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Sample records for arterial transit time

  1. Noninvasive pulse transit time measurement for arterial stiffness monitoring in microgravity.

    PubMed

    McCall, Corey; Rostosky, Rea; Wiard, Richard M; Inan, Omer T; Giovangrandi, Laurent; Cuttino, Charles Marsh; Kovacs, Gregory T A

    2015-08-01

    The use of a noninvasive hemodynamic monitor to estimate arterial stiffness, by measurement of pulse transit time (PTT), was demonstrated in microgravity. The monitor's utility for space applications was shown by establishing the correlation between ground-based and microgravity-based measurements. The system consists of a scale-based ballistocardiogram (BCG) and a toe-mounted photoplethysmogram (PPG). PTT was measured from the BCG I-wave to the intersecting tangents of the first trough and maximum first derivative of the PPG waveforms of each subject. The system was tested on a recent series of parabolic flights in which the PTT of nine subjects was measured on the ground and in microgravity. An average of 60.2 ms PTT increase from ground to microgravity environments was shown, and was consistent across all test subjects (standard deviation = 32.9 ms). This increase in PTT could be explained by a number of factors associated with microgravity and reported in previous research, including elimination of hydrostatic pressure, reduction of intrathoracic pressure, and reduction of mean arterial pressure induced by vasodilation. PMID:26737764

  2. Continuous blood pressure measurement using the pulse transit time: Comparison to intra-arterial measurement.

    PubMed

    Patzak, Andreas; Mendoza, Yuri; Gesche, Heiko; Konermann, Martin

    2015-01-01

    Continuous blood pressure (BP) measurement allows the investigation of transient changes in BP and thus may give insights into mechanisms of BP control. We validated a continuous, non-invasive BP measurement based on the pulse transit time (PTT), i.e., BP(PTT), by comparing it with the intra-arterial BP (BP(i.a.)) measurement. Twelve subjects (five females and seven males) were included. BP(i.a.) was obtained from the radial artery using a system from ReCor Medical. Systolic and diastolic BP were calculated using the PTT (BP(PTT), SOMNOscreen). (PTT) was determined from the electrocardiogram and the peripheral pulse wave. The BP was modulated by application of increasing doses of dobutamine (5, 10, 20 μg/kg body mass). Systolic BP(PTT) and systolic BP(i.a.) correlated significantly (R = 0.94). The limits of agreement in the Bland-Altman plot were ± 19 mmHg; the mean values differed by 1 mmHg. The correlation coefficient for the diastolic BP measurements was R = 0.42. The limits of agreement in the Bland-Altman plot were ± 18 mmHg, with a mean difference of 5 mmHg in favour of the BP(PTT). The study demonstrates a significant correlation between the measurement methods for systolic BP. The results encourage the application of PTT-based BP measurement for the evaluation of BP dynamics and pathological BP changes. PMID:25857601

  3. 3D GRASE pulsed arterial spin labeling at multiple inflow times in patients with long arterial transit times: comparison with dynamic susceptibility-weighted contrast-enhanced MRI at 3 Tesla

    PubMed Central

    Martin, Steve Z; Madai, Vince I; von Samson-Himmelstjerna, Federico C; Mutke, Matthias A; Bauer, Miriam; Herzig, Cornelius X; Hetzer, Stefan; Günther, Matthias; Sobesky, Jan

    2015-01-01

    Pulsed arterial spin labeling (PASL) at multiple inflow times (multi-TIs) is advantageous for the measurement of brain perfusion in patients with long arterial transit times (ATTs) as in steno-occlusive disease, because bolus-arrival-time can be measured and blood flow measurements can be corrected accordingly. Owing to its increased signal-to-noise ratio, a combination with a three-dimensional gradient and spin echo (GRASE) readout allows acquiring a sufficient number of multi-TIs within a clinically feasible acquisition time of 5 minutes. We compared this technique with the clinical standard dynamic susceptibility-weighted contrast-enhanced imaging–magnetic resonance imaging in patients with unilateral stenosis >70% of the internal carotid or middle cerebral artery (MCA) at 3 Tesla. We performed qualitative (assessment by three expert raters) and quantitative (region of interest (ROI)/volume of interest (VOI) based) comparisons. In 43 patients, multi-TI PASL-GRASE showed perfusion alterations with moderate accuracy in the qualitative analysis. Quantitatively, moderate correlation coefficients were found for the MCA territory (ROI based: r=0.52, VOI based: r=0.48). In the anterior cerebral artery (ACA) territory, a readout related right-sided susceptibility artifact impaired correlation (ROI based: r=0.29, VOI based: r=0.34). Arterial transit delay artifacts were found only in 12% of patients. In conclusion, multi-TI PASL-GRASE can correct for arterial transit delay in patients with long ATTs. These results are promising for the transfer of ASL to the clinical practice. PMID:25407272

  4. SU-D-18C-05: Variable Bolus Arterial Spin Labeling MRI for Accurate Cerebral Blood Flow and Arterial Transit Time Mapping

    SciTech Connect

    Johnston, M; Jung, Y

    2014-06-01

    Purpose: Arterial spin labeling (ASL) is an MRI perfusion imaging method from which quantitative cerebral blood flow (CBF) maps can be calculated. Acquisition with variable post-labeling delays (PLD) and variable TRs allows for arterial transit time (ATT) mapping and leads to more accurate CBF quantification with a scan time saving of 48%. In addition, T1 and M0 maps can be obtained without a separate scan. In order to accurately estimate ATT and T1 of brain tissue from the ASL data, variable labeling durations were invented, entitled variable-bolus ASL. Methods: All images were collected on a healthy subject with a 3T Siemens Skyra scanner. Variable-bolus Psuedo-continuous ASL (PCASL) images were collected with 7 TI times ranging 100-4300ms in increments of 700ms with TR ranging 1000-5200ms. All boluses were 1600ms when the TI allowed, otherwise the bolus duration was 100ms shorter than the TI. All TI times were interleaved to reduce sensitivity to motion. Voxel-wise T1 and M0 maps were estimated using a linear least squares fitting routine from the average singal from each TI time. Then pairwise subtraction of each label/control pair and averaging for each TI time was performed. CBF and ATT maps were created using the standard model by Buxton et al. with a nonlinear fitting routine using the T1 tissue map. Results: CBF maps insensitive to ATT were produced along with ATT maps. Both maps show patterns and averages consistent with literature. The T1 map also shows typical T1 contrast. Conclusion: It has been demonstrated that variablebolus ASL produces CBF maps free from the errors due to ATT and tissue T1 variations and provides M0, T1, and ATT maps which have potential utility. This is accomplished with a single scan in a feasible scan time (under 6 minutes) with low sensivity to motion.

  5. Transit Timing Variations

    NASA Video Gallery

    The animation shows the difference between planet transit timing of single and multiple planet system. In tightly packed planetary systems, the gravitational pull of the planets among themselves ca...

  6. Capillary Transit Time Heterogeneity Is Associated with Modified Rankin Scale Score at Discharge in Patients with Bilateral High Grade Internal Carotid Artery Stenosis

    PubMed Central

    Mundiyanapurath, Sibu; Ringleb, Peter Arthur; Diatschuk, Sascha; Hansen, Mikkel Bo; Mouridsen, Kim; Østergaard, Leif; Wick, Wolfgang; Bendszus, Martin; Radbruch, Alexander

    2016-01-01

    Background and Purpose Perfusion weighted imaging (PWI) is inherently unreliable in patients with severe perfusion abnormalities. We compared the diagnostic accuracy of a novel index of microvascular flow-patterns, so-called capillary transit time heterogeneity (CTH) to that of the commonly used delay parameter Tmax in patients with bilateral high grade internal carotid artery stenosis (ICAS). Methods Consecutive patients with bilateral ICAS ≥ 70%NASCET who underwent PWI were retrospectively examined. Maps of CTH and Tmax were analyzed with a volumetric approach using several thresholds. Predictors of favorable outcome (modified Rankin scale at discharge 0–2) were identified using univariate and receiver operating characteristic (ROC) curve analysis. Results Eighteen patients were included. CTH ≥ 30s differentiated best between patients with favorable and unfavorable outcome when both hemispheres were taken into account (sensitivity 83%, specificity 73%, area under the curve [AUC] 0.833 [confidence interval (CI) 0.635; 1.000]; p = 0.027). The best discrimination using Tmax was achieved with a threshold of ≥ 4s (sensitivity 83%, specificity 64%, AUC 0.803 [CI 0.585;1.000]; p = 0.044). The highest AUC was found for left sided volume with CTH ≥ 15s (sensitivity 83%, specificity 91%, AUC 0.924 [CI 0.791;1.000]; p = 0.005). Conclusion The study suggests that CTH is superior to Tmax in discriminating ICAS patients with favorable from non-favorable outcome. This finding may reflect the simultaneous involvement of large vessels and microvessels in ICAS and underscore the need to diagnose and manage both aspects of the disease. PMID:27336668

  7. Children and Transition Time.

    ERIC Educational Resources Information Center

    Baker, Betty Ruth

    Daily transitions in early childhood centers and classrooms include periods when children are completing one activity, preparing to begin a new activity, and moving from place to place in a room or building. Transition activities involve teaching techniques that prepare learners to listen, relax, sit down, move between locations or activities, and…

  8. Arterial Transit Time Mapping Obtained by Pulsed Continuous 3D ASL Imaging with Multiple Post-Label Delay Acquisitions: Comparative Study with PET-CBF in Patients with Chronic Occlusive Cerebrovascular Disease

    PubMed Central

    Tsujikawa, Tetsuya; Kimura, Hirohiko; Matsuda, Tsuyoshi; Fujiwara, Yasuhiro; Isozaki, Makoto; Kikuta, Ken-ichiro; Okazawa, Hidehiko

    2016-01-01

    Arterial transit time (ATT) is most crucial for measuring absolute cerebral blood flow (CBF) by arterial spin labeling (ASL), a noninvasive magnetic resonance (MR) perfusion assessment technique, in patients with chronic occlusive cerebrovascular disease. We validated ASL-CBF and ASL-ATT maps calculated by pulsed continuous ASL (pCASL) with multiple post-label delay acquisitions in patients with occlusive cerebrovascular disease. Fifteen patients underwent MR scans, including pCASL, and positron emission tomography (PET) scans with 15O-water to obtain PET-CBF. MR acquisitions with different post-label delays (1.0, 1.5, 2.0, 2.5 and 3.0 sec) were also obtained for ATT correction. The theoretical framework of 2-compartmental model (2CM) was also used for the delay compensation. ASL-CBF and ASL-ATT were calculated based on the proposed 2CM, and the effect on the CBF values and the ATT correction characteristics were discussed. Linear regression analyses were performed both on pixel-by-pixel and region-of-interest bases in the middle cerebral artery (MCA) territory. There were significant correlations between ASL-CBF and PET-CBF both for voxel values (r = 0.74 ± 0.08, slope: 0.87 ± 0.22, intercept: 6.1 ± 4.9) and for the MCA territorial comparison in both affected (R2 = 0.67, y = 0.83x + 6.3) and contralateral sides (R2 = 0.66, y = 0.74x + 6.3). ASL-ATTs in the affected side were significantly longer than those in the contralateral side (1.51 ± 0.41 sec and 1.12 ± 0.30 sec, respectively, p <0.0005). CBF measurement using pCASL with delay compensation was feasible and fairly accurate even in altered hemodynamic states. PMID:27275779

  9. Linear-time transitive orientation

    SciTech Connect

    McConnell, R.M.; Spinrad, J.P.

    1997-06-01

    The transitive orientation problem is the problem of assigning a direction to each edge of a graph so that the resulting digraph is transitive. A graph is a comparability graph if such an assignment is possible. We describe an O(n + m) algorithm for the transitive orientation problem, where n and m are the number of vertices and edges of the graph; full details are given in. This gives linear time bounds for maximum clique and minimum vertex coloring on comparability graphs, recognition of two-dimensional partial orders, permutation graphs, cointerval graphs, and triangulated comparability graphs, and other combinatorial problems on comparability graphs and their complements.

  10. Time Resolved MRA: Evaluation of Intrapulmonary Circulation Parameters in Pulmonary Arterial Hypertension

    PubMed Central

    Jeong, Hyun J.; Vakil, Parmede; Sheehan, John J.; Shah, Sanjiv J.; Cuttica, Michael; Carr, James C.; Carroll, Timothy J.; Davarpanah, Amir

    2010-01-01

    Purpose To determine whether pulmonary arterial and venous transit times measured by time-resolved MRA can be used as a diagnostic tool for pulmonary arterial hypertension (PAH). Materials and Methods 12 patients with confirmed PAH and 10 healthy volunteers were scanned with IRB approval. Time-resolved MRA and 2D phase contrast flow images of the pulmonary vasculature were acquired. Pulmonary arterial and venous transit times (PaTT and PvTT) and pulmonary valve flow (PVF) were obtained. Pulmonary arterial and pulmonary venous blood volumes (PaBV and PvBV) were calculated as the product of flow and transit time. Results Patients with PAH showed statistically significant increases in PaTT and PvTT (p<0.0004, p<0.05 respectively) compared to controls. PaBV (165.2 ± 92.0ml) was significantly higher in PAH subjects than controls (97.0 ± 47.1 ml) (p<0.04), whereas PvBV (127.9 ± 148.9ml) of PAH subjects had no significant increase from those of healthy controls (142.5 ± 104.1 ml) (p<0.38). Conclusion Pulmonary arterial transit times measured using time-resolved MRA can be used as a simple, non-invasive metric for detection of altered hemodynamics in PAH. PMID:21182144

  11. On transit time instability in liquid jets

    NASA Technical Reports Server (NTRS)

    Grabitz, G.; Meier, G.

    1982-01-01

    A basic transit time instability in flows with disturbances of speed is found. It was shown that the mass distribution is established by and large by the described transit time effects. These transit time effects may also be involved for gas jets.

  12. NO TRANSIT TIMING VARIATIONS IN WASP-4

    SciTech Connect

    Petrucci, R.; Schwartz, M.; Buccino, A. P.; Mauas, P. J. D.; Jofré, E.; Cúneo, V.; Gómez, M.; Martínez, C.

    2013-12-20

    We present six new transits of the system WASP-4. Together with 28 light curves published in the literature, we perform a homogeneous study of its parameters and search for variations in the transits' central times. The final values agree with those previously reported, except for a slightly lower inclination. We find no significant long-term variations in i or R{sub P} /R {sub *}. The O-C mid-transit times do not show signs of transit timing variations greater than 54 s.

  13. Magnetic transit-time flowmeter

    DOEpatents

    Forster, George A.

    1976-07-06

    The flow rate of a conducting fluid in a stream is determined by disposing two permanent-magnet flowmeters in the stream, one downstream of the other. Flow of the conducting fluid causes the generation of both d-c and a-c electrical signals, the a-c comprising flow noise. Measurement of the time delay between similarities in the a-c signals by cross-correlation methods provides a measure of the rate of flow of the fluid.

  14. Venous pulse transit time in normal pregnancy and preeclampsia.

    PubMed

    Tomsin, Kathleen; Mesens, Tinne; Molenberghs, Geert; Gyselaers, Wilfried

    2012-04-01

    Uncomplicated pregnancies (n = 16) were evaluated longitudinally and compared to early- (n = 12) and late-onset (n = 14) preeclampsia patients, assessed once at diagnosis. Pulse transit time (PTT), equivalent to pulse wave velocity, was measured as the time interval between corresponding characteristics of electrocardiography and Doppler waves, corrected for heart rate, at the level of renal interlobar veins, hepatic veins, and arcuate branches of uterine arteries. Impedance cardiography was used to measure PTT at the level of the thoracic aorta. In normal pregnancy, all PTT increased gradually (P ≤ .01). Pulse transit time was shorter in late-onset preeclampsia (P < .05) and also in early-onset preeclampsia, with exception for hepatic veins and thoracic aorta (P > .05). Our results indicate that PTT is an easy and highly accessible measure for vascular reactivity at both arterial and venous sites of the circulation. Our observations correlate well with known gestational cardiovascular adaptation mechanisms. This suggests that PTT could be used as a new parameter in the evaluation and prediction of preeclampsia. PMID:22378859

  15. Arterial pressure transfer characteristics: effects of travel time.

    PubMed

    Westerhof, Berend E; Guelen, Ilja; Stok, Wim J; Wesseling, Karel H; Spaan, Jos A E; Westerhof, Nico; Bos, Willem Jan; Stergiopulos, Nikos

    2007-02-01

    We investigated the quantitative contribution of all local conduit arterial, blood, and distal load properties to the pressure transfer function from brachial artery to aorta. The model was based on anatomical data, Young's modulus, wall viscosity, blood viscosity, and blood density. A three-element windkessel represented the distal arterial tree. Sensitivity analysis was performed in terms of frequency and magnitude of the peak of the transfer function and in terms of systolic, diastolic, and pulse pressure in the aorta. The root mean square error (RMSE) described the accuracy in wave-shape prediction. The percent change of these variables for a 25% alteration of each of the model parameters was calculated. Vessel length and diameter are found to be the most important parameters determining pressure transfer. Systolic and diastolic pressure changed <3% and RMSE <1.8 mmHg for a 25% change in vessel length and diameter. To investigate how arterial tapering influences the pressure transfer, a single uniform lossless tube was modeled. This simplification introduced only small errors in systolic and diastolic pressures (1% and 0%, respectively), and wave shape was less well described (RMSE, approximately 2.1 mmHg). Local (arm) vasodilation affects the transfer function little, because it has limited effect on the reflection coefficient. Since vessel length and diameter translate into travel time, this parameter can describe the transfer accurately. We suggest that with a, preferably, noninvasively measured travel time, an accurate individualized description of pressure transfer can be obtained. PMID:16963619

  16. The Rapid Initiation, Titration, and Transition from Intravenous to Oral Treprostinil in a Patient with Severe Pulmonary Arterial Hypertension

    PubMed Central

    Gleason, James Benjamin; Dolan, Justin; Piran, Pirouz; Rahaghi, Franck Farzad

    2015-01-01

    In patients who require urgent initiation of pulmonary arterial hypertension medications due to disease progression, it is customary to start intravenous prostacyclin therapy, typically during a hospital admission. If there are complicating factors or relative contraindications to intravenous and subcutaneous prostanoids, oral treprostinil provides another pathway to prostanoid therapy, but this usually requires a prolonged titration. We describe the case of a thirty-six-year-old male with severe pulmonary arterial hypertension and contraindication to intravenous and subcutaneous prostanoid therapy due to congenital deafness and the risk of not hearing the intravenous pump alarms. Intravenous treprostinil was initiated, titrated to high dose, and then rapidly transitioned to oral treprostinil. A rapid initiation, titration, and transition from intravenous to oral treprostinil can be safely performed under watchful supervision in order to achieve higher and more efficacious doses of oral treprostinil in a timely manner. PMID:26457220

  17. Numerical analysis of the effect of turbulence transition on the hemodynamic parameters in human coronary arteries

    PubMed Central

    Gawandalkar, Udhav Ulhas; Kini, Girish; Buradi, Abdulrajak; Araki, Tadashi; Ikeda, Nobutaka; Nicolaides, Andrew; Laird, John R.; Saba, Luca; Suri, Jasjit S.

    2016-01-01

    Background Local hemodynamics plays an important role in atherogenesis and the progression of coronary atherosclerosis disease (CAD). The primary biological effect due to blood turbulence is the change in wall shear stress (WSS) on the endothelial cell membrane, while the local oscillatory nature of the blood flow affects the physiological changes in the coronary artery. In coronary arteries, the blood flow Reynolds number ranges from few tens to several hundreds and hence it is generally assumed to be laminar while calculating the WSS calculations. However, the pulsatile blood flow through coronary arteries under stenotic condition could result in transition from laminar to turbulent flow condition. Methods In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-ω model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected. Results Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated. Conclusions Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis. PMID:27280084

  18. Relationship of Intraoperative Transit Time Flowmetry Findings to Angiographic Graft Patency at Follow-Up.

    PubMed

    Amin, Sanaz; Pinho-Gomes, Ana-Catarina; Taggart, David P

    2016-05-01

    Early and late graft occlusion remains a significant complication of coronary artery bypass grafting. Transit time flowmetry is the most commonly used imaging technique to assess graft patency intraoperatively. Although the value of transit time flowmetry for intraoperative quality control of coronary anastomosis is well established, its standard variables for predicting eventual graft failure remain controversial. This review readdresses the issue of intraoperative transit time flowmetry, with a particular emphasis on defining cutoff values for standard variables and correlating them with the ability to predict midterm and long-term graft patency for arterial and venous conduits. Further research is warranted to support clinically useful recommendations on the intraoperative application and interpretation of transit time flowmetry. PMID:26876343

  19. Pulse transit time differential measurement by fiber Bragg grating pulse recorder

    NASA Astrophysics Data System (ADS)

    Umesh, Sharath; Padma, Srivani; Ambastha, Shikha; Kalegowda, Anand; Asokan, Sundarrajan

    2015-05-01

    The present study reports a noninvasive technique for the measurement of the pulse transit time differential (PTTD) from the pulse pressure waveforms obtained at the carotid artery and radial artery using fiber Bragg grating pulse recorders (FBGPR). PTTD is defined as the time difference between the arrivals of a pulse pressure waveform at the carotid and radial arterial sites. The PTTD is investigated as an indicator of variation in the systolic blood pressure. The results are validated against blood pressure variation obtained from a Mindray Patient Monitor. Furthermore, the pulse wave velocity computed from the obtained PTTD is compared with the pulse wave velocity obtained from the color Doppler ultrasound system and is found to be in good agreement. The major advantage of the PTTD measurement via FBGPRs is that the data acquisition system employed can simultaneously acquire pulse pressure waveforms from both FBGPRs placed at carotid and radial arterial sites with a single time scale, which eliminates time synchronization complexity.

  20. Late-time cosmological phase transitions

    NASA Technical Reports Server (NTRS)

    Schramm, David N.

    1991-01-01

    It is shown that the potential galaxy formation and large scale structure problems of objects existing at high redshifts (Z approx. greater than 5), structures existing on scales of 100 M pc as well as velocity flows on such scales, and minimal microwave anisotropies ((Delta)T/T) (approx. less than 10(exp -5)) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random Gaussian fluctuations and/or topological defects can form. Scale lengths of approx. 100 M pc for large scale structure as well as approx. 1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.

  1. Late-time cosmological phase transitions

    SciTech Connect

    Schramm, D.N. Fermi National Accelerator Lab., Batavia, IL )

    1990-11-01

    It is shown that the potential galaxy formation and large-scale structure problems of objects existing at high redshifts (Z {approx gt} 5), structures existing on scales of 100M pc as well as velocity flows on such scales, and minimal microwave anisotropies ({Delta}T/T) {approx lt} 10{sup {minus}5} can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random gaussian fluctuations and/or topological defects can form. Scale lengths of {approximately}100M pc for large-scale structure as well as {approximately}1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition. 47 refs., 2 figs.

  2. Real-time vascular mechanosensation through ex vivo artery perfusion

    PubMed Central

    2014-01-01

    Background Cell-based perfusion studies have provided great insight into fluid-sensing mechanisms, such as primary cilia in the renal and vascular systems. However, the intrinsic limitations of in vitro cell culture, such as the inability to reflect cellular organization within tissues, has distanced observed paradigms from possible clinical developments. Here we describe a protocol that applies ex vivo artery perfusion and calcium imaging to observe real-time cellular responses to fluid-shear stress. Results Through our ex vivo artery perfusion method, we were able to simulate physiological flow and initiate distinct fluid shear stress mechanosensory responses, as well as induced acetylcholine responses in mouse aortic tissue. The observed calcium profiles confirm results found through previous in vitro cell culture experiments. The overall procedure, including dissection, sample preparation and perfusion, takes around 3 hours to complete. Conclusion Through our unique method, we are able to induce laminar flow within intact mouse aortic tissue and illicit subsequent cellular responses. This method of ex vivo artery perfusion provides the opportunity to bridge the novel findings of in vitro studies with subsequent physiological models of fluid-shear stress mechanosensation in vascular tissues. PMID:24685068

  3. Taking the Time out of Transitions

    ERIC Educational Resources Information Center

    Guardino, Caroline; Fullerton, Elizabeth Kirby

    2014-01-01

    Until now, studies have not looked at the importance of managing and reducing academic transition times in inclusion classrooms. In the present study, researchers examine the impact of teacher-approved, environmental modifications in the context of an inclusion class. The methodology used was a single-subject, multiple baseline design across four…

  4. Oxidative stress contributes to large elastic arterial stiffening across the stages of the menopausal transition

    PubMed Central

    Hildreth, Kerry L.; Kohrt, Wendy M.; Moreau, Kerrie L.

    2015-01-01

    Objective It is unclear how changes in ovarian hormones during the menopausal transition contribute to age-associated arterial stiffening. We sought to evaluate differences in arterial stiffness and the role of oxidative stress across the stages of the menopausal transition in healthy women. Methods Arterial stiffness (carotid artery compliance and ultrasound) was measured during immediate infusions of saline (control) and ascorbic acid (experimental model to immediately decrease oxidative stress) in 97 healthy women (22-70 y) classified as premenopausal (n = 24; mean [SD] age, 33 [7] y), early perimenopausal (n = 21; 49 [3] y) or late perimenopausal (n = 21; 50 [4] y), or postmenopausal (n = 31; 57 [5] y). Results Basal carotid artery compliance was different among the groups (P < 0.001). Mean [SD] compliance was highest in premenopausal women (1.31 [0.25] mm2/mm Hg × 10−1), with progressive decrements in perimenopausal (early perimenopausal, 0.98 [0.31] mm2/mm Hg × 10−1; late perimenopausal, 0.90 [0.25] mm2/mm Hg × 10−1) and postmenopausal (0.75 [0.24] mm/mm Hg × 10−1) women. Ascorbic acid infusion improved compliance in late perimenopausal (15% [18%] increase, P = 0.001) and postmenopausal (17% [26%] increase, P = 0.002) women but not in early perimenopausal or premenopausal women. Conclusions Arterial stiffening worsens across the stages of the menopausal transition in healthy women. This seems to be mediated, in part, by oxidative stress, particularly during the late perimenopausal and postmenopausal periods. It remains uncertain whether this is specifically caused by loss of ovarian function or aging. PMID:24149926

  5. Stiffness Indices and Fractal Dimension relationship in Arterial Pressure and Diameter Time Series in-Vitro

    NASA Astrophysics Data System (ADS)

    Cymberknop, L.; Legnani, W.; Pessana, F.; Bia, D.; Zócalo, Y.; Armentano, R. L.

    2011-12-01

    The advent of vascular diseases, such as hypertension and atherosclerosis, is associated to significant alterations in the physical properties of arterial vessels. Evaluation of arterial biomechanical behaviour is related to the assessment of three representative indices: arterial compliance, arterial distensibility and arterial stiffness index. Elasticity is the most important mechanical property of the arterial wall, whose natures is strictly non-linear. Intervention of elastin and collagen fibres, passive constituent elements of the arterial wall, is related to the applied wall stress level. Concerning this, appropriate tools are required to analyse the temporal dynamics of the signals involved, in order to characterize the whole phenomenon. Fractal geometry can be mentioned as one of those techniques. The aim of this study consisted on arterial pressure and diameter signals processing, by means of nonlinear techniques based on fractal geometry. Time series morphology was related to different arterial stiffness states, generated by means of blood flow variations, during experiences performed in vitro.

  6. Linking age, survival, and transit time distributions

    NASA Astrophysics Data System (ADS)

    Calabrese, Salvatore; Porporato, Amilcare

    2015-10-01

    Although the concepts of age, survival, and transit time have been widely used in many fields, including population dynamics, chemical engineering, and hydrology, a comprehensive mathematical framework is still missing. Here we discuss several relationships among these quantities by starting from the evolution equation for the joint distribution of age and survival, from which the equations for age and survival time readily follow. It also becomes apparent how the statistical dependence between age and survival is directly related to either the age dependence of the loss function or the survival-time dependence of the input function. The solution of the joint distribution equation also allows us to obtain the relationships between the age at exit (or death) and the survival time at input (or birth), as well as to stress the symmetries of the various distributions under time reversal. The transit time is then obtained as a sum of the age and survival time, and its properties are discussed along with the general relationships between their mean values. The special case of steady state case is analyzed in detail. Some examples, inspired by hydrologic applications, are presented to illustrate the theory with the specific results. This article was corrected on 11 Nov 2015. See the end of the full text for details.

  7. TRANSITION TO COLLATERAL FLOW AFTER ARTERIAL OCCLUSION PREDISPOSES TO CEREBRAL VENOUS STEAL

    PubMed Central

    Pranevicius, Osvaldas; Pranevicius, Mindaugas; Pranevicius, Henrikas; Liebeskind, David S.

    2011-01-01

    Introduction Stroke related tissue pressure increase in the core (Pcore) and penumbra (Ppen) determines regional cerebral perfusion pressure (rCPP) defined as a difference between local inflow pressure (Pi) and venous (Pv) or tissue pressure, whichever is higher. We previously showed that venous pressure reduction below the Pcore causes blood flow diversion - cerebral venous steal. Now we investigated how transition to collateral circulation after complete arterial occlusion affects rCPP distribution. Methods We modified two parallel Starling resistor model to simulate transition to collateral inflow after complete main stem occlusion. We decreased Pv from the arterial pressure (Pa) to zero, and investigated how arterial and venous pressure elevation augments rCPP. Results When core pressure exceeded venous (Pcore>Pv), rCPP=Pi−Pcore. Venous pressure (Pv) decrease from Pa to Pcore caused smaller Pi to drop augmenting rCPP. Further drop of Pv to Ppen decreased rCPP in the core but augmented rCPP in penumbra. After transition to collateral circulation, lowering Pv below Ppen further decreased rCPP and collaterals themselves became pathway for steal. Venous pressure level at which rCPP in the core becomes zero we termed the “point of no reflow” (PONR). Transition from direct to collateral circulation resulted in decreased Pi, decreased rCPP, and a shift of PONR to higher venous loading values. Arterial pressure augmentation increased rCPP, but only after venous pressure exceeded PONR. Conclusion In the presence of tissue pressure gradients, transition to collateral flow predisposes to venous steal (collateral failure) which may be reversed by venous pressure augmentation. PMID:22246692

  8. Time Domain Estimation of Arterial Parameters using the Windkessel Model and the Monte Carlo Method

    NASA Astrophysics Data System (ADS)

    Gostuski, Vladimir; Pastore, Ignacio; Rodriguez Palacios, Gaspar; Vaca Diez, Gustavo; Moscoso-Vasquez, H. Marcela; Risk, Marcelo

    2016-04-01

    Numerous parameter estimation techniques exist for characterizing the arterial system using electrical circuit analogs. However, they are often limited by their requirements and usually high computational burdain. Therefore, a new method for estimating arterial parameters based on Monte Carlo simulation is proposed. A three element Windkessel model was used to represent the arterial system. The approach was to reduce the error between the calculated and physiological aortic pressure by randomly generating arterial parameter values, while keeping constant the arterial resistance. This last value was obtained for each subject using the arterial flow, and was a necessary consideration in order to obtain a unique set of values for the arterial compliance and peripheral resistance. The estimation technique was applied to in vivo data containing steady beats in mongrel dogs, and it reliably estimated Windkessel arterial parameters. Further, this method appears to be computationally efficient for on-line time-domain estimation of these parameters.

  9. Transit Timing Variations In Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Sansone, Eric; Haghighipour, N.

    2012-01-01

    We present the results of a study of the effect of a stellar companion on the transit timing variations (TTV) of a planetary system. The purpose of our study is to determine the ranges of the orbital elements of a secondary star for which the amplitude of a currently existing TTV is enhanced. We chose the system of Kepler 9 as this system represents the first planetary system detected by the transit timing variation method, and studied its TTVs by considering a hypothetical secondary star in this system. By varying the mass, semi-major axis, and eccentricity of the fictitious binary companion, we tested the stability of the known planets Kepler-9c and Kepler-9b and identified the region of the parameter-space for which the binary planetary system would be stable. We calculated TTVs for the two planets of the system for different values of the orbital elements of the secondary star and calculated its difference with the system's already existing TTVs. Results of our study indicate that the effect of the binary companion is significant only when the secondary star is in a highly eccentric orbit and/or the planets of the system are within the range of Super-Earth or terrestrial sizes. This work was funded by the National Science Foundation in the form of a Research Experience for Undergraduates program at the University of Hawaii at Manoa.

  10. Theory of transit time ultrasonic flowmeters

    NASA Astrophysics Data System (ADS)

    Hemp, J.

    1982-09-01

    A theory of transit time ultrasonic flowmeters for clean fluids is developed from the equations of fluid mechanics applied simultaneously to the fluid and the sound vibrations. These equations are linearized (weak sound) and use is made of the electroacoustic reciprocity theorem to give a relation between the voltages and currents at the transducer terminals and the fluid velocity. The technique of "reciprocal operation" of a transit time ultrasonic flowmeter is described and the way this technique eliminates zero drift is explained. The theory can be applied to meters with broad sound beams (which provide a better average over velocity profiles) or meters in which the wavelength of sound is not necessarily small compared with the duct diameter. Small modificaition of the sound field (due to flow) is assumed and the resulting phase (or amplitude) shift of the received signal is expressed as an integral throughout the fluid of the dot product of the fluid velocity and a weight vector defined in terms of the sound fields in the stationary fluid. Simple flowmeter designs which approach the ideal of complete immunity to velocity distribution are described.

  11. Transition to first-time motherhood.

    PubMed

    Miller, Tina

    2011-02-01

    Becoming a mother for the first time signals a major life transition for many women. But even though age at first birth now spans a broader spectrum in the UK, women's ideas of what mothering will actually entail can remain narrowly focused. Yet everyday experiences of new mothering can feel very different from the ways in which it had been anticipated, envisaged and prepared for. In this article the experiences of a small group of women will be traced as they become mothers for the first time. This qualitative, longitudinal research approach reveals a gap between the women's expectations and their unfolding mothering experiences. In turn, the unexpected hard work and exhaustion of caring for a new baby can leave women confused and ambivalent about their early mothering experiences. These findings have implications for how antenatal preparation and postnatal care are planned and delivered. PMID:21388007

  12. Hemodynamics of left internal mammary artery bypass graft: Effect of anastomotic geometry, coronary artery stenosis, and postoperative time.

    PubMed

    Fan, Tingting; Lu, Yuan; Gao, Yan; Meng, Jie; Tan, Wenchang; Huo, Yunlong; Kassab, Ghassan S

    2016-03-21

    Although the left internal mammary artery (LIMA) bypass graft is the best choice for surgical revascularization, its hemodynamics are still complex and can result in long-term graft failure. Here, we performed a hemodynamic analysis of the LIMA-coronary artery with end-to-side/side-to-side anastomoses based on 15 patient-specific CTA images at various postoperative periods. We hypothesize that hemodynamic patterns are determined by the interplay of LIMA geometry, anastomotic configuration, and severity of native coronary artery stenosis, which are strongly affected by the postoperative time. A 3D finite volume method with the inlet pressure wave and outlet resistance boundary conditions was used to compute the distribution of pressure and flow, from which the time-averaged wall shear stress (TAWSS), oscillation shear index (OSI), time-averaged WSS gradient (TAWSSG), and transverse WSS (transWSS) were determined. To characterize the hemodynamic environment, we defined surface area ratios of low TAWSS (≤4dynes/cm(2)), high OSI (≥0.15), TAWSSG (≥500dynes/cm(3)), and transWSS (≥6dynes/cm(2)) in the LIMA graft and at the anastomosis between LIMA graft and coronary artery. These ratios were determined by the interplay of multiple morphometric parameters in the LIMA-coronary artery, but increased with postoperative time. These findings have significant implications for understanding LIMA graft patency. PMID:26900034

  13. Measuring bovine mammary gland blood flow using a transit time ultrasonic flow probe.

    PubMed

    Gorewit, R C; Aromando, M C; Bristol, D G

    1989-07-01

    Lactating cattle were used to validate a transit time ultrasonic blood flow metering system for measuring mammary gland arterial blood flow. Blood flow probes were surgically placed around the right external pudic artery. An electromagnetic flow probe was implanted in tandem with the ultrasonic probe in two cows for comparative measurements. The absolute accuracy of the implanted flow probes was assessed in vivo by mechanical means on anesthetized cows after 2 to 3 wk of implantation. The zero offset of the ultrasonic probes ranged from -12 to 8 ml/min. When the ultrasonic probe was properly implanted, the slopes of the calibration curves were linear and ranged from .92 to .95, tracking absolute flow to within 8%. The transit time instrument's performance was examined under a variety of physiological conditions. These included milking and hormone injections. The transit time ultrasonic flow meter accurately measured physiological changes in mammary arterial blood flow in chronically prepared conscious cattle. Blood flow increased 29% during milking. Epinephrine decreased mammary blood flow by 90 to 95%. Oxytocin doses increased mammary blood flow by 15 to 24%. PMID:2674232

  14. Systolic aortic pressure-time area is a useful index describing arterial wave properties in rats with diabetes.

    PubMed

    Chang, Ru-Wen; Chang, Chun-Yi; Wu, Ming-Shiou; Yu, Hsi-Yu; Luo, Jian-Ming; Chen, Yih-Sharng; Lin, Fang-Yue; Lai, Liang-Chuan; Wang, Chih-Hsien; Chang, Kuo-Chu

    2015-01-01

    The accurate measurement of arterial wave properties in terms of arterial wave transit time (τw) and wave reflection factor (Rf) requires simultaneous records of aortic pressure and flow signals. However, in clinical practice, it will be helpful to describe the pulsatile ventricular afterload using less-invasive parameters if possible. We investigated the possibility of systolic aortic pressure-time area (PTAs), calculated from the measured aortic pressure alone, acting as systolic workload imposed on the rat diabetic heart. Arterial wave reflections were derived using the impulse response function of the filtered aortic input impedance spectra. The cardiovascular condition in the rats with either type 1 or type 2 diabetes was characterized by (1) an elevation in PTAs; and (2) an increase in Rf and decrease in τw. We found that an inverse linear correlation between PTAs and arterial τw reached significance (τw = 38.5462 - 0.0022 × PTAs; r = 0.7708, P < 0.0001). By contrast, as the PTAs increased, the reflection intensity increased: Rf = -0.5439 + 0.0002 × PTAs; r = 0.8701; P <0 .0001. All these findings suggested that as diabetes stiffened aortas, the augmented aortic PTAs might act as a useful index describing the diabetes-related deterioration in systolic ventricular workload. PMID:26620634

  15. A Catalog of Transit Timing Posterior Distributions for all Kepler Planet Candidate Transit Events

    NASA Astrophysics Data System (ADS)

    Montet, Benjamin Tyler; Becker, Juliette C.; Johnson, John Asher

    2015-12-01

    Kepler has ushered in a new era of planetary dynamics, enabling the detection of interactions between multiple planets in transiting systems for hundreds of systems. These interactions, observed as transit timing variations (TTVs), have been used to find non-transiting companions to transiting systems and to measure masses, eccentricities, and inclinations of transiting planets. Often, physical parameters are inferred by comparing the observed light curve to the result of a photodynamical model, a time-intensive process that often ignores the effects of correlated noise in the light curve. Catalogs of transit timing observations have previously neglected non-Gaussian uncertainties in the times of transit, uncertainties in the transit shape, and short cadence data. Here, I present a catalog of not only times of transit centers, but also posterior distributions on the time of transit for every planet candidate transit event in the Kepler data, developed through importance sampling of each transit. This catalog allows one to marginalize over uncertainties in the transit shape and incorporate short cadence data, the effects of correlated noise, and non-Gaussian posteriors. Our catalog will enable dynamical studies that reflect accurately the precision of Kepler and its limitations without requiring the computational power to model the light curve completely with every integration. I will also present our open-source N-body photodynamical modeling code, which integrates planetary and stellar orbits accounting for the effects of GR, tidal effects, and Doppler beaming.

  16. TRANSIT TIMING OBSERVATIONS FROM KEPLER. VIII. CATALOG OF TRANSIT TIMING MEASUREMENTS OF THE FIRST TWELVE QUARTERS

    SciTech Connect

    Mazeh, Tsevi; Nachmani, Gil; Holczer, Tomer; Sokol, Gil; Fabrycky, Daniel C.; Ford, Eric B.; Ragozzine, Darin; Sanchis-Ojeda, Roberto; Rowe, Jason F.; Lissauer, Jack J.; Zucker, Shay; Agol, Eric; Carter, Joshua A.; Quintana, Elisa V.; Steffen, Jason H.; Welsh, William

    2013-10-01

    Following the works of Ford et al. and Steffen et al. we derived the transit timing of 1960 Kepler objects of interest (KOIs) using the pre-search data conditioning light curves of the first twelve quarters of the Kepler data. For 721 KOIs with large enough signal-to-noise ratios, we obtained also the duration and depth of each transit. The results are presented as a catalog for the community to use. We derived a few statistics of our results that could be used to indicate significant variations. Including systems found by previous works, we have found 130 KOIs that showed highly significant times of transit variations (TTVs) and 13 that had short-period TTV modulations with small amplitudes. We consider two effects that could cause apparent periodic TTV—the finite sampling of the observations and the interference with the stellar activity, stellar spots in particular. We briefly discuss some statistical aspects of our detected TTVs. We show that the TTV period is correlated with the orbital period of the planet and with the TTV amplitude.

  17. Successful intraoperative identification of an anomalous origin of the left coronary artery from the pulmonary artery using real time three-dimensional transesophageal echocardiography.

    PubMed

    Jin, Yao Dong; Hsiung, Ming C; Tsai, Shen Kou; Chang, Chung-Yi; Wei, Jeng; Ou, Ching-huei; Chang, Yi Cheng; Lee, Kuo Chen; Sue, Sung-How

    2011-08-01

    Anomalous origin of the left coronary artery (LCA) from the pulmonary artery (ALCAPA) is a rare congenital defect that presents only infrequently in adults. An adult diagnosed with ALCAPA, heart failure, and mitral regurgitation underwent surgical ligation of the anomalous origin of the LCA from the pulmonary artery (PA) and coronary artery bypass grafting (CABG). The anomalous origin in the PA and proximal segment of the left anterior descending artery (LAD) was successfully delineated via real time, three-dimensional transesophageal echocardiography during surgery. This modality allows for fast assessment and novel views of complex cardiac abnormalities and can aid in perioperative monitoring.  PMID:21564280

  18. A virtual instrument for real time in vivo measurement of carotid artery compliance.

    PubMed

    Joseph, Jayaraj; Jayashankar, V

    2008-01-01

    A new virtual instrument for real time, non invasive measurement of carotid artery compliance is proposed. The instrument is a reliable, compact and low cost alternative to the conventional ultrasound scanner and wall tracking system for carotid artery compliance measurement. The measurement system uses an ultrasound pulse echo method to probe the carotid artery. The reflected echoes are processed using Hilbert transform techniques. Peak detection and echo tracking are implemented in LabVIEW. A comparison is done between manual and automatic method of echo identification. The instrument gives a display of the variation of carotid diameter in real time and calculates the various estimates of arterial compliance from the analyzed data. The capability of the instrument to accurately determine arterial compliance measures is demonstrated by experiments performed on human subjects. PMID:19163155

  19. Pulse transit times to the capillary bed evaluated by laser Doppler flowmetry.

    PubMed

    Bernjak, Alan; Stefanovska, Aneta

    2009-03-01

    The pulse transit time (PTT) of a wave over a specified distance along a blood vessel provides a simple non-invasive index that can be used for the evaluation of arterial distensibility. Current methods of measuring the PTT determine the propagation times of pulses only in the larger arteries. We have evaluated the pulse arrival time (PAT) to the capillary bed, through the microcirculation, and have investigated its relationship to the arterial PAT to a fingertip. To do so, we detected cardiac-induced pulse waves in skin microcirculation using laser Doppler flowmetry (LDF). Using the ECG as a reference, PATs to the microcirculation were measured on the four extremities of 108 healthy subjects. Simultaneously, PATs to the radial artery of the left index finger were obtained from blood pressure recordings using a piezoelectric sensor. Both PATs correlate in similar ways with heart rate and age. That to the microcirculation is shown to be sensitive to local changes in skin perfusion induced by cooling. We introduce a measure for the PTT through the microcirculation. We conclude that a combination of LDF and pressure measurements enables simultaneous characterization of the states of the macro and microvasculature. Information about the microcirculation, including an assessment of endothelial function, may be obtained from the responses to perturbations in skin perfusion, such as temperature stress or vasoactive substances. PMID:19202235

  20. Continuous blood pressure monitoring during exercise using pulse wave transit time measurement.

    PubMed

    Lass, J; Meigas, K; Karai, D; Kattai, R; Kaik, J; Rossmann, M

    2004-01-01

    This paper gives an overview of a research, which is focused on the development of the convenient device for continuous non-invasive monitoring of arterial blood pressure. The blood pressure estimation method is based on a presumption that there is a singular relationship between the pulse wave propagation time in arterial system and blood pressure. The parameter used in this study is pulse wave transit time (PWTT). The measurement of PWTT involves the registration of two time markers, one of which is based on ECG R peak detection and another on the detection of pulse wave in peripheral arteries. The reliability of beat to beat systolic blood pressure calculation during physical exercise was the main focus for the current paper. Sixty-one subjects (healthy and hypertensive) were studied with the bicycle exercise test. As a result of current study it is shown that with the correct personal calibration it is possible to estimate the beat to beat systolic arterial blood pressure during the exercise with comparable accuracy to conventional noninvasive methods. PMID:17272172

  1. It's Time to Transition to Production, Now What?

    NASA Technical Reports Server (NTRS)

    Jansma, P. A.; Montgomery, Marc; Werntz, David; Payne, Michael

    1999-01-01

    When it's time to transition to production, it's easy to be too focused on the application itself and to overlook some areas crucial to your success. Learn about the 10 transition tasks that will ensure a smooth transition, and will prepare your organization to operate and use your system effectively.

  2. The Timing of School Transitions and Early Adolescent Problem Behavior

    PubMed Central

    Lippold, Melissa A.; Powers, Christopher J.; Syvertsen, Amy K.; Feinberg, Mark E.; Greenberg, Mark T.

    2013-01-01

    This longitudinal study investigates whether rural adolescents who transition to a new school in sixth grade have higher levels of risky behavior than adolescents who transition in seventh grade. Our findings indicate that later school transitions had little effect on problem behavior between sixth and ninth grades. Cross-sectional analyses found a small number of temporary effects of transition timing on problem behavior: Spending an additional year in elementary school was associated with higher levels of deviant behavior in the Fall of Grade 6 and higher levels of antisocial peer associations in Grade 8. However, transition effects were not consistent across waves and latent growth curve models found no effects of transition timing on the trajectory of problem behavior. We discuss policy implications and compare our findings with other research on transition timing. PMID:24089584

  3. Transit light curves with finite integration time: Fisher information analysis

    SciTech Connect

    Price, Ellen M.; Rogers, Leslie A.

    2014-10-10

    Kepler has revolutionized the study of transiting planets with its unprecedented photometric precision on more than 150,000 target stars. Most of the transiting planet candidates detected by Kepler have been observed as long-cadence targets with 30 minute integration times, and the upcoming Transiting Exoplanet Survey Satellite will record full frame images with a similar integration time. Integrations of 30 minutes affect the transit shape, particularly for small planets and in cases of low signal to noise. Using the Fisher information matrix technique, we derive analytic approximations for the variances and covariances on the transit parameters obtained from fitting light curve photometry collected with a finite integration time. We find that binning the light curve can significantly increase the uncertainties and covariances on the inferred parameters when comparing scenarios with constant total signal to noise (constant total integration time in the absence of read noise). Uncertainties on the transit ingress/egress time increase by a factor of 34 for Earth-size planets and 3.4 for Jupiter-size planets around Sun-like stars for integration times of 30 minutes compared to instantaneously sampled light curves. Similarly, uncertainties on the mid-transit time for Earth and Jupiter-size planets increase by factors of 3.9 and 1.4. Uncertainties on the transit depth are largely unaffected by finite integration times. While correlations among the transit depth, ingress duration, and transit duration all increase in magnitude with longer integration times, the mid-transit time remains uncorrelated with the other parameters. We provide code in Python and Mathematica for predicting the variances and covariances at www.its.caltech.edu/∼eprice.

  4. Evaluation of transit-time and electromagnetic flow measurement in a chronically instrumented nonhuman primate model

    NASA Technical Reports Server (NTRS)

    Koenig, S. C.; Reister, C. A.; Schaub, J.; Swope, R. D.; Ewert, D.; Fanton, J. W.; Convertino, V. A. (Principal Investigator)

    1996-01-01

    The Physiology Research Branch at Brooks AFB conducts both human and nonhuman primate experiments to determine the effects of microgravity and hypergravity on the cardiovascular system and to identify the particular mechanisms that invoke these responses. Primary investigative efforts in our nonhuman primate model require the determination of total peripheral resistance, systemic arterial compliance, and pressure-volume loop characteristics. These calculations require beat-to-beat measurement of aortic flow. This study evaluated accuracy, linearity, biocompatability, and anatomical features of commercially available electromagnetic (EMF) and transit-time flow measurement techniques. Five rhesus monkeys were instrumented with either EMF (3 subjects) or transit-time (2 subjects) flow sensors encircling the proximal ascending aorta. Cardiac outputs computed from these transducers taken over ranges of 0.5 to 2.0 L/min were compared to values obtained using thermodilution. In vivo experiments demonstrated that the EMF probe produced an average error of 15% (r = .896) and 8.6% average linearity per reading, and the transit-time flow probe produced an average error of 6% (r = .955) and 5.3% average linearity per reading. Postoperative performance and biocompatability of the probes were maintained throughout the study. The transit-time sensors provided the advantages of greater accuracy, smaller size, and lighter weight than the EMF probes. In conclusion, the characteristic features and performance of the transit-time sensors were superior to those of the EMF sensors in this study.

  5. Real-time velocimetry for evaluation of change in thickness of arterial wall.

    PubMed

    Kanai, H; Koiwa, Y

    2000-03-01

    We previously developed a new method, namely, the phased tracking method, for accurately tracking the movement of the heart wall and arterial wall based on both the phase and magnitude of the demodulated signals to determine the instantaneous position of an object. By this method, the local change in wall thickness during one heartbeat can be determined. We have now developed a real-time system for measuring change in thickness of the myocardium and arterial wall. In this system, four high-speed digital signal processing (DSP) chips are employed for obtaining the initially developed method in real time. The tracking results for both sides of the wall are superimposed on the M (motion)-mode image in the workstation, and the thickness changes of the arterial wall are displayed in real time. Using this system, reported herein, velocity signals of the arterial wall with amplitudes less than several micrometers can be successfully detected in real time with sufficient reproducibility. The elasticity of the arterial wall is evaluated by referring to the blood pressure. In in vivo experiments, the rapid response of the change in wall thickness of the carotid artery to the dose of nitroglycerine (NTG) is evaluated for a young healthy subject and a young smoker. This new real-time system offers potential for quantitative diagnosis of early-stage atherosclerosis by the transient evaluation of the rapid response of the cardiovascular system to physiological stress. PMID:10829692

  6. A novel continuous cardiac output monitor based on pulse wave transit time.

    PubMed

    Sugo, Yoshihiro; Ukawa, Teiji; Takeda, Sunao; Ishihara, Hironori; Kazama, Tomiei; Takeda, Junzo

    2010-01-01

    Monitoring cardiac output (CO) is important for the management of patient circulation in an operation room (OR) or intensive care unit (ICU). We assumed that the change in pulse wave transit time (PWTT) obtained from an electrocardiogram (ECG) and a pulse oximeter wave is correlated with the change in stroke volume (SV), from which CO is derived. The present study reports the verification of this hypothesis using a hemodynamic analysis theory and animal study. PWTT consists of a pre-ejection period (PEP), the pulse transit time through an elasticity artery (T(1)), and the pulse transit time through peripheral resistance arteries (T(2)). We assumed a consistent negative correlation between PWTT and SV under all conditions of varying circulatory dynamics. The equation for calculating SV from PWTT was derived based on the following procedures. 1. Approximating SV using a linear equation of PWTT. 2. The slope and y-intercept of the above equation were determined under consideration of vessel compliance (SV was divided by Pulse Pressure (PP)), animal type, and the inherent relationship between PP and PWTT. Animal study was performed to verify the above-mentioned assumption. The correlation coefficient of PWTT and SV became r = -0.710 (p 〈 0.001), and a good correlation was admitted. It has been confirmed that accurate continuous CO and SV measurement is only possible by monitoring regular clinical parameters (ECG, SpO2, and NIBP). PMID:21095971

  7. Oral treprostinil for the treatment of pulmonary arterial hypertension in patients transitioned from parenteral or inhaled prostacyclins: case series and treatment protocol

    PubMed Central

    Miller, Taylor; Simon, Marc A.; Ishizawar, David C.; Mathier, Michael A.

    2016-01-01

    Abstract Oral treprostinil (TRE) is a prostacylin approved for the management of pulmonary arterial hypertension (PAH). Few data exist to guide the use of oral TRE as a replacement for parenteral or inhaled prostacyclins. Therefore, the purpose of this report was to describe our experience with oral TRE to transition patients from parenteral or inhaled TRE. We describe a case series of patients admitted for a 4-day hospital stay to transition from parenteral or inhaled TRE. Appropriate criteria for transition included stable patients with improved symptoms/functional capacity, patients who could not tolerate intravenous prostacyclin due to infection or subcutaneous prostacyclin due to pain, and patient preference for transition. The dosing protocol for transition is described. A total of 9 patients generally representative of a typical PAH demographic and background medical therapy were included. Patients were initiated at either 0.5 or 1 mg 3 times daily and discharged on a median dose of 8 mg 3 times daily. Our protocol resulted in 6 of 9 patients who successfully transitioned at a median follow-up of 47 weeks. Two patients had to return to their previous prostacyclin therapy based on the presence of clinical worsening and adverse events (n = 1) and adverse events alone (n = 1). Another patient discontinued therapy due to plans for hospice care. Oral TRE may serve an important role in prostacyclin transitions in carefully selected, stable patients who receive background oral therapy for PAH. PMID:27162621

  8. Traumatic Lateral Plantar Artery Pseudoaneurysm and the Use of Time-Resolved MR Angiography

    PubMed Central

    Chang, Anthony; Foo, Li Foong

    2010-01-01

    Vascular injury resulting in pseudoaneurysm formation in the plantar aspect of the foot is an uncommon injury after trauma. Such injuries are more often reported in the lateral plantar artery rather than the medial plantar artery, most likely because of its more superficial location. Traditional modalities in diagnosis have included ultrasound and digital subtraction angiography. We present a case of traumatic pseudoaneurysm of the lateral plantar artery following a foot laceration. Diagnosis was made by the use of high-resolution, time-resolved contrast-enhanced 3D magnetic resonance angiography, also referred to as “TRICKS” (time-resolved imaging of contrast kinetics). This technique provided high spatial resolution for the arterial anatomy as well as temporal resolution which allowed better delineation of the hemodynamic characteristics of the pseudoaneurysm. Electronic supplementary material The online version of this article (doi:10.1007/s11420-010-9170-3) contains supplementary material, which is available to authorized users. PMID:21886538

  9. Cerebral Arterial Time Constant Recorded from the MCA and PICA in Normal Subjects.

    PubMed

    Kasprowicz, Magdalena; Czosnyka, Marek; Poplawska, Karolina; Reinhard, Matthias

    2016-01-01

    Cerebral arterial time constant (τ) estimates how quickly the cerebral arterial bed distal to the point of insonation is filled with arterial blood following a cardiac contraction. It is not known how τ behaves in different vascular territories in the brain. We therefore investigated the differences in τ of two cerebral arteries: the posterior inferior cerebellar artery (PICA) and the middle cerebral artery (MCA).Transcranial Doppler cerebral blood flow velocity (CBFV) in the PICA and left MCA along with Finapres arterial blood pressure (ABP) were simultaneously recorded in 35 young healthy volunteers. τ was estimated using mathematical transformations of pulse waveforms of ABP and the CBFV of the MCA and the PICA. Since τ is independent from the vessel radius, its comparison in different cerebral arteries was feasible. Mean ABP was 76.1 ± 9.6 mmHg. The CBFV of the MCA was higher than that of the PICA (59.7 ± 7.7 vs. 41.0 ± 4.5 cm/s; p < 0.000001). τ of the PICA was shorter than that of the MCA (0.15 ± 0.03 vs. 0.18 ± 0.03 s; p < 0.000001). The MCA-supplied vascular bed has a longer distal average length, measured from the place of insonation up to the small arterioles, than the PICA-supplied vascular bed. Therefore, a longer time is needed to fill it with arterial blood volume. This study thus confirms the physiological validity of the τ concept. PMID:27165908

  10. Who will be active? Predicting exercise stage transitions after hospitalization for coronary artery disease.

    PubMed

    Reid, Robert D; Tulloch, Heather; Kocourek, Jana; Morrin, Louise I; Beaton, Louise J; Papadakis, Sophia; Blanchard, Chris M; Riley, Dana L; Pipe, Andrew L

    2007-01-01

    We describe transitions between exercise stages of change in people with coronary artery disease (CAD) over a 6-month period following a CAD-related hospitalization and evaluate constructs from Protection Motivation Theory, Theory of Planned Behavior, Social Cognitive Theory, the Ecological Model, and participation in cardiac rehabilitation as correlates of stage transition. Seven hundred eighty-two adults hospitalized with CAD were recruited and administered a baseline survey including assessments of theory-based constructs and exercise stage of change. Mailed surveys were used to gather information concerning exercise stage of change and participation in cardiac rehabilitation 6 months later. Progression from pre-action stages between baseline and 6 month follow-up was associated with greater perceived efficacy of exercise to reduce risk of future disease, fewer barriers to exercise, more access to home exercise equipment, and participation in cardiac rehabilitation. Regression from already active stages between baseline and 6 month follow-up was associated with increased perceived susceptibility to a future CAD-related event, fewer intentions to exercise, lower self-efficacy, and more barriers to exercise. PMID:17487242

  11. Real-Time Evaluation of Anterior Choroidal Artery Patency During Aneurysm Clipping

    PubMed Central

    Zhao, David Y; Nayar, Vikram V; Kalhorn, Christopher G; McGrail, Kevin M; Mandir, Allen S; Minahan, Robert E

    2016-01-01

    Inadvertent occlusion of the anterior choroidal artery during aneurysm clipping can cause a disabling stroke in minutes. We evaluate the clinical utility of direct cortical motor evoked potential (MEP) monitoring during aneurysm clipping, as a real-time assessment of arterial patency, prior to performing indocyanine green videoangiography.   Direct cortical MEPs were recorded in seven patients undergoing surgery for aneurysms that involved or abutted the anterior choroidal artery. The aneurysms clipped in those seven patients included four anterior choroidal artery aneurysms and six posterior communicating artery aneurysms. Serial MEP recordings were performed during the intradural dissection, aneurysm exposure, and clip placement. A significant change in MEPs after clip placement would prompt immediate inspection and removal or repositioning of the clip. If the clip placement appeared satisfactory and MEP recordings were stable, then an intraoperative indocyanine green videoangiogram was performed to confirm obliteration of the aneurysm and patency of the arteries.  Seven patients underwent successful clipping of anterior choroidal artery aneurysms and posterior communicating artery aneurysms using direct cortical MEP monitoring, with good clinical and radiographic outcomes. In six patients, no changes in MEP amplitudes were observed following permanent clip placement. In one patient, a profound decrease in MEP amplitude occurred 220 seconds after placement of a permanent clip on a large posterior communicating aneurysm. An inspection revealed that the anterior choroidal artery was kinked. The clip was immediately removed, and the MEP signals returned to baseline shortly thereafter. A clip was then optimally placed, and the patient awoke without neurologic deficit.  Direct cortical MEPs are a useful adjunct to standard electrophysiologic monitoring in aneurysm surgery, particularly when the anterior choroidal artery or lenticulostriate arteries are at

  12. Single molecule fluorescence experiments determine protein folding transition path times

    PubMed Central

    Chung, Hoi Sung; McHale, Kevin; Louis, John M.; Eaton, William A.

    2013-01-01

    The transition path is the tiny fraction of an equilibrium molecular trajectory when a transition occurs by crossing the free-energy barrier between two states. It is a single-molecule property that contains all the mechanistic information on how a process occurs. As a step toward observing transition paths in protein folding we determined the average transition-path time for a fast- and a slow-folding protein from a photon-by-photon analysis of fluorescence trajectories in single-molecule Förster-resonance-energy-transfer experiments. While the folding rate coefficients differ by a factor of 10,000, the transition-path times differ by less than a factor of 5, showing that a fast-and a slow-folding protein take almost the same time to fold when folding actually happens. A very simple model based on energy landscape theory can explain this result. PMID:22363011

  13. Correcting transit time distributions in coarse MODFLOW-MODPATH models.

    PubMed

    Abrams, Daniel

    2013-01-01

    In low to medium resolution MODFLOW models, the area occupied by sink cells often far exceeds the surface area of the streams they represent. As a result, MODPATH will calculate inaccurate particle traces and transit times. A frequency distribution of transit times for a watershed will also be in error. Such a distribution is used to assess the long-term impact of nonpoint source pollution on surface waters and wells. Although the inaccuracies for individual particles can only be avoided by increased model grid resolution or other advanced modeling techniques, the frequency distribution can be improved by scaling the particle transit times by an adjustment factor during post-processing. PMID:22974377

  14. Smoothing the Transition to Daylight Saving Time

    MedlinePlus

    ... he said, offering the following suggestions: Adults should wake up 15 minutes earlier than usual on each of ... them for a bedtime that might otherwise feel too early. If young children go to bed late because of the time change, let them get ...

  15. AMON: Transition to real-time operations

    NASA Astrophysics Data System (ADS)

    Cowen, D. F.; Keivani, A.; Tešić, G.

    2016-04-01

    The Astrophysical Multimessenger Observatory Network (AMON) will link the world's leading high-energy neutrino, cosmic-ray, gamma-ray and gravitational wave observatories by performing real-time coincidence searches for multimessenger sources from observatories' subthreshold data streams. The resulting coincidences will be distributed to interested parties in the form of electronic alerts for real-time follow-up observation. We will present the science case, design elements, current and projected partner observatories, status of the AMON project, and an initial AMON-enabled analysis. The prototype of the AMON server has been online since August 2014 and processing archival data. Currently, we are deploying new high-uptime servers and will be ready to start issuing alerts as early as winter 2015/16.

  16. Space-time formulation of quantum transitions

    NASA Astrophysics Data System (ADS)

    Petrosky, T.; Ordonez, G.; Prigogine, I.

    2001-12-01

    In a previous paper we have studied dressed excited states in the Friedrichs model, which describes a two-level atom interacting with radiation. In our approach, excited states are distributions (or generalized functions) in the Liouville space. These states decay in a strictly exponential way. In contrast, the states one may construct in the Hilbert space of wave functions always present deviations from exponential decay. We have considered the momentum representation, which is applicable to global quantities (trace, energy transfer). Here we study the space-time description of local quantities associated with dressed unstable states, such as, the intensity of the photon field. In this situation the excited states become factorized in Gamow states. To go from local quantities to global quantities, we have to proceed to an integration over space, which is far from trivial. There are various elements that appear in the space-time evolution of the system: the unstable cloud that surrounds the bare atom, the emitted real photons and the ``Zeno photons,'' which are associated with deviations from exponential decay. We consider a Hilbert space approximation to our dressed excited state. This approximation leads already to decay close to exponential in the field surrounding the atom, and to a line shape different from the Lorentzian line shape. Our results are compared with numerical simulations. We show that the time evolution of an unstable state satisfies a Boltzmann-like H theorem. This is applied to emission and absorption as well as scattering. The existence of a microscopic H theorem is not astonishing. The excited states are ``nonequilibrium'' states and their time evolution leads to the emission of photons, which distributes the energy of the unstable state among the field modes.

  17. TRANSIT TIMING OBSERVATIONS FROM KEPLER. V. TRANSIT TIMING VARIATION CANDIDATES IN THE FIRST SIXTEEN MONTHS FROM POLYNOMIAL MODELS

    SciTech Connect

    Ford, Eric B.; Ragozzine, Darin; Holman, Matthew J.; Rowe, Jason F.; Barclay, Thomas; Borucki, William J.; Bryson, Stephen T.; Caldwell, Douglas A.; Kinemuchi, Karen; Koch, David G.; Lissauer, Jack J.; Still, Martin; Tenenbaum, Peter; Steffen, Jason H.; Batalha, Natalie M.; Fabrycky, Daniel C.; and others

    2012-09-10

    Transit timing variations provide a powerful tool for confirming and characterizing transiting planets, as well as detecting non-transiting planets. We report the results of an updated transit timing variation (TTV) analysis for 1481 planet candidates based on transit times measured during the first sixteen months of Kepler observations. We present 39 strong TTV candidates based on long-term trends (2.8% of suitable data sets). We present another 136 weaker TTV candidates (9.8% of suitable data sets) based on the excess scatter of TTV measurements about a linear ephemeris. We anticipate that several of these planet candidates could be confirmed and perhaps characterized with more detailed TTV analyses using publicly available Kepler observations. For many others, Kepler has observed a long-term TTV trend, but an extended Kepler mission will be required to characterize the system via TTVs. We find that the occurrence rate of planet candidates that show TTVs is significantly increased ({approx}68%) for planet candidates transiting stars with multiple transiting planet candidates when compared to planet candidates transiting stars with a single transiting planet candidate.

  18. Cerebral arterial bolus arrival time is prolonged in multiple sclerosis and associated with disability

    PubMed Central

    Paling, David; Thade Petersen, Esben; Tozer, Daniel J; Altmann, Daniel R; Wheeler-Kingshott, Claudia AM; Kapoor, Raju; Miller, David H; Golay, Xavier

    2014-01-01

    Alterations in the overall cerebral hemodynamics have been reported in multiple sclerosis (MS); however, their cause and significance is unknown. While potential venous causes have been examined, arterial causes have not. In this study, a multiple delay time arterial spin labeling magnetic resonance imaging sequence at 3T was used to quantify the arterial hemodynamic parameter bolus arrival time (BAT) and cerebral blood flow (CBF) in normal-appearing white matter (NAWM) and deep gray matter in 33 controls and 35 patients with relapsing–remitting MS. Bolus arrival time was prolonged in MS in NAWM (1.0±0.2 versus 0.9±0.2 seconds, P=0.031) and deep gray matter (0.90±0.18 versus 0.80±0.14 seconds, P=0.001) and CBF was increased in NAWM (14±4 versus 10±2 mL/100 g/min, P=0.001). Prolonged BAT in NAWM (P=0.042) and deep gray matter (P=0.01) were associated with higher expanded disability status score. This study demonstrates alteration in cerebral arterial hemodynamics in MS. One possible cause may be widespread inflammation. Bolus arrival time was longer in patients with greater disability independent of atrophy and T2 lesion load, suggesting alterations in cerebral arterial hemodynamics may be a marker of clinically relevant pathology. PMID:24045400

  19. Developments in Planet Detection using Transit Timing Variations

    SciTech Connect

    Steffen, Jason H.; Agol, Eric; /Washington U., Seattle, Astron. Dept.

    2006-12-01

    In a transiting planetary system, the presence of a second planet will cause the time interval between transits to vary. These transit timing variations (TTV) are particularly large near mean-motion resonances and can be used to infer the orbital elements of planets with masses that are too small to detect by any other means. The author presents the results of a study of simulated data where they show the potential that this planet detection technique has to detect and characterize secondary planets in transiting systems. These results have important ramifications for planetary transit searches since each transiting system presents an opportunity for additional discoveries through a TTV analysis. They present such an analysis for 13 transits of the HD 209458 system that were observed with the Hubble Space Telescope. This analysis indicates that a putative companion in a low-order, mean-motion resonance can be no larger than the mass of the Earth and constitutes, to date, the most sensitive probe for extrasolar planets that orbit main sequence stars. The presence or absence of small planets in low-order, mean-motion resonances has implications for theories of the formation and evolution of planetary systems. Since TTV is most sensitive in these regimes, it should prove a valuable tool not only for the detection of additional planets in transiting systems, but also as a way to determine the dominant mechanisms of planet formation and the evolution of planetary systems.

  20. Does reducing ischemia time justify to catheterize firstly the culprit artery in every primary PCI?

    PubMed

    Jurado-Román, Alfonso; García-Tejada, Julio; Hernández-Hernández, Felipe; Granda-Nistal, Carolina; Rubio-Alonso, Belén; Agudo-Quílez, Pilar; Velázquez-Martín, Maite; Albarrán-González-Trevilla, Agustín; Tascón-Pérez, Juan

    2016-07-01

    No consensus exists about which coronary artery should be firstly catheterized in primary PCIs. Initial catheterization of the "culprit artery" could reduce reperfusion time. However, complete knowledge of coronary anatomy could modify revascularization strategy. The objective of the study was to analyze this issue in ST-elevation myocardial infarction patients undergoing primary PCI. PCIs were performed in 384 consecutive patients. Choice of ipsilateral approach (IA): starting with a guiding catheter for the angiography and PCI of the "culprit artery", or contralateral approach (CA): starting with a diagnostic catheter for the "non-culprit artery" and completing the angiography and PCI of the culprit with a guiding catheter was left to the operator. Differences between two approaches regarding reperfusion time, acute events or revascularization strategies were analyzed. There were no differences between two approaches regarding reperfusion time or clinical events. When the left coronary artery was responsible, IA was more frequent (76.4 vs 22.6 %), but when it was the right coronary artery, CA was preferred (20 vs 80 %); p < 0.0001. With CA, bare metal stents (BMS) were more used than drug eluting (DES) (60.8 vs 39.2 %) inversely than with IA (BMS 41.3 vs DES 59.7 %; p < 0.0001). With CA there were more patients with left main or multivessel disease in which revascularization was completed with non-urgent surgery (4.13 vs 2.4 %, p < 0.0001). Initial CA does not involve higher reperfusion time. Furthermore, overall knowledge of coronary anatomy offers more options in revascularization strategy and may imply a change in management. Despite the need to individualize each case, contralateral approach may be the first option with the exception of unstable patients. PMID:26113458

  1. Real-time measurements of local myocardium motion and arterial wall thickening.

    PubMed

    Kanai, H; Koiwa, Y; Zhang, J

    1999-01-01

    We have already developed a new method, namely, the phased tracking method, to track the movement of the heart wall and arterial wall accurately based on both the phase and magnitude of the demodulated signals to determine the instantaneous position of an object. This method has been realized by an off-line measurement system, which cannot be applied to transient evaluation of rapid response of the cardiovascular system to physiological stress. In this paper, therefore, a real-time system to measure change in the thickness of the myocardium and the arterial wall is presented. In this system, an analytic signal from standard ultrasonic diagnostic equipment is analogue-to-digital (A/D) converted at a sampling frequency of 1 MHz. By pipelining and parallel processing using four high-speed digital signal processing (DSP) chips, the method described is realized in real time. The tracking results for both sides of the heart and/or arterial wall are superimposed on the M (motion)-mode image in the work station (WS), and the thickness changes of the heart and/or arterial wall are also displayed and digital-to-analogue (D/A) converted in real time. From the regional change in thickness of the heart wall, spatial distribution of myocardial motility and contractility can be evaluated. For the arterial wall, its local elasticity can be evaluated by referring to the blood pressure. In in vivo experiments, the rapid response of the change in wall thickness of the carotid artery to the dose of the nitroglycerine (NTG) is evaluated. This new real-time system offers potential for quantitative diagnosis of myocardial motility, early stage atherosclerosis, and the transient evaluation of the rapid response of the cardiovascular system to physiological stress. PMID:18244316

  2. The cross-sectional association of sitting time with carotid artery stiffness in young adults

    PubMed Central

    Huynh, Quan L; Blizzard, Christopher L; Sharman, James E; Magnussen, Costan G; Dwyer, Terence; Venn, Alison J

    2014-01-01

    Objectives Physical activity is negatively associated with arterial stiffness. However, the relationship between sedentary behaviour and arterial stiffness is poorly understood. In this study, we aimed to investigate the association of sedentary behaviour with arterial stiffness among young adults. Design Cross-sectional. Setting 34 study clinics across Australia during 2004–2006. Participants 2328 participants (49.4% male) aged 26–36 years who were followed up from a nationally representative sample of Australian schoolchildren in 1985. Measurements Arterial stiffness was measured by carotid ultrasound. Sitting time per weekday and weekend day, and physical activity were self-reported by questionnaire. Cardiorespiratory fitness was estimated as physical work capacity at a heart rate of 170 bpm. Anthropometry, blood pressure, resting heart rate and blood biochemistry were measured. Potential confounders, including strength training, education, smoking, diet, alcohol consumption and parity, were self-reported. Rank correlation was used for analysis. Results Sitting time per weekend day, but not per weekday, was correlated with arterial stiffness (males r=0.11 p<0.01, females r=0.08, p<0.05) and cardiorespiratory fitness (males r = −0.14, females r = −0.08, p<0.05), and also with fatness and resting heart rate. One additional hour of sitting per weekend day was associated with 5.6% (males p=0.046) and 8.6% (females p=0.05) higher risk of having metabolic syndrome. These associations were independent of physical activity and other potential confounders. The association of sitting time per weekend day with arterial stiffness was not mediated by resting heart rate, fatness or metabolic syndrome. Conclusions Our study demonstrates a positive association of sitting time with arterial stiffness. The greater role of sitting time per weekend day in prediction of arterial stiffness and cardiometabolic risk than that of sitting time per weekday may be due

  3. Oral transit time: a critical review of the literature

    PubMed Central

    SOARES, Thais Jacóe; MORAES, Danielle Pedroni; de MEDEIROS, Gisele Chagas; SASSI, Fernanda Chiarion; ZILBERSTEIN, Bruno; de ANDRADE, Claudia Regina Furquim

    2015-01-01

    Introduction Oral transit time is one of the parameters observed during the clinical assessment of the swallowing function. The importance of this parameter is due to its impact on the total duration of a meal, whose consequence can be an unfavorable nutritional prognostic. Objective To document scientific papers that measure oral transit time in healthy subjects. Method The review followed the steps proposed by the Cochrane Handbook. The search was done via the PubMed database through the use of descriptors related to the oral phase of swallowing, as well as to types of food consistency. Results The articles on the theme had different definitions for oral transit time, as well as heterogeneity of tested volumes, age and gender of the participants. The times found varied from 0.35 s to 1.54 s for liquids, from 0.39 s to 1.05 s for pasty foods and from 1 s to 12.8 s for solid foods. Also, regardless of volume or consistency, oral transit time in elderly people is significantly longer than in adults. Conclusion There's no consensus in the literature about oral transit time in healthy subjects. However, this parameter should be valued during the assessment of the swallowing function due to its negative impact on the dynamics of swallowing, which can cause high energy expenditure during feeding. PMID:26176255

  4. Domain wall formation in late-time phase transitions

    NASA Technical Reports Server (NTRS)

    Kolb, Edward W.; Wang, Yun

    1992-01-01

    We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.

  5. Nonadiabatic transitions in finite-time adiabatic rapid passage

    NASA Astrophysics Data System (ADS)

    Lu, T.; Miao, X.; Metcalf, H.

    2007-06-01

    To apply the adiabatic rapid passage process repetitively [T. Lu, X. Miao, and H. Metcalf, Phys. Rev. A 71, 061405(R) (2005)], the nonadiabatic transition probability of a two-level atom subject to chirped light pulses over a finite period of time needs to be calculated. Using a unitary first-order perturbation method in the rotating adiabatic frame, an approximate formula has been derived for such transition probabilities in the entire parameter space of the pulses.

  6. TTVFaster: First order eccentricity transit timing variations (TTVs)

    NASA Astrophysics Data System (ADS)

    Agol, Eric; Deck, Katherine

    2016-04-01

    TTVFaster implements analytic formulae for transit time variations (TTVs) that are accurate to first order in the planet–star mass ratios and in the orbital eccentricities; the implementations are available in several languages, including IDL, Julia, Python and C. These formulae compare well with more computationally expensive N-body integrations in the low-eccentricity, low mass-ratio regime when applied to simulated and to actual multi-transiting Kepler planet systems.

  7. STELLAR PROPER MOTION AND THE TIMING OF PLANETARY TRANSITS

    SciTech Connect

    Rafikov, Roman R.

    2009-08-01

    Duration and period of transits in extrasolar planetary systems can exhibit long-term variations for a variety of reasons. Here we investigate how systemic proper motion, which steadily re-orients planetary orbit with respect to our line of sight, affects the timing of transits. We find that in a typical system with a period of several days, proper motion at the level of 100 mas yr{sup -1} makes transit duration vary at a rate {approx}10-100 ms yr{sup -1}. In some isolated systems this variation is at the measurable level (can be as high as 0.6 s yr{sup -1} for GJ436) and may exceed all other transit-timing contributions (due to the general relativity, stellar quadrupole, etc.). In addition, proper motion causes evolution of the observed period between transits P {sub obs} via the Shklovskii effect at a rate {approx}>10 {mu}s yr{sup -1} for the nearby transiting systems (0.26 ms yr{sup -1} in GJ436), which in some cases exceeds all other contributions to P-dot{sub obs}. Earth's motion around the Sun gives rise to additional periodic timing signal (even for systems with zero intrinsic proper motion) allowing a full determination of the spatial orientation of the planetary orbit. Unlike most other timing effects, the proper motion signatures persist even in systems with zero eccentricity and get stronger as the planetary period increases. They should be the dominant cause of transit-timing variations in isolated wide-separation (periods of months) systems that will be sought by Kepler.

  8. How do starspots influence the transit timing variations of exoplanets? Simulations of individual and consecutive transits

    NASA Astrophysics Data System (ADS)

    Ioannidis, P.; Huber, K. F.; Schmitt, J. H. M. M.

    2016-01-01

    Transit timing variations (TTVs) of exoplanets are normally interpreted as the consequence of gravitational interaction with additional bodies in the system. However, TTVs can also be caused by deformations of the system transits by starspots, which might thus pose a serious complication in their interpretation. We therefore simulate transit light curves deformed by spot-crossing events for different properties of the stellar surface and the planet, such as starspot position, limb darkening, planetary period, and impact parameter. Mid-transit times determined from these simulations can be significantly shifted with respect to the input values; these shifts cannot be larger than 1% of the transit duration and depend very strongly on the longitudinal position of the spot during the transit and the transit duration. Consequently, TTVs with amplitudes larger than the above limit are very unlikely to be caused by starspots. We also investigate whether TTVs from sequences of consecutive transits with spot-crossing anomalies can be misinterpreted as the result of an additional body in the system. We use the Generalized Lomb-Scargle periodogram to search for periods in TTVs and conclude that low-amplitude TTVs with statistically significant periods around active stars are the most problematic cases. In those cases where the photometric precision is high enough to inspect the transit shapes for deformations it should be possible to identify TTVs caused by starspots; however, especially for cases with low signal-to-noise in transit (TSNR ≲ 15) light curves it becomes quite difficult to reliably decide whether these periods come from starspots, physical companions in the system, or if they are random noise artifacts.

  9. Transit time and charge storage measurements in heavily doped emitters

    NASA Technical Reports Server (NTRS)

    Neugroschel, A.; Park, J. S.; Hwang, B. Y.

    1986-01-01

    A first direct measurement of the minority-carrier transit time in a transparent heavily doped emitter layer is reported. The value was obtained by a high-frequency conductance method recently developed and used for low-doped Si. The transit time coupled with the steady-state current enables the determination of the quasi-static charge stored in the emitter and the quasi-static emitter capacitance. Using a transport model, from the measured transit time, the value for the minority-carrier diffusion coefficient and mobility is estimated. The measurements were done using a heavily doped emitter of the Si p(+)-n-p bipolar transistor. The new result indicates that the position-averaged minority-carrier diffusion coefficients may be much smaller than the corresponding majority-carrier values for emitters having a concentration ranging from about 3 x 10 to the 19th per cu cm to 10 to the 20th per cu cm.

  10. Reliable estimation of capillary transit time distributions using DSC-MRI

    PubMed Central

    Mouridsen, Kim; Hansen, Mikkel Bo; Østergaard, Leif; Jespersen, Sune Nørhøj

    2014-01-01

    The regional availability of oxygen in brain tissue is traditionally inferred from the magnitude of cerebral blood flow (CBF) and the concentration of oxygen in arterial blood. Measurements of CBF are therefore widely used in the localization of neuronal response to stimulation and in the evaluation of patients suspected of acute ischemic stroke or flow-limiting carotid stenosis. It was recently demonstrated that capillary transit time heterogeneity (CTH) limits maximum oxygen extraction fraction (OEFmax) that can be achieved for a given CBF. Here we present a statistical approach for determining CTH, mean transit time (MTT), and CBF using dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI). Using numerical simulations, we demonstrate that CTH, MTT, and OEFmax can be estimated with low bias and variance across a wide range of microvascular flow patterns, even at modest signal-to-noise ratios. Mean transit time estimated by singular value decomposition (SVD) deconvolution, however, is confounded by CTH. The proposed technique readily identifies malperfused tissue in acute stroke patients and appears to highlight information not detected by the standard SVD technique. We speculate that this technique permits the non-invasive detection of tissue with impaired oxygen delivery in neurologic disorders such as acute ischemic stroke and Alzheimer's disease during routine diagnostic imaging. PMID:24938401

  11. Educating Part-Time Adult Learners in Transition. ERIC Digest.

    ERIC Educational Resources Information Center

    Conrad, Judi

    Adult learners, who comprise over half of all students in higher education, are typically part-time students in transition and present special challenges to colleges and universities. These students are primarily seeking to improve their situation through education, and their commitment to self-improvement dictates a different set of aspirations…

  12. Caregivers' Playfulness and Infants' Emotional Stress during Transitional Time

    ERIC Educational Resources Information Center

    Jung, Jeesun

    2011-01-01

    The purpose of this study is to explore the playfulness of the teachers of infants and its relations to infants' emotional distress during the transitional time at a child care centre. The study used a qualitative case study. Two infant caregivers in a university-based child care centre participated in this study. For the three-month research…

  13. Analysis of flow disturbance in a stenosed carotid artery bifurcation using two-equation transitional and turbulence models.

    PubMed

    Tan, F P P; Soloperto, G; Bashford, S; Wood, N B; Thom, S; Hughes, A; Xu, X Y

    2008-12-01

    In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter's hybrid k-epsilon/k-omega shear stress transport (SST) model and its "scale adaptive simulation" (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant. PMID:19045537

  14. Radial electron-beam-breakup transit-time oscillator

    SciTech Connect

    Mostrom, M.A.; Kwan, T.J.T.

    1995-01-01

    A new radially-driven electron-beam-breakup transit-time oscillator has been investigated analytically and through computer simulation as a compact low-impedance high-power microwave generator. In a 1MV, 50kA device 35cm in radius and 15cm long, with no external magnetic field, 5GW of extracted power and a growth rate of 0.26/ns have been observed. Theoretical maximum efficiencies are several times higher.

  15. Transit timing at Toruń Center for Astronomy

    NASA Astrophysics Data System (ADS)

    Bykowski, W.; Maciejewski, G.

    2011-01-01

    The transit monitoring is one of well-known methods for discovering and observing new extrasolar planets. Among various advantages, this way of searching other worlds does not require complex and expensive equipment -- it can be performed with a relatively small telescope and high-quality CCD camera. At the Center for Astronomy of Nicolaus Copernicus University in Toruń, Poland, we collect observational data using the 60-cm Cassegrain telescope hoping that it would be possible to discover new objects in already known planetary systems using the transit timing variation method. Our observations are a part of a bigger cooperation between observatories from many countries.

  16. Spectral diagnosis of human coronary artery: a clinical system for real-time analysis

    NASA Astrophysics Data System (ADS)

    Kramer, John R., Jr.; Brennan, James F., III; Roemer, Tjeerd J.; Wang, Yang; Dasari, Ramachandra R.; Feld, Michael S.

    1995-05-01

    In vitro studies have shown that normal and abnormal human coronary artery segments can be differentiated on the basis of their Raman spectra. A compact near infrared Raman spectroscopy system has been constructed for in vivo measurement of the biochemical composition of human coronary artery. A 500 mW air-cooled diode laser generates 830 nm excitation light which is delivered via a fiber optic probe to the arterial wall. Scattered light is collected by the same optical probe and delivered to a f/1.8 imaging spectrograph, which disperses the light onto a liquid-nitrogen-cooled deep-depletion CCD detector. A spectral model has been developed to quantify the protein, lipid and calcium mineral content in coronary artery wall. Raman spectra with sufficiently high S/N for extracting biochemical information can be collected in less than one second. In vivo studies during open heart surgery are currently being conducted which will establish near infrared Raman techniques as a real- time diagnostic tool.

  17. Time delay between cardiac and brain activity during sleep transitions

    NASA Astrophysics Data System (ADS)

    Long, Xi; Arends, Johan B.; Aarts, Ronald M.; Haakma, Reinder; Fonseca, Pedro; Rolink, Jérôme

    2015-04-01

    Human sleep consists of wake, rapid-eye-movement (REM) sleep, and non-REM (NREM) sleep that includes light and deep sleep stages. This work investigated the time delay between changes of cardiac and brain activity for sleep transitions. Here, the brain activity was quantified by electroencephalographic (EEG) mean frequency and the cardiac parameters included heart rate, standard deviation of heartbeat intervals, and their low- and high-frequency spectral powers. Using a cross-correlation analysis, we found that the cardiac variations during wake-sleep and NREM sleep transitions preceded the EEG changes by 1-3 min but this was not the case for REM sleep transitions. These important findings can be further used to predict the onset and ending of some sleep stages in an early manner.

  18. Psychiatric and Familial Predictors of Transition Times Between Smoking Stages

    PubMed Central

    Sartor, Carolyn E.; Xian, Hong; Scherrer, Jeffrey F.; Lynskey, Michael T.; Duncan, Alexis E.; Haber, J. Randolph; Grant, Julia D.; Bucholz, Kathleen K.; Jacob, Theodore

    2008-01-01

    The modifying effects of psychiatric and familial risk factors on age at smoking initiation, rate of progression from first cigarette to regular smoking, and transition time from regular smoking to nicotine dependence (ND) were examined in 1,269 offspring of male twins from the Vietnam Era Twin Registry. Mean age of the sample was 20.1 years. Cox proportional hazard regression analyses adjusting for paternal alcohol dependence and ND status and maternal ND were conducted. Both early age at first cigarette and rapid transition from initiation to regular smoking were associated with externalizing disorders, alcohol consumption, and cannabis use. Rapid escalation from regular smoking to ND was also predicted by externalizing disorders, but in contrast to earlier transitions, revealed a strong association with internalizing disorders and no significant relationship with use of other substances. Findings characterize a rarely examined aspect of the course of ND development and highlight critical distinctions in risk profiles across stages of tobacco involvement. PMID:17900819

  19. Visual Analysis and Comparison of Kepler Transit Timing Variations

    NASA Astrophysics Data System (ADS)

    Kane, Mackenzie; Ragozzine, Darin; Holczer, Tomer; Mazeh, Tsevi; Rowe, Jason

    2016-01-01

    NASA's Kepler Space Telescope is designed to find extrasolar planets by watching a section of the sky and observing if an object transits in front its parent star. By noticing the dimming and brightening of the star as a prospective transit occurs, Kepler records the times when the planet moves in front of its star. If other planets are gravitationally influencing the transiting planet, the planet might transit late or early; these deviations from a perfectly periodic set of transits are called "transit timing variations (TTVs). Therefore, Kepler TTVs are useful in determining exoplanet masses which are hard to measure in other ways.We decided to visually analyze the TTV data of all ~6000 Kepler objects of interest (KOIs) to determine whether interesting TTV signals would be missed by purely statistical analyses. Using data from Rowe et al. 2014 and Holczer et al. 2015, submitted, we created combined TTV plots, periodigrams, and folded quadratic+sinusoid fits. The raw TTV data and ancillary plots were visually inspected for each of the ~6000 KOIs. To find the most likely KOIs containing visible TTVs and to organize the over 6000 KOIs analyzed, a rating system was developed based on numerous visual factors. These rating factors include the amount of outliers, if there is a clear sinusoidal period within the folded plots, and if there is a clear peak in the periodigram. By sorting KOIs as such, we were able to compare our findings of the strongest candidates with the same KOIs statistically analyzed by Holczer et al. 2015 (submitted, see also Mazeh et al. 2013).It was found that the majority of our findings matched those of Holczer et al. 2015, with only small discrepancies that were understandable based on our different methodologies. Our visual inspection of the full list of KOIs contributed multiple systems that were not included in the initial list of KOIs with significant TTVs identified statistically.

  20. Real-Time Automatic Artery Segmentation, Reconstruction and Registration for Ultrasound-Guided Regional Anaesthesia of the Femoral Nerve.

    PubMed

    Smistad, Erik; Lindseth, Frank

    2016-03-01

    The goal is to create an assistant for ultrasound- guided femoral nerve block. By segmenting and visualizing the important structures such as the femoral artery, we hope to improve the success of these procedures. This article is the first step towards this goal and presents novel real-time methods for identifying and reconstructing the femoral artery, and registering a model of the surrounding anatomy to the ultrasound images. The femoral artery is modelled as an ellipse. The artery is first detected by a novel algorithm which initializes the artery tracking. This algorithm is completely automatic and requires no user interaction. Artery tracking is achieved with a Kalman filter. The 3D artery is reconstructed in real-time with a novel algorithm and a tracked ultrasound probe. A mesh model of the surrounding anatomy was created from a CT dataset. Registration of this model is achieved by landmark registration using the centerpoints from the artery tracking and the femoral artery centerline of the model. The artery detection method was able to automatically detect the femoral artery and initialize the tracking in all 48 ultrasound sequences. The tracking algorithm achieved an average dice similarity coefficient of 0.91, absolute distance of 0.33 mm, and Hausdorff distance 1.05 mm. The mean registration error was 2.7 mm, while the average maximum error was 12.4 mm. The average runtime was measured to be 38, 8, 46 and 0.2 milliseconds for the artery detection, tracking, reconstruction and registration methods respectively. PMID:26513782

  1. Electron transit time measurements of 5-in photomultiplier tubes

    NASA Astrophysics Data System (ADS)

    Richards, T.; Peatross, J.; Ware, M.; Rees, L.

    2016-08-01

    We investigated the uniformity of electron transit times for two 5-in photomultiplier tubes: the Hamamatsu R1250 and the Adit B133D01S. We focused a highly attenuated short-pulse laser on the tubes while they were mounted on a programmable stage. The stage translated the tubes relative to the incident beam so that measurements could be made with light focused at points along a grid covering the entire photocathodes. A portion of the incident light was split from the incident beam and measured and recorded by a fast photodiode. Electron transit times were measured by computing the time delay between the recorded photodiode signal and photomultiplier signal using software constant-fraction discrimination. The Hamamatsu tube exhibited a uniform timing response that varied by no more than 1.7 ns. The Adit tube was much less uniform, with transit times that varied by as much as 57 ns. The Adit response also exhibited a spatially varying double-peak structure in its response. The technique described in this paper could be usefully employed by photomultiplier tube manufacturers to characterize the performance of their products.

  2. Biomechanics of Ergometric Stress Test: regional and local effects on elastic, transitional and muscular human arteries

    NASA Astrophysics Data System (ADS)

    Valls, G.; Torrado, J.; Farro, I.; Bia, D.; Zócalo, Y.; Lluberas, S.; Craiem, D.; Armentano, Rl

    2011-09-01

    Ergometric exercise stress tests (EST) give important information about the cardiovascular (CV) response to increased demands. The expected EST-related changes in variables like blood pressure and heart rate are known, but those in the arterial biomechanics are controversial and incompletely characterized. In this context, this work aims were to characterize the regional and local arterial biomechanical behaviour in response to EST; to evaluate its temporal profile in the post-EST recovery phase; and to compare the biomechanical response of different to EST. Methods: In 16 non-trained healthy young subjects the carotid-femoral pulse wave velocity and the carotid, femoral and brachial arterial distensibility were non-invasively evaluated before (Rest) and after EST. Main results: The EST resulted in an early increase in the arterial stiffness, evidenced by both, regional and local parameters (pulse wave velocity increase and distensibility reduction). When analyzing conjunctly the different post-EST recovery stages there were quali-quantitative differences among the arterial local stiffness response to EST. The biomechanical changes could not be explained only by blood pressure variations.

  3. Time-resolved PIV measurements of the flow field in a stenosed, compliant arterial model

    NASA Astrophysics Data System (ADS)

    Geoghegan, P. H.; Buchmann, N. A.; Soria, J.; Jermy, M. C.

    2013-05-01

    Compliant (flexible) structures play an important role in several biological flows including the lungs, heart and arteries. Coronary heart disease is caused by a constriction in the artery due to a build-up of atherosclerotic plaque. This plaque is also of major concern in the carotid artery which supplies blood to the brain. Blood flow within these arteries is strongly influenced by the movement of the wall. To study these problems experimentally in vitro, especially using flow visualisation techniques, can be expensive due to the high-intensity and high-repetition rate light sources required. In this work, time-resolved particle image velocimetry using a relatively low-cost light-emitting diode illumination system was applied to the study of a compliant flow phantom representing a stenosed (constricted) carotid artery experiencing a physiologically realistic flow wave. Dynamic similarity between in vivo and in vitro conditions was ensured in phantom construction by matching the distensibility and the elastic wave propagation wavelength and in the fluid system through matching Reynolds ( Re) and Womersley number ( α) with a maximum, minimum and mean Re of 939, 379 and 632, respectively, and a α of 4.54. The stenosis had a symmetric constriction of 50 % by diameter (75 % by area). Once the flow rate reached a critical value, Kelvin-Helmholtz instabilities were observed to occur in the shear layer between the main jet exiting the stenosis and a reverse flow region that occurred at a radial distance of 0.34 D from the axis of symmetry in the region on interest 0-2.5 D longitudinally downstream from the stenosis exit. The instability had an axis-symmetric nature, but as peak flow rate was approached this symmetry breaks down producing instability in the flow field. The characteristics of the vortex train were sensitive not only to the instantaneous flow rate, but also to whether the flow was accelerating or decelerating globally.

  4. Characteristics of time-varying intracranial pressure on blood flow through cerebral artery: A fluid-structure interaction approach.

    PubMed

    Syed, Hasson; Unnikrishnan, Vinu U; Olcmen, Semih

    2016-02-01

    Elevated intracranial pressure is a major contributor to morbidity and mortality in severe head injuries. Wall shear stresses in the artery can be affected by increased intracranial pressures and may lead to the formation of cerebral aneurysms. Earlier research on cerebral arteries and aneurysms involves using constant mean intracranial pressure values. Recent advancements in intracranial pressure monitoring techniques have led to measurement of the intracranial pressure waveform. By incorporating a time-varying intracranial pressure waveform in place of constant intracranial pressures in the analysis of cerebral arteries helps in understanding their effects on arterial deformation and wall shear stress. To date, such a robust computational study on the effect of increasing intracranial pressures on the cerebral arterial wall has not been attempted to the best of our knowledge. In this work, fully coupled fluid-structure interaction simulations are carried out to investigate the effect of the variation in intracranial pressure waveforms on the cerebral arterial wall. Three different time-varying intracranial pressure waveforms and three constant intracranial pressure profiles acting on the cerebral arterial wall are analyzed and compared with specified inlet velocity and outlet pressure conditions. It has been found that the arterial wall experiences deformation depending on the time-varying intracranial pressure waveforms, while the wall shear stress changes at peak systole for all the intracranial pressure profiles. PMID:26701867

  5. Studying time-like baryonic transitions with HADES

    NASA Astrophysics Data System (ADS)

    Ramstein, B.

    2016-05-01

    Recent results of the HADES collaboration are presented with emphasis on the e+e- production in elementary reactions. Via the Dalitz decay of baryonic resonances (R →Ne+e-), access is given to the time-like electromagnetic structure of baryonic transitions. This process could be measured for the first time for Δ(1232) in pp reactions at 1.25 GeV. At higher energies, the sensitivity of e+e- emission to transition form factors of the Vector Dominance type has been demonstrated. Very recently, experiments with the GSI pion beam started, allowing for more direct studies of baryonic resonances Dalitz decays. In addition, the measurement of hadronic channels provides a new data base for baryon spectroscopy issues, in particular in the 2πN channel.

  6. The time of a photoinduced spin-Peierls phase transition

    SciTech Connect

    Semenov, A. L.

    2015-02-15

    The time τ of the spin-Peierls phase transition is analyzed theoretically as a function of the duration τ{sub p} of the exciting light pulse and the average number x{sub 0} of absorbed photons per magnetic ion after the transmission of the pulse. It is shown that the phase transition occurs at x{sub 0} > x{sub c}. The critical value x{sub c} is determined as a function of the duration τ{sub p} of the light pulse. A photoinduced variation in the optical reflection coefficient R is calculated as a function of time t. The results of calculation are compared with experimental data on ultrafast photoinduced melting of the low-temperature spin-Peierls phase into potassium tetracyanoquinodimethan (K-TCNQ)

  7. Coupling of transit time instabilities in electrostatic confinement fusion devices

    SciTech Connect

    Gruenwald, J. Fröhlich, M.

    2015-07-15

    A model of the behavior of transit time instabilities in an electrostatic confinement fusion reactor is presented in this letter. It is demonstrated that different modes are excited within the spherical cathode of a Farnsworth fusor. Each of these modes is dependent on the fusion products as well as the acceleration voltage applied between the two electrodes and they couple to a resulting oscillation showing non-linear beat phenomena. This type of instability is similar to the transit time instability of electrons between two resonant surfaces but the presence of ions and the occurring fusion reactions alter the physics of this instability considerably. The physics of this plasma instability is examined in detail for typical physical parameter ranges of electrostatic confinement fusion devices.

  8. New contributions to transit-time damping in multidimensional systems

    NASA Technical Reports Server (NTRS)

    Robinson, P. A.

    1989-01-01

    The existence of two previously unrecognized contributions to transit-time damping in systems of more than one dimension is demonstrated and discussed. It is shown that these contributions cannot be treated by one-dimensional analyses unless it is assumed that the gradient of the field perpendicular to itself always vanishes. Such an assumption is unjustified in general and the new contributions can dominate damping by fast particles in more general situations. Analytic expressions obtained using a Born approximation are found to be in excellent agreement with numerical test-particle calculations of transit-time damping for a variety of field configurations. These configurations include those of a resonance layer and of a spherical wave packet, which approximates a collapsing wave packet in a strongly turbulent plasma. It is found that the fractional power absorption can be strongly enhanced in non-slablike field configurations.

  9. Coupling of transit time instabilities in electrostatic confinement fusion devices

    NASA Astrophysics Data System (ADS)

    Gruenwald, J.; Fröhlich, M.

    2015-07-01

    A model of the behavior of transit time instabilities in an electrostatic confinement fusion reactor is presented in this letter. It is demonstrated that different modes are excited within the spherical cathode of a Farnsworth fusor. Each of these modes is dependent on the fusion products as well as the acceleration voltage applied between the two electrodes and they couple to a resulting oscillation showing non-linear beat phenomena. This type of instability is similar to the transit time instability of electrons between two resonant surfaces but the presence of ions and the occurring fusion reactions alter the physics of this instability considerably. The physics of this plasma instability is examined in detail for typical physical parameter ranges of electrostatic confinement fusion devices.

  10. Transit time instabilities in an inverted fireball. I. Basic properties

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Gruenwald, J.; Fonda, B.; Ionita, C.; Schrittwieser, R.

    2011-01-01

    A new fireball configuration has been developed which produces vircator-like instabilities. Electrons are injected through a transparent anode into a spherical plasma volume. Strong high-frequency oscillations with period corresponding to the electron transit time through the sphere are observed. The frequency is below the electron plasma frequency, hence does not involve plasma eigenmodes. The sphere does not support electromagnetic eigenmodes at the instability frequency. However, the rf oscillations on the gridded anode create electron bunches which reinforce the grid oscillation after one transit time or rf period, which leads to an absolute instability. Various properties of the instability are demonstrated and differences to the sheath-plasma instability are pointed out, one of which is a relatively high conversion efficiency from dc to rf power. Nonlinear effects are described in a companion paper [R. L. Stenzel et al., Phys. Plasmas 18, 012105 (2011)].

  11. Vessel-selective, non-contrast enhanced, time-resolved MR angiography with vessel-selective arterial spin labeling technique (CINEMA-SELECT) in intracranial arteries.

    PubMed

    Nakamura, Masanobu; Yoneyama, Masami; Tabuchi, Takashi; Takemura, Atsushi; Obara, Makoto; Tatsuno, Satoshi; Sawano, Seishi

    2013-07-01

    We demonstrate the feasibility of the vessel-selective, non-contrast, time-resolved magnetic resonance angiography (MRA) technique, "contrast inherent inflow enhanced multi-phase angiography combining vessel-selective arterial spin labeling technique (CINEMA-SELECT)". This sequence consists of two major techniques: pulsed star labeling of arterial regions (PULSAR) and Look-Locker sampling. We hypothesize that this technique allows selective labeling of single intracranial arteries, consisting of high-resolution four-dimensional data with a wide coverage of the brain. In this study, a new vessel-selective, time-resolved angiographic technique is demonstrated that can produce individual angiograms non-invasively by labeling the principal arterial vessels proximal to the circle of Willis. Clear vessel delineation is achieved, and the separation of the three vessels is evident in healthy volunteers. This technique could play an important role in the assessment of the structure and hemodynamics of intracranial arteries without the use of contrast agents. PMID:23475783

  12. Transit-time spin field-effect transistor

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian; Monsma, Douwe J.

    2007-06-01

    The authors propose and analyze a four-terminal metal-semiconductor device that uses hot-electron transport through thin ferromagnetic films to inject and detect a charge-coupled spin current transported through the conduction band of an arbitrary semiconductor. This provides the possibility of realizing a spin field-effect transistor in Si using electrostatic transit-time control of coherent spin precession in a perpendicular magnetic field.

  13. Tunnel transit-time (TUNNETT) devices for terahertz sources

    NASA Technical Reports Server (NTRS)

    Haddad, G. I.; East, J. R.; Kidner, C.

    1991-01-01

    The potential and capabilities of tunnel transit-time (TUNNETT) devices for power generation in the 100-1000 GHz range are presented. The basic properties of these devices and the important material parameters which determine their properties are discussed and criteria for designing such devices are presented. It is shown from a first-order model that significant amounts of power can be obtained from these devices in the terahertz frequency range.

  14. Smartphone-based Continuous Blood Pressure Measurement Using Pulse Transit Time.

    PubMed

    Gholamhosseini, Hamid; Meintjes, Andries; Baig, Mirza; Linden, Maria

    2016-01-01

    The increasing availability of low cost and easy to use personalized medical monitoring devices has opened the door for new and innovative methods of health monitoring to emerge. Cuff-less and continuous methods of measuring blood pressure are particularly attractive as blood pressure is one of the most important measurements of long term cardiovascular health. Current methods of noninvasive blood pressure measurement are based on inflation and deflation of a cuff with some effects on arteries where blood pressure is being measured. This inflation can also cause patient discomfort and alter the measurement results. In this work, a mobile application was developed to collate the PhotoPlethysmoGramm (PPG) waveform provided by a pulse oximeter and the electrocardiogram (ECG) for calculating the pulse transit time. This information is then indirectly related to the user's systolic blood pressure. The developed application successfully connects to the PPG and ECG monitoring devices using Bluetooth wireless connection and stores the data onto an online server. The pulse transit time is estimated in real time and the user's systolic blood pressure can be estimated after the system has been calibrated. The synchronization between the two devices was found to pose a challenge to this method of continuous blood pressure monitoring. However, the implemented continuous blood pressure monitoring system effectively serves as a proof of concept. This combined with the massive benefits that an accurate and robust continuous blood pressure monitoring system would provide indicates that it is certainly worthwhile to further develop this system. PMID:27225558

  15. Improved diagnosis and management of hyper- and hypothyroidism by timing the arterial sounds.

    PubMed

    Young, R T; Van Herle, A J; Rodbard, D

    1976-02-01

    "Sphygmo-Recording," a non-invasive method for timing the arterial pulse wave contour provides an objective measure of responses to medication in patients with hyper- and hypothyroidism. The QKd interval, i.e., the interval from the onset of the QRS complex (Q) to the onset of the Korotkoff sounds (K) at the brachial artery when the sphygmomanometer cuff is at diastolic pressure (d) is the QKd interval. QKd is normally 205 +/- 12 msec. In the hyperthyroidism the QKd interval may be shortened to 110 msec. In hypothyroidism the QKd interval may be prolonged to 320 msec. Changes in QKd parallel changes in clinical status and serum total T4 and T3, measured by radioimmunoassay. QKd can be used as an objective guide to antithyroid therapy in hyperthyroidism and replacement therapy with thyroid hormone in hypothyroid individuals. PMID:1262433

  16. Comparison of noninvasive pulse transit time estimates as markers of blood pressure using invasive pulse transit time measurements as a reference.

    PubMed

    Gao, Mingwu; Olivier, N Bari; Mukkamala, Ramakrishna

    2016-05-01

    Pulse transit time (PTT) measured as the time delay between invasive proximal and distal blood pressure (BP) or flow waveforms (invasive PTT [I-PTT]) tightly correlates with BP PTT estimated as the time delay between noninvasive proximal and distal arterial waveforms could therefore permit cuff-less BP monitoring. A popular noninvasive PTT estimate for this application is the time delay between ECG and photoplethysmography (PPG) waveforms (pulse arrival time [PAT]). Another estimate is the time delay between proximal and distal PPG waveforms (PPG-PTT). PAT and PPG-PTT were assessed as markers of BP over a wide physiologic range using I-PTT as a reference. Waveforms for determining I-PTT, PAT, and PPG-PTT through central arteries were measured from swine during baseline conditions and infusions of various hemodynamic drugs. Diastolic, mean, and systolic BP varied widely in each subject (group average (mean ± SE) standard deviation between 25 ± 2 and 36 ± 2 mmHg). I-PTT correlated well with all BP levels (group average R(2) values between 0.86 ± 0.03 and 0.91 ± 0.03). PPG-PTT also correlated well with all BP levels (group average R(2) values between 0.81 ± 0.03 and 0.85 ± 0.02), and its R(2) values were not significantly different from those of I-PTT PAT correlated best with systolic BP (group average R(2) value of 0.70 ± 0.04), but its R(2) values for all BP levels were significantly lower than those of I-PTT (P < 0.005) and PPG-PTT (P < 0.02). The pre-ejection period component of PAT was responsible for its inferior correlation with BP In sum, PPG-PTT was not different from I-PTT and superior to the popular PAT as a marker of BP. PMID:27233300

  17. Lifetime measurements in transitional nuclei by fast electronic scintillation timing

    NASA Astrophysics Data System (ADS)

    Caprio, M. A.; Zamfir, N. V.; Casten, R. F.; Amro, H.; Barton, C. J.; Beausang, C. W.; Cooper, J. R.; Gürdal, G.; Hecht, A. A.; Hutter, C.; Krücken, R.; McCutchan, E. A.; Meyer, D. A.; Novak, J. R.; Pietralla, N.; Ressler, J. J.; Berant, Z.; Brenner, D. S.; Gill, R. L.; Regan, P. H.

    2002-10-01

    A new generation of experiments studying nuclei in spherical-deformed transition regions has been motivated by the introduction of innovative theoretical approaches to the treatment of these nuclei. The important structural signatures in the transition regions, beyond the basic yrast level properties, involve γ-ray transitions between low-spin, non-yrast levels, and so information on γ-ray branching ratios and absolute matrix elements (or level lifetimes) for these transitions is crucial. A fast electronic scintillation timing (FEST) system [H. Mach, R. L. Gill, and M. Moszyński, Nucl. Instrum. Methods A 280, 49 (1989)], making use of BaF2 and plastic scintillation detectors, has been implemented at the Yale Moving Tape Collector for the measurement of lifetimes of states populated in β^ decay. Experiments in the A100 (Pd, Ru) and A150 (Dy, Yb) regions have been carried out, and a few examples will be presented. Supported by the US DOE under grants and contracts DE-FG02-91ER-40609, DE-FG02-88ER-40417, and DE-AC02-98CH10886 and by the German DFG under grant Pi 393/1.

  18. Implantable reflectance pulse transit time blood pressure sensor with oximetry capability

    NASA Astrophysics Data System (ADS)

    Fiala, J.; Gehrke, R.; Theodor, M.; Bingger, P.; Förster, K.; Heilmann, C.; Beyersdorf, F.; Zappe, H.; Seifert, A.

    2010-04-01

    We present a novel implantable multi-wavelength reflectance sensor for the measurement of blood pressure with pulse transit time (PTT). Continuous long-term monitoring of blood pressure and arterial oxygen saturation is vital for medical diagnostics and the ensuing therapy of cardiovascular diseases. Conventional cuff-based blood pressure monitors do not provide continuous data and put severe constraints on the patients' daily lives. An implantable sensor would eliminate such problems. The new biocompatible sensor is placed subcutaneously on blood perfused tissue. The PTT is calculated by photoplethysmograms and the ECG-signal, that is recorded with intracorporal electrodes. In addition, the sensor detects the arterial oxygen saturation. An ensuing spectralphotometric analysis of the light intensity changes delivers data on the concentration of dysfunctional hemoglobin derivatives. Experimental measurements showed a clear correlation between the estimated PTT and the systolic blood pressure reference. These initial results demonstrate the potential of the sensor as part of an fully implantable sensor system for the longterm-monitoring of cardiovascular parameters.

  19. Transit time spreads in biased paracentric hemispherical deflection analyzers

    NASA Astrophysics Data System (ADS)

    Sise, Omer; Zouros, Theo J. M.

    2016-02-01

    The biased paracentric hemispherical deflection analyzers (HDAs) are an alternative to conventional (centric) HDAs maintaining greater dispersion, lower angular aberrations, and hence better energy resolution without the use of any additional fringing field correctors. In the present work, the transit time spread of the biased paracentric HDA is computed over a wide range of analyzer parameters. The combination of high energy resolution with good time resolution and simplicity of design makes the biased paracentric analyzers very promising for both coincidence and singles spectroscopy applications.

  20. Experimental occlusion of the central artery of the retina. IV: Retinal tolerance time to acute ischaemia.

    PubMed Central

    Hayreh, S. S.; Weingeist, T. A.

    1980-01-01

    Ophthalmoscopic, fluorescein angiographic, electrophysiological, and morphological studies on 63 eyes of rhesus monkeys with acute transient experimental occlusion of the central artery of the retina (OCAR) showed that the retina suffered irreparable damage after ischaemia of 105 minutes but recovered well after ischaemia of 97-98 minutes. The tolerance time of the brain to acute transient ischaemia is many times shorter than that of the retina. The metabolism of ischaemic neurones (in the retina and brain) is discussed with a view to explaining this difference, and also the various factors possibly responsible for the retina's longer tolerance to ischaemia, as compared to the brain. PMID:7426553

  1. H ∞ synchronization of the coronary artery system with input time-varying delay

    NASA Astrophysics Data System (ADS)

    Xiao-Meng, Li; Zhan-Shan, Zhao; Jing, Zhang; Lian-Kun, Sun

    2016-06-01

    This paper investigates the H ∞ synchronization of the coronary artery system with input delay and disturbance. We focus on reducing the conservatism of existing synchronization strategies. Base on the triple integral forms of the Lyapunov–Krasovskii functional (LKF), we utilize single and double integral forms of Wirtinger-based inequality to guarantee that the synchronization feedback controller has good performance against time-varying delay and external disturbance. The effectiveness of our strategy can be exhibited by simulations under the different time-varying delays and different disturbances. Project supported by the National Natural Science Foundation of China (Grant Nos. 61503280, 61403278, and 61272006).

  2. Real-time Assessment of Flow Reversal in an Eccentric Arterial Stenotic Model

    PubMed Central

    Ai, Lisong; Zhang, Lequan; Dai, Wangde; Hu, Changhong; Shung, K. Kirk; Hsiai, Tzung K.

    2010-01-01

    Plaque rupture is the leading cause of acute coronary syndromes and stroke. Plaque formation, or otherwise known as stenosis, preferentially occurs in the regions of arterial bifurcation or curvatures. To date, real-time assessment of stenosis-induced flow reversal remains a clinical challenge. By interfacing Micro-electro-mechanical Systems (MEMS) thermal sensors with the high frequency Pulsed Wave (PW) Doppler ultrasound, we proposed to assess flow reversal in the presence of an eccentric stenosis. We developed a 3-D stenotic model (inner diameter of 6 mm, an eccentric stenosis with a height of 2.75mm and width of 21 mm) simulating a superficial arterial vessel. We demonstrated that heat transfer from the sensing element (2 × 80 μm) to the flow field peaked as a function of flow rates at the throat of the stenosis alone the center/midline of arterial model, and dropped downstream from the stenosis where flow reversal was detected by the high frequency ultrasound device at 45 MHz. Computational fluid dynamics (CFD) codes were in agreement with the ultrasound-acquired flow profiles upstream, downstream, and at the throat of the stenosis. Hence, we characterized regions of eccentric stenosis in terms of changes in heat transfer alone the midline of vessel and identified points of flow reversal with high spatial and temporal resolution. PMID:20655537

  3. Optimizing the search for transiting planets in long time series

    NASA Astrophysics Data System (ADS)

    Ofir, Aviv

    2014-01-01

    Context. Transit surveys, both ground- and space-based, have already accumulated a large number of light curves that span several years. Aims: The search for transiting planets in these long time series is computationally intensive. We wish to optimize the search for both detection and computational efficiencies. Methods: We assume that the searched systems can be described well by Keplerian orbits. We then propagate the effects of different system parameters to the detection parameters. Results: We show that the frequency information content of the light curve is primarily determined by the duty cycle of the transit signal, and thus the optimal frequency sampling is found to be cubic and not linear. Further optimization is achieved by considering duty-cycle dependent binning of the phased light curve. By using the (standard) BLS, one is either fairly insensitive to long-period planets or less sensitive to short-period planets and computationally slower by a significant factor of ~330 (for a 3 yr long dataset). We also show how the physical system parameters, such as the host star's size and mass, directly affect transit detection. This understanding can then be used to optimize the search for every star individually. Conclusions: By considering Keplerian dynamics explicitly rather than implicitly one can optimally search the BLS parameter space. The presented Optimal BLS enhances the detectability of both very short and very long period planets, while allowing such searches to be done with much reduced resources and time. The Matlab/Octave source code for Optimal BLS is made available. The MATLAB code is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A138

  4. [Comparative study of 2 methods of measuring intestinal transit time].

    PubMed

    Vidal-Neira, L; León-Barúa, R

    1981-01-01

    In 20 healthy volunteers, intestinal transit times, obtained following a simple method, recently described, in which a small liquid-containing rubber bag is used as a marker, were compared with the times obtained following, simultaneously, another method, already universally accepted, in which small barium-impregnated pellets are used as markers. The intestinal transit determined with the rubber bag (TTI-B) (14.1 - 79.2 hours; mean +/- s.d.: 42.4 +/- 20.7 hours) were significantly shorter than the times determined with the plastic pellets (TTI) (26.4 - 88.1 hours; mean +/- s.d.: 60.2 +/- 25.5 hours (P less than 0.001). But, TTI-B and TTI correlate closely (r: + 0.86), and, furthermore, TTI-B results may be converted to TTI results with the help of a simple regression equation: TTI (in minutes) = 831 + 1.09 TTI-B (in minutes). After analyzing what has been observed in the present work and in previous works, it was concluded that the new method to measure intestinal transient time using the small rubber bag is reliable and simple, and that it may help to better understand what happens in some important gastrointestinal problems. PMID:7342626

  5. Using long time series of agricultural-derived nitrates for estimating catchment transit times

    NASA Astrophysics Data System (ADS)

    Fovet, O.; Ruiz, L.; Faucheux, M.; Molénat, J.; Sekhar, M.; Vertès, F.; Aquilina, L.; Gascuel-Odoux, C.; Durand, P.

    2015-03-01

    The estimation of water and solute transit times in catchments is crucial for predicting the response of hydrosystems to external forcings (climatic or anthropogenic). The hydrogeochemical signatures of tracers (either natural or anthropogenic) in streams have been widely used to estimate transit times in catchments as they integrate the various processes at stake. However, most of these tracers are well suited for catchments with mean transit times lower than about 4-5 years. Since the second half of the 20th century, the intensification of agriculture led to a general increase of the nitrogen load in rivers. As nitrate is mainly transported by groundwater in agricultural catchments, this signal can be used to estimate transit times greater than several years, even if nitrate is not a conservative tracer. Conceptual hydrological models can be used to estimate catchment transit times provided their consistency is demonstrated, based on their ability to simulate the stream chemical signatures at various time scales and catchment internal processes such as N storage in groundwater. The objective of this study was to assess if a conceptual lumped model was able to simulate the observed patterns of nitrogen concentration, at various time scales, from seasonal to pluriannual and thus if it was relevant to estimate the nitrogen transit times in headwater catchments. A conceptual lumped model, representing shallow groundwater flow as two parallel linear stores with double porosity, and riparian processes by a constant nitrogen removal function, was applied on two paired agricultural catchments which belong to the Research Observatory ORE AgrHys. The Global Likelihood Uncertainty Estimation (GLUE) approach was used to estimate parameter values and uncertainties. The model performance was assessed on (i) its ability to simulate the contrasted patterns of stream flow and stream nitrate concentrations at seasonal and inter-annual time scales, (ii) its ability to simulate the

  6. Predictable Patterns in Planetary Transit Timing Variations and Transit Duration Variations Due to Exomoons

    NASA Technical Reports Server (NTRS)

    Heller, Rene; Hippke, Michael; Placek, Ben; Angerhausen, Daniel; Agol, Eric

    2016-01-01

    We present new ways to identify single and multiple moons around extrasolar planets using planetary transit timing variations (TTVs) and transit duration variations (TDVs). For planets with one moon, measurements from successive transits exhibit a hitherto undescribed pattern in the TTV-TDV diagram, originating from the stroboscopic sampling of the planet's orbit around the planet-moon barycenter. This pattern is fully determined and analytically predictable after three consecutive transits. The more measurements become available, the more the TTV-TDV diagram approaches an ellipse. For planets with multiple moons in orbital mean motion resonance (MMR), like the Galilean moon system, the pattern is much more complex and addressed numerically in this report. Exomoons in MMR can also form closed, predictable TTV-TDV figures, as long as the drift of the moons' pericenters is suciently slow.We find that MMR exomoons produce loops in the TTV-TDV diagram and that the number of these loops is equal to the order of the MMR, or the largest integer in the MMR ratio.We use a Bayesian model and Monte Carlo simulations to test the discoverability of exomoons using TTV-TDV diagrams with current and near-future technology. In a blind test, two of us (BP, DA) successfully retrieved a large moon from simulated TTV-TDV by co-authors MH and RH, which resembled data from a known Kepler planet candidate. Single exomoons with a 10 percent moon-to-planet mass ratio, like to Pluto-Charon binary, can be detectable in the archival data of the Kepler primary mission. Multi-exomoon systems, however, require either larger telescopes or brighter target stars. Complementary detection methods invoking a moon's own photometric transit or its orbital sampling effect can be used for validation or falsification. A combination of TESS, CHEOPS, and PLATO data would offer a compelling opportunity for an exomoon discovery around a bright star.

  7. Predictable patterns in planetary transit timing variations and transit duration variations due to exomoons

    NASA Astrophysics Data System (ADS)

    Heller, René; Hippke, Michael; Placek, Ben; Angerhausen, Daniel; Agol, Eric

    2016-06-01

    We present new ways to identify single and multiple moons around extrasolar planets using planetary transit timing variations (TTVs) and transit duration variations (TDVs). For planets with one moon, measurements from successive transits exhibit a hitherto undescribed pattern in the TTV-TDV diagram, originating from the stroboscopic sampling of the planet's orbit around the planet-moon barycenter. This pattern is fully determined and analytically predictable after three consecutive transits. The more measurements become available, the more the TTV-TDV diagram approaches an ellipse. For planets with multiple moons in orbital mean motion resonance (MMR), like the Galilean moon system, the pattern is much more complex and addressed numerically in this report. Exomoons in MMR can also form closed, predictable TTV-TDV figures, as long as the drift of the moons' pericenters is sufficiently slow. We find that MMR exomoons produce loops in the TTV-TDV diagram and that the number of these loops is equal to the order of the MMR, or the largest integer in the MMR ratio. We use a Bayesian model and Monte Carlo simulations to test the discoverability of exomoons using TTV-TDV diagrams with current and near-future technology. In a blind test, two of us (BP, DA) successfully retrieved a large moon from simulated TTV-TDV by co-authors MH and RH, which resembled data from a known Kepler planet candidate. Single exomoons with a 10% moon-to-planet mass ratio, like to Pluto-Charon binary, can be detectable in the archival data of the Kepler primary mission. Multi-exomoon systems, however, require either larger telescopes or brighter target stars. Complementary detection methods invoking a moon's own photometric transit or its orbital sampling effect can be used for validation or falsification. A combination of TESS, CHEOPS, and PLATO data would offer a compelling opportunity for an exomoon discovery around a bright star.

  8. Factors associated with extubation time in coronary artery bypass grafting patients

    PubMed Central

    Rezaianzadeh, Abbas; Maghsoudi, Behzad; Tabatabaee, Hamidreza; Keshavarzi, Sareh; Bagheri, Zahra; Sajedianfard, Javad; Gerami, Hamid

    2015-01-01

    Background and Objectives. Cardiovascular diseases are the leading cause of death worldwide, with coronary artery disease being the most common. With increasing numbers of patients, Coronary Artery Bypass Grafting (CABG) has become the most common operation in the world. Respiratory disorder is one of the most prevalent complications of CABG. Thus, weaning off the mechanical ventilation and extubation are of great clinical importance for these patients. Some post-operative problems also relate to the tracheal tube and mechanical ventilation. Therefore, an increase in this leads to an increase in the number of complications, length of hospital stay, and treatment costs. Since a large number of factors affect the post-operative period, the present study aims to identify the predictors of extubation time in CABG patients using casualty network analysis. Method. This longitudinal study was conducted on 800 over 18 year old patients who had undergone CABG surgery in three treatment centers affiliated to Shiraz University of Medical Sciences. The patients’ information, including pre-operative, peri-operative, and post-operative variables, was retrospectively extracted from their medical records. Then, the data was comprehensively analyzed through path analysis using MPLUS-7.1 software. Results. The mean of extubation time was 10.27 + 4.39 h. Moreover, extubation time was significantly affected by packed cells during the Cardiopulmonary Bypass (CPB), packed cells after CPB, inotrope use on arrival at ICU, mean arterial pressure 1st ICU, packed cells 1st ICU, platelets 1st ICU, Blood Urea Nitrogen 1st ICU, and hematocrit 1st ICU. Conclusion. Considering all of the factors under investigation, some peri-operative and post-operative factors had significant effects. Therefore, considering the post-operative factors is important for designing a treatment plan and evaluating patients’ prognosis. PMID:26644972

  9. Analysis of transit time spread on FBK silicon photomultipliers

    NASA Astrophysics Data System (ADS)

    Acerbi, F.; Gola, A.; Ferri, A.; Zorzi, N.; Paternoster, G.; Piemonte, C.

    2015-07-01

    In this paper we studied one of the aspects potentially limiting the single-photon time-resolution (SPTR) of the silicon photomultiplier (SiPM): the transit time spread (TTS). We illuminated the SiPM in different positions with a fast-pulsed laser collimated to a circular spot of 0.2 mm-diameter and acquired bi-dimensional maps of the avalanche-signal arrival time of RGB and RGB-HD SiPMs, produced at FBK. We studied the effect of both the number of bonding wires connecting the device to the package and the layout of the top-metal connection (on the device). We found that the TTS does not simply depend on the trace length between the cell and the bonding pad and it could vary in the range between tens of picoseconds (with 3 bonding connections) to more than one hundred of picoseconds (with one connection).

  10. Radial electron-beam-breakup transit-time oscillator

    DOEpatents

    Kwan, Thomas J. T.; Mostrom, Michael A.

    1998-01-01

    A radial electron-beam-breakup transit-time oscillator (RBTO) provides a compact high power microwave generator. The RBTO includes a coaxial vacuum transmission line having an outer conductor and an inner conductor. The inner conductor defines an annular cavity with dimensions effective to support an electromagnetic field in a TEM.sub.00m mode. A radial field emission cathode is formed on the outer conductor for providing an electron beam directed toward the annular cavity electrode. Microwave energy is then extracted from the annular cavity electrode.

  11. Time-resolved fluorescence spectra of arterial fluorescent compounds: reconstruction with the Laguerre expansion technique.

    PubMed

    Maarek, J M; Marcu, L; Snyder, W J; Grundfest, W S

    2000-02-01

    The time-resolved fluorescence spectra of the main arterial fluorescent compounds were retrieved using a new algorithm based on the Laguerre expansion of kernels technique. Samples of elastin, collagen and cholesterol were excited with a pulsed nitrogen laser and the emission was measured at 29 discrete wavelengths between 370 and 510 nm. The expansion of the fluorescence impulse response function on the Laguerre basis of functions was optimized to reproduce the observed fluorescence emission. Collagen lifetime (5.3 ns at 390 nm) was substantially larger than that of elastin (2.3 ns) and cholesterol (1.3 ns). Two decay components were identified in the emission decay of the compounds. For collagen, the decay components were markedly wavelength dependent and hydration dependent such that the emission decay became shorter at higher emission wavelengths and with hydration. The decay characteristics of elastin and cholesterol were relatively unchanged with wavelength and with hydration. The observed variations in the time-resolved spectra of elastin, collagen and cholesterol were consistent with the existence of several fluorophores with different emission characteristics. Because the compounds are present in different proportions in healthy and atherosclerotic arterial walls, characteristic differences in their time-resolved emission spectra could be exploited to assess optically the severity of atherosclerotic lesions. PMID:10687392

  12. Analytical approximation of transit time scattering due to magnetosonic waves

    NASA Astrophysics Data System (ADS)

    Bortnik, J.; Thorne, R. M.; Ni, B.; Li, J.

    2015-03-01

    Recent test particle simulations have shown that energetic electrons traveling through fast magnetosonic (MS) wave packets can experience an effect which is specifically associated with the tight equatorial confinement of these waves, known as transit time scattering. However, such test particle simulations can be computationally cumbersome and offer limited insight into the dominant physical processes controlling the wave-particle interactions, that is, in determining the effects of the various wave parameters and equatorial confinement on the particle scattering. In this paper, we show that such nonresonant effects can be effectively captured with a straightforward analytical treatment that is made possible with a set of reasonable, simplifying assumptions. It is shown that the effect of the wave confinement, which is not captured by the standard quasi-linear theory approach, acts in such a way as to broaden the range of particle energies and pitch angles that can effectively resonate with the wave. The resulting diffusion coefficients can be readily incorporated into global diffusion models in order to test the effects of transit time scattering on the dynamical evolution of radiation belt fluxes.

  13. The length and time scales of water's glass transitions

    NASA Astrophysics Data System (ADS)

    Limmer, David T.

    2014-06-01

    Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids.

  14. Space and time renormalization in phase transition dynamics

    DOE PAGESBeta

    Francuz, Anna; Dziarmaga, Jacek; Gardas, Bartłomiej; Zurek, Wojciech H.

    2016-02-18

    Here, when a system is driven across a quantum critical point at a constant rate, its evolution must become nonadiabatic as the relaxation time τ diverges at the critical point. According to the Kibble-Zurek mechanism (KZM), the emerging post-transition excited state is characterized by a finite correlation length ξˆ set at the time tˆ=τˆ when the critical slowing down makes it impossible for the system to relax to the equilibrium defined by changing parameters. This observation naturally suggests a dynamical scaling similar to renormalization familiar from the equilibrium critical phenomena. We provide evidence for such KZM-inspired spatiotemporal scaling by investigatingmore » an exact solution of the transverse field quantum Ising chain in the thermodynamic limit.« less

  15. Racial Differences in the Association between Carotid Plaque and Aortic and Coronary Artery Calcification Among Women Transitioning the Menopause

    PubMed Central

    Woodard, Genevieve A.; Narla, Vinod V.; Ye, Rong; Cauley, Jane A.; Thompson, Trina; Matthews, Karen A.; Sutton-Tyrrell, Kim

    2011-01-01

    Background Carotid atherosclerosis is a marker for atherosclerotic disease in other vascular beds; however, racial differences in this association have not been fully examined. The purpose of this report is to evaluate racial differences in the relationship between carotid plaque and calcification in the aorta and coronary arteries among women transitioning the menopause. Methods 540 African American and White women with a median age of 50 years were evaluated from the Study of Women’s Health Across the Nation. Carotid plaque (none versus any) was assessed with B-mode ultrasound and aortic (AC; 0, >0–100, >100) and coronary artery calcification (CAC; 0, >0–10, >10) with computed tomography. Results For the total cohort, higher prevalence of plaque was significantly associated with higher levels of AC, but not CAC. The interaction of race and carotid plaque was significant in models with AC and CAC as dependent variables (p=0.03, 0.002, respectively). Among African Americans, there was an inverse relationship, although not significant, between carotid plaque and high AC (>100) (OR 0.75, 95%CI: 0.10–5.48), and between plaque and high CAC (>10) (OR 0.20, 95%CI: 0.03–1.52) in fully adjusted models. In contrast, for Whites, significant positive associations existed between carotid plaque and high AC (OR 4.12, 95%CI: 1.29–13.13) and borderline for high CAC (OR 1.83, 95%CI: 0.66–5.19). Conclusions This study demonstrated the presence of carotid plaque appeared to be a marker for AC and potentially CAC in White women during the menopause transition, but not African American middle-aged women. PMID:22037218

  16. Arterial endothelial function measurement method and apparatus

    SciTech Connect

    Maltz, Jonathan S; Budinger, Thomas F

    2014-03-04

    A "relaxoscope" (100) detects the degree of arterial endothelial function. Impairment of arterial endothelial function is an early event in atherosclerosis and correlates with the major risk factors for cardiovascular disease. An artery (115), such as the brachial artery (BA) is measured for diameter before and after several minutes of either vasoconstriction or vasorelaxation. The change in arterial diameter is a measure of flow-mediated vasomodification (FMVM). The relaxoscope induces an artificial pulse (128) at a superficial radial artery (115) via a linear actuator (120). An ultrasonic Doppler stethoscope (130) detects this pulse 10-20 cm proximal to the point of pulse induction (125). The delay between pulse application and detection provides the pulse transit time (PTT). By measuring PTT before (160) and after arterial diameter change (170), FMVM may be measured based on the changes in PTT caused by changes in vessel caliber, smooth muscle tone and wall thickness.

  17. Triple Arterial Phase MR Imaging with Gadoxetic Acid Using a Combination of Contrast Enhanced Time Robust Angiography, Keyhole, and Viewsharing Techniques and Two-Dimensional Parallel Imaging in Comparison with Conventional Single Arterial Phase

    PubMed Central

    Yoon, Jeong Hee; Yu, Mi Hye; Kim, Eun Ju; Han, Joon Koo

    2016-01-01

    Objective To determine whether triple arterial phase acquisition via a combination of Contrast Enhanced Time Robust Angiography, keyhole, temporal viewsharing and parallel imaging can improve arterial phase acquisition with higher spatial resolution than single arterial phase gadoxetic-acid enhanced magnetic resonance imaging (MRI). Materials and Methods Informed consent was waived for this retrospective study by our Institutional Review Board. In 752 consecutive patients who underwent gadoxetic acid-enhanced liver MRI, either single (n = 587) or triple (n = 165) arterial phases was obtained in a single breath-hold under MR fluoroscopy guidance. Arterial phase timing was assessed, and the degree of motion was rated on a four-point scale. The percentage of patients achieving the late arterial phase without significant motion was compared between the two methods using the χ2 test. Results The late arterial phase was captured at least once in 96.4% (159/165) of the triple arterial phase group and in 84.2% (494/587) of the single arterial phase group (p < 0.001). Significant motion artifacts (score ≤ 2) were observed in 13.3% (22/165), 1.2% (2/165), 4.8% (8/165) on 1st, 2nd, and 3rd scans of triple arterial phase acquisitions and 6.0% (35/587) of single phase acquisitions. Thus, the late arterial phase without significant motion artifacts was captured in 96.4% (159/165) of the triple arterial phase group and in 79.9% (469/587) of the single arterial phase group (p < 0.001). Conclusion Triple arterial phase imaging may reliably provide adequate arterial phase imaging for gadoxetic acid-enhanced liver MRI. PMID:27390543

  18. Correlation between angiographic transit times and neurological status on admission in patients with aneurysmal subarachnoid hemorrhage.

    PubMed

    Ivanov, Alexander; Linninger, Andreas; Hsu, Chih-Yang; Amin-Hanjani, Sepideh; Aletich, Victor A; Charbel, Fady T; Alaraj, Ali

    2016-04-01

    OBJECT The use of digital subtraction angiography (DSA) for semiquantitative cerebral blood flow(CBF) assessment is a new technique. The aim of this study was to determine whether patients with aneurysmal subarachnoid hemorrhage (aSAH) with higher Hunt and Hess grades also had higher angiographic contrast transit times (TTs) than patients with lower grades. METHODS A cohort of 30 patients with aSAH and 10 patients without aSAH was included. Relevant clinical information was collected. A method to measure DSA TTs by color-coding reconstructions from DSA contrast-intensity images was applied. Regions of interest (ROIs) were chosen over major cerebral vessels. The estimated TTs included time-to-peak from 0% to 100% (TTP0-100), TTP from 25% to 100% (TTP25-100), and TT from 100% to 10% (TT100-10) contrast intensities. Statistical analysis was used to compare TTs between Group A (Hunt and Hess Grade I-II), Group B (Hunt and Hess Grade III-IV), and the control group. The correlation coefficient was calculated between different ROIs in aSAH groups. RESULTS There was no difference in demographic factors between Group A (n = 10), Group B (n = 20), and the control group (n = 10). There was a strong correlation in all TTs between ROIs in the middle cerebral artery (M1, M2) and anterior cerebral artery (A1, A2). There was a statistically significant difference between Groups A and B in all TT parameters for ROIs. TT100-10 values in the control group were significantly lower than the values in Group B. CONCLUSIONS The DSA TTs showed significant correlation with Hunt and Hess grades. TT delays appear to be independent of increased intracranial pressure and may be an indicator of decreased CBF in patients with a higher Hunt and Hess grade. This method may serve as an indirect technique to assess relative CBF in the angiography suite. PMID:26452118

  19. RSRM Chamber Pressure Oscillations: Transit Time Models and Unsteady CFD

    NASA Technical Reports Server (NTRS)

    Nesman, Tom; Stewart, Eric

    1996-01-01

    Space Shuttle solid rocket motor low frequency internal pressure oscillations have been observed since early testing. The same type of oscillations also are present in the redesigned solid rocket motor (RSRM). The oscillations, which occur during RSRM burn, are predominantly at the first three motor cavity longitudinal acoustic mode frequencies. Broadband flow and combustion noise provide the energy to excite these modes at low levels throughout motor burn, however, at certain times during burn the fluctuating pressure amplitude increases significantly. The increased fluctuations at these times suggests an additional excitation mechanism. The RSRM has inhibitors on the propellant forward facing surface of each motor segment. The inhibitors are in a slot at the segment field joints to prevent burning at that surface. The aft facing segment surface at a field joint slot burns and forms a cavity of time varying size. Initially the inhibitor is recessed in the field joint cavity. As propellant burns away the inhibitor begins to protrude into the bore flow. Two mechanisms (transit time models) that are considered potential pressure oscillation excitations are cavity-edge tones, and inhibitor hole-tones. Estimates of frequency variation with time of longitudinal acoustic modes, cavity edge-tones, and hole-tones compare favorably with frequencies measured during motor hot firing. It is believed that the highest oscillation amplitudes occur when vortex shedding frequencies coincide with motor longitudinal acoustic modes. A time accurate computational fluid dynamic (CFD) analysis was made to replicate the observations from motor firings and to observe the transit time mechanisms in detail. FDNS is the flow solver used to detail the time varying aspects of the flow. The fluid is approximated as a single-phase ideal gas. The CFD model was an axisymmetric representation of the RSRM at 80 seconds into burn.Deformation of the inhibitors by the internal flow was determined

  20. Transit Timing Variations for Inclined and Retrograde Exoplanetary Systems

    NASA Astrophysics Data System (ADS)

    Payne, Matthew J.; Ford, Eric B.; Veras, Dimitri

    2010-03-01

    We perform numerical calculations of the expected transit timing variations (TTVs) induced on a hot-Jupiter by an Earth-mass perturber. Motivated by the recent discoveries of retrograde transiting planets, we concentrate on an investigation of the effect of varying relative planetary inclinations, up to and including completely retrograde systems. We find that planets in low-order (e.g., 2:1) mean-motion resonances (MMRs) retain approximately constant TTV amplitudes for 0° < i < 170°, only reducing in amplitude for i>170°. Systems in higher order MMRs (e.g., 5:1) increase in TTV amplitude as inclinations increase toward 45°, becoming approximately constant for 45° < i < 135°, and then declining for i>135°. Planets away from resonance slowly decrease in TTV amplitude as inclinations increase from 0° to 180°, whereas planets adjacent to resonances can exhibit a huge range of variability in TTV amplitude as a function of both eccentricity and inclination. For highly retrograde systems (135° < i <= 180°), TTV signals will be undetectable across almost the entirety of parameter space, with the exceptions occurring when the perturber has high eccentricity or is very close to an MMR. This high inclination decrease in TTV amplitude (on and away from resonance) is important for the analysis of the known retrograde and multi-planet transiting systems, as inclination effects need to be considered if TTVs are to be used to exclude the presence of any putative planetary companions: absence of evidence is not evidence of absence.

  1. Iterative Bayesian Estimation of Travel Times on Urban Arterials: Fusing Loop Detector and Probe Vehicle Data

    PubMed Central

    Cui, Meng-Ying; Cao, Peng; Wang, Jiang-Bo

    2016-01-01

    On urban arterials, travel time estimation is challenging especially from various data sources. Typically, fusing loop detector data and probe vehicle data to estimate travel time is a troublesome issue while considering the data issue of uncertain, imprecise and even conflicting. In this paper, we propose an improved data fusing methodology for link travel time estimation. Link travel times are simultaneously pre-estimated using loop detector data and probe vehicle data, based on which Bayesian fusion is then applied to fuse the estimated travel times. Next, Iterative Bayesian estimation is proposed to improve Bayesian fusion by incorporating two strategies: 1) substitution strategy which replaces the lower accurate travel time estimation from one sensor with the current fused travel time; and 2) specially-designed conditions for convergence which restrict the estimated travel time in a reasonable range. The estimation results show that, the proposed method outperforms probe vehicle data based method, loop detector based method and single Bayesian fusion, and the mean absolute percentage error is reduced to 4.8%. Additionally, iterative Bayesian estimation performs better for lighter traffic flows when the variability of travel time is practically higher than other periods. PMID:27362654

  2. Iterative Bayesian Estimation of Travel Times on Urban Arterials: Fusing Loop Detector and Probe Vehicle Data.

    PubMed

    Liu, Kai; Cui, Meng-Ying; Cao, Peng; Wang, Jiang-Bo

    2016-01-01

    On urban arterials, travel time estimation is challenging especially from various data sources. Typically, fusing loop detector data and probe vehicle data to estimate travel time is a troublesome issue while considering the data issue of uncertain, imprecise and even conflicting. In this paper, we propose an improved data fusing methodology for link travel time estimation. Link travel times are simultaneously pre-estimated using loop detector data and probe vehicle data, based on which Bayesian fusion is then applied to fuse the estimated travel times. Next, Iterative Bayesian estimation is proposed to improve Bayesian fusion by incorporating two strategies: 1) substitution strategy which replaces the lower accurate travel time estimation from one sensor with the current fused travel time; and 2) specially-designed conditions for convergence which restrict the estimated travel time in a reasonable range. The estimation results show that, the proposed method outperforms probe vehicle data based method, loop detector based method and single Bayesian fusion, and the mean absolute percentage error is reduced to 4.8%. Additionally, iterative Bayesian estimation performs better for lighter traffic flows when the variability of travel time is practically higher than other periods. PMID:27362654

  3. Retrospective study of threshold time for the conventional treatment of branch retinal artery occlusion

    PubMed Central

    Muramatsu, Daisuke; Minezaki, Teruumi; Tsubota, Kinya; Wakabayashi, Yoshihiro; Goto, Hiroshi

    2014-01-01

    Purpose To investigate the medical backgrounds of patients and the treatment periods from the onset of branch retinal artery occlusion to obtaining improved final visual acuity. Methods This was a retrospective case series study. A total of 68 consecutive patients (69 eyes) with branch retinal artery occlusion who visited Tokyo Medical University Hospital from 2007 to 2012 were included in this study. All patients underwent ophthalmic examinations and visual acuity tests. We reviewed their medical records for systemic conditions, as well as the periods from onset of symptoms to treatment. Participants were categorized into 2 groups: group A (n=36), which received any treatment within 24 hours from onset, and group B (n=33), which visited our hospital after 24 hours from onset. Best corrected visual acuity (BCVA) changes from the first to final visit and the relationships between systemic condition and visiting time to BCVA were assessed. Results At the first visit, 59% of the patients had BCVA over 20/40; the ratio was increased to 74% at the final visit. BCVA improved more than 2 lines for 35% of the patients and was unchanged for 57% of those receiving conventional treatment. BCVA over 20/40 was significantly lower in hyperlipidemia patients. Hypertension, diabetes mellitus, and significant carotid stenosis were not correlated. The mean BCVA at baseline (0.91±1.03) significantly recovered to 0.35±0.91 after treatment in group A (P<0.001, Student’s t-test). The mean BCVA at baseline (0.30±0.64) was 0.25±0.61 at the final visit in group B (no significant change). Conclusion Conventional treatment within 24 hours from onset was acceptable for branch retinal artery occlusion. PMID:25284974

  4. Transit times of baseflow in New Zealand rivers

    NASA Astrophysics Data System (ADS)

    Morgenstern, Uwe; Stewart, Mike; Daughney, Chris; Townsend, Dougal

    2015-04-01

    Water quantity and quality responses of catchments to climate and land-use changes are difficult to understand and predict due to complexities of subsurface water flow paths and potentially large groundwater stores. It is difficult to relate the hydrologic responses of catchments to measurable catchment properties. Tritium is ideally suited to provide a measurable parameter of hydrologic response. Tritium, a component of meteoric water, decays with a half-life of 12.32 years after the water enters the groundwater system, and can therefore provide information on transit time of water through the groundwater system over the time range 0 to 200 years mean residence time (MRT). Transit time of the water discharge is one of the most crucial parameters for understanding the response of catchments. In recent years it has become possible to use tritium in a straightforward way for dating of stream and river water due to the decay of the bomb-tritium from atmospheric thermo-nuclear weapons testing, and to improved measurement accuracy for the extremely low natural tritium concentrations. Tritium dating of river water during baseflow conditions from over 120 sites throughout New Zealand show consistent patterns and a good correlation between geology and residence times of the water discharges. Basement rock catchments (greywacke, schist) have very young water of MRT less than 1year, sand-, mud-, limestone catchments have moderately old water of MRT 3-15 years, and porous ignimbrite catchments have very old water of MRT greater than 100 years. For example, the tritium data indicate MRT of 6 - 7 years in the Whanganui River, 3 - 3.5 years in the Rangitikei River, and 9 - 11 years in the large discharges from the Tertiary sediments in the Manawatu catchment. The discharges from the greywacke Ruahine and Tararua Ranges contain very young water with MRT of 0 - 2 years. Associated groundwater stores for the Rangitikei, Manawatu, and Whanganui Rivers are 1, 2, and 5 x 109 m3 of

  5. Toward a Smartphone Application for Estimation of Pulse Transit Time.

    PubMed

    Liu, He; Ivanov, Kamen; Wang, Yadong; Wang, Lei

    2015-01-01

    Pulse transit time (PTT) is an important physiological parameter that directly correlates with the elasticity and compliance of vascular walls and variations in blood pressure. This paper presents a PTT estimation method based on photoplethysmographic imaging (PPGi). The method utilizes two opposing cameras for simultaneous acquisition of PPGi waveform signals from the index fingertip and the forehead temple. An algorithm for the detection of maxima and minima in PPGi signals was developed, which includes technology for interpolation of the real positions of these points. We compared our PTT measurements with those obtained from the current methodological standards. Statistical results indicate that the PTT measured by our proposed method exhibits a good correlation with the established method. The proposed method is especially suitable for implementation in dual-camera-smartphones, which could facilitate PTT measurement among populations affected by cardiac complications. PMID:26516861

  6. Toward a Smartphone Application for Estimation of Pulse Transit Time

    PubMed Central

    Liu, He; Ivanov, Kamen; Wang, Yadong; Wang, Lei

    2015-01-01

    Pulse transit time (PTT) is an important physiological parameter that directly correlates with the elasticity and compliance of vascular walls and variations in blood pressure. This paper presents a PTT estimation method based on photoplethysmographic imaging (PPGi). The method utilizes two opposing cameras for simultaneous acquisition of PPGi waveform signals from the index fingertip and the forehead temple. An algorithm for the detection of maxima and minima in PPGi signals was developed, which includes technology for interpolation of the real positions of these points. We compared our PTT measurements with those obtained from the current methodological standards. Statistical results indicate that the PTT measured by our proposed method exhibits a good correlation with the established method. The proposed method is especially suitable for implementation in dual-camera-smartphones, which could facilitate PTT measurement among populations affected by cardiac complications. PMID:26516861

  7. Wall shear stress calculations in space-time finite element computation of arterial fluid-structure interactions

    NASA Astrophysics Data System (ADS)

    Takizawa, Kenji; Moorman, Creighton; Wright, Samuel; Christopher, Jason; Tezduyar, Tayfun E.

    2009-10-01

    The stabilized space-time fluid-structure interaction (SSTFSI) technique was applied to arterial FSI problems soon after its development by the Team for Advanced Flow Simulation and Modeling. The SSTFSI technique is based on the Deforming-Spatial-Domain/Stabilized Space-Time (DSD/SST) formulation and is supplemented with a number of special techniques developed for arterial FSI. The special techniques developed in the recent past include a recipe for pre-FSI computations that improve the convergence of the FSI computations, using an estimated zero-pressure arterial geometry, Sequentially Coupled Arterial FSI technique, using layers of refined fluid mechanics mesh near the arterial walls, and a special mapping technique for specifying the velocity profile at inflow boundaries with non-circular shape. In this paper we introduce some additional special techniques, related to the projection of fluid-structure interface stresses, calculation of the wall shear stress (WSS), and calculation of the oscillatory shear index. In the test computations reported here, we focus on WSS calculations in FSI modeling of a patient-specific middle cerebral artery segment with aneurysm. Two different structural mechanics meshes and three different fluid mechanics meshes are tested to investigate the influence of mesh refinement on the WSS calculations.

  8. The Timing of School Transitions and Early Adolescent Problem Behavior

    ERIC Educational Resources Information Center

    Lippold, Melissa A.; Powers, Christopher J.; Syvertsen, Amy K.; Feinberg, Mark E.; Greenberg, Mark T.

    2013-01-01

    This longitudinal study investigates whether rural adolescents who transition to a new school in sixth grade have higher levels of risky behavior than adolescents who transition in seventh grade. Our findings indicate that later school transitions had little effect on problem behavior between sixth and ninth grades. Cross-sectional analyses found…

  9. Factors influencing stream water transit times in tropical montane watersheds

    NASA Astrophysics Data System (ADS)

    Muñoz-Villers, L. E.; Geissert, D. R.; Holwerda, F.; McDonnell, J. J.

    2015-10-01

    Stream water mean transit time (MTT) is a fundamental hydrologic parameter that integrates the distribution of sources, flow paths and storages present in catchments. However, in the tropics little MTT work has been carried out, despite its usefulness for providing important information on watershed functioning at different spatial scales in (largely) ungauged basins. In particular, very few studies have quantified stream MTTs and related to catchment characteristics in tropical montane regions. Here we examined topographic, land use/cover and soil hydraulic controls on baseflow transit times for nested watersheds (0.1-34 km2) within a humid mountainous region, underlain by volcanic soil (Andisols) in central Veracruz (eastern Mexico). We used a 2 year record of bi-weekly isotopic composition of precipitation and stream baseflow data to estimate MTT. Land use/cover and topographic parameters (catchment area and form, drainage density, slope gradient and length) were derived from GIS analysis. Soil water retention characteristics, and depth and permeability of the soil-bedrock interface were obtained from intensive field measurements and laboratory analysis. Results showed that baseflow MTT ranged between 1.2 and 2.7 years across the 12 study catchments. Overall, MTTs across scales were mainly controlled by catchment slope and the permeability observed at the soil-bedrock interface. In association with topography, catchment form, land cover and the depth to the soil-bedrock interface were also identified as important features influencing baseflow MTTs. The greatest differences in MTTs were found at the smallest (0.1-1.5 km2) and the largest scales (14-34 km2). Interestingly, longest stream MTTs were found in the headwater cloud forest catchments.

  10. Factors influencing stream baseflow transit times in tropical montane watersheds

    NASA Astrophysics Data System (ADS)

    Muñoz-Villers, Lyssette E.; Geissert, Daniel R.; Holwerda, Friso; McDonnell, Jeffrey J.

    2016-04-01

    Stream water mean transit time (MTT) is a fundamental hydrologic parameter that integrates the distribution of sources, flow paths, and storages present in catchments. However, in the tropics little MTT work has been carried out, despite its usefulness for providing important information on watershed functioning at different spatial scales in (largely