the rest of the interstellar medium.

  14. Gain degradation and efficiencies of spiral electron multipliers

    NASA Technical Reports Server (NTRS)

    Judge, R. J. R.; Palmer, D. A.

    1973-01-01

    The characteristics of spiral electron multipliers as functions of accumulated counts were investigated. The mean gain of the multipliers showed a steady decline from about 100 million when new, to about one million after 100 billion events when biased in a saturation mode. For prolonged use in a space environment, improved life expectancy might be obtained with a varying bias voltage adjusted to maintain the gain comfortably above a given discrimination level. Pulse-height distributions at various stages of the lifetime and variations of efficiency with energy of detected electrons are presented.

  15. Finite difference time domain modeling of spiral antennas

    NASA Technical Reports Server (NTRS)

    Penney, Christopher W.; Beggs, John H.; Luebbers, Raymond J.

    1992-01-01

    The objectives outlined in the original proposal for this project were to create a well-documented computer analysis model based on the finite-difference, time-domain (FDTD) method that would be capable of computing antenna impedance, far-zone radiation patterns, and radar cross-section (RCS). The ability to model a variety of penetrable materials in addition to conductors is also desired. The spiral antennas under study by this project meet these requirements since they are constructed of slots cut into conducting surfaces which are backed by dielectric materials.

  16. Evolution of Field Spiral Galaxies up to Redshifts z = 1

    NASA Astrophysics Data System (ADS)

    Böhm, Asmus; Ziegler, Bodo L.

    2007-10-01

    We have gained intermediate-resolution spectroscopy with the FORS instruments of the Very Large Telescope (VLT) and high-resolution imaging with the Advanced Camera for Surveys aboard HST for a sample of 220 distant field spiral galaxies within the FORS Deep Field and William Herschel Deep Field. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric and observational effects, such as blurring due to the slit width and seeing influence. Using these fits, the maximum rotation velocity Vmax could be determined for 124 galaxies that cover the redshift range 0.1spirals to very late types and irregulars. The luminosity-rotation velocity distribution of this sample, which represents an average look-back time of ~5 Gyr, is offset from the Tully-Fisher relation (TFR) of local low-mass spirals, whereas the distant high-mass spirals are compatible with the local TFR. Taking the magnitude-limited character of our sample into account, we show that the slope of the local and the intermediate- z TFR would be in compliance if its scatter decreased by more than a factor of 3 between z~0.5 and 0. Accepting this large evolution of the TFR scatter, we hence find no strong evidence for a mass- or luminosity-dependent evolution of disk galaxies. On the other hand, we derive stellar mass-to-luminosity ratios (M/L) that indicate a luminosity-dependent evolution in the sense that distant low-luminosity disks have much lower M/L than their local counterparts, while high-luminosity disks barely evolved in M/L over the covered redshift range. This could be the manifestation of the ``downsizing'' effect, i.e., the successive shift of the peak of star formation from high-mass to low-mass galaxies toward lower redshifts. This trend might be canceled out in the TF diagram due to the simultaneous evolution of multiple parameters. We also estimate the ratios

  17. Concha bullosa: CT evaluation.

    PubMed

    Zinreich, S J; Mattox, D E; Kennedy, D W; Chisholm, H L; Diffley, D M; Rosenbaum, A E

    1988-01-01

    Aeration of the middle turbinate, termed "concha bullosa," is a common anatomical variant of intranasal anatomy. Of 320 patients evaluated for sinus disease with coronal CT, 34% had concha bullosa on at least one side. The overall incidence of inflammatory disease in the ostiomeatal complex in these symptomatic patients was not different between those with and without concha bullosa. However, there were many cases in which an abnormally large middle turbinate appeared to obstruct the ostiomeatal complex causing secondary infection of the ethmoid, frontal, and maxillary sinuses. Obstruction of drainage of the concha bullosa itself can lead to mucocele formation. Furthermore, the presence of a concha bullosa has important implications for the technique of endoscopic surgery used in the management of the sinus disease. The anatomy, pathophysiology, and CT findings in patients with concha bullosa are reviewed. PMID:3170840

  18. Signal displacement in spiral-in acquisitions: simulations and implications for imaging in SFG regions.

    PubMed

    Brewer, Kimberly D; Rioux, James A; Klassen, Martyn; Bowen, Chris V; Beyea, Steven D

    2012-07-01

    Susceptibility field gradients (SFGs) cause problems for functional magnetic resonance imaging (fMRI) in regions like the orbital frontal lobes, leading to signal loss and image artifacts (signal displacement and "pile-up"). Pulse sequences with spiral-in k-space trajectories are often used when acquiring fMRI in SFG regions such as inferior/medial temporal cortex because it is believed that they have improved signal recovery and decreased signal displacement properties. Previously postulated theories explain differing reasons why spiral-in appears to perform better than spiral-out; however it is clear that multiple mechanisms are occurring in parallel. This study explores differences in spiral-in and spiral-out images using human and phantom empirical data, as well as simulations consistent with the phantom model. Using image simulations, the displacement of signal was characterized using point spread functions (PSFs) and target maps, the latter of which are conceptually inverse PSFs describing which spatial locations contribute signal to a particular voxel. The magnitude of both PSFs and target maps was found to be identical for spiral-out and spiral-in acquisitions, with signal in target maps being displaced from distant regions in both cases. However, differences in the phase of the signal displacement patterns that consequently lead to changes in the intervoxel phase coherence were found to be a significant mechanism explaining differences between the spiral sequences. The results demonstrate that spiral-in trajectories do preserve more total signal in SFG regions than spiral-out; however, spiral-in does not in fact exhibit decreased signal displacement. Given that this signal can be displaced by significant distances, its recovery may not be preferable for all fMRI applications. PMID:22503093

  19. Digitalized accurate modeling of SPCB with multi-spiral surface based on CPC algorithm

    NASA Astrophysics Data System (ADS)

    Huang, Yanhua; Gu, Lizhi

    2015-09-01

    The main methods of the existing multi-spiral surface geometry modeling include spatial analytic geometry algorithms, graphical method, interpolation and approximation algorithms. However, there are some shortcomings in these modeling methods, such as large amount of calculation, complex process, visible errors, and so on. The above methods have, to some extent, restricted the design and manufacture of the premium and high-precision products with spiral surface considerably. This paper introduces the concepts of the spatially parallel coupling with multi-spiral surface and spatially parallel coupling body. The typical geometry and topological features of each spiral surface forming the multi-spiral surface body are determined, by using the extraction principle of datum point cluster, the algorithm of coupling point cluster by removing singular point, and the "spatially parallel coupling" principle based on the non-uniform B-spline for each spiral surface. The orientation and quantitative relationships of datum point cluster and coupling point cluster in Euclidean space are determined accurately and in digital description and expression, coupling coalescence of the surfaces with multi-coupling point clusters under the Pro/E environment. The digitally accurate modeling of spatially parallel coupling body with multi-spiral surface is realized. The smooth and fairing processing is done to the three-blade end-milling cutter's end section area by applying the principle of spatially parallel coupling with multi-spiral surface, and the alternative entity model is processed in the four axis machining center after the end mill is disposed. And the algorithm is verified and then applied effectively to the transition area among the multi-spiral surface. The proposed model and algorithms may be used in design and manufacture of the multi-spiral surface body products, as well as in solving essentially the problems of considerable modeling errors in computer graphics and

  20. Quantitative micro-CT

    NASA Astrophysics Data System (ADS)

    Prevrhal, Sven

    2005-09-01

    Micro-CT for bone structural analysis has progressed from an in-vitro laboratory technique to devices for in-vivo assessment of small animals and the peripheral human skeleton. Currently, topological parameters of bone architecture are the primary goals of analysis. Additional measurement of the density or degree of mineralization (DMB) of trabecular and cortical bone at the microscopic level is desirable to study effects of disease and treatment progress. This information is not commonly extracted because of the challenges of accurate measurement and calibration at the tissue level. To assess the accuracy of micro-CT DMB measurements in a realistic but controlled situation, we prepared bone-mimicking watery solutions at concentrations of 100 to 600 mg/cm3 K2PO4H and scanned them with micro-CT, both in glass vials and microcapillary tubes with inner diameters of 50, 100 and 150 μm to simulate trabecular thickness. Values of the linear attenuation coefficients μ in the reconstructed image are commonly affected by beam hardening effects for larger samples and by partial volume effects for small volumes. We implemented an iterative reconstruction technique to reduce beam hardening. Partial voluming was sought to be reduced by excluding voxels near the tube wall. With these two measures, improvement on the constancy of the reconstructed voxel values and linearity with solution concentration could be observed to over 90% accuracy. However, since the expected change in real bone is small more measurements are needed to confirm that micro-CT can indeed be adapted to assess bone mineralization at the tissue level.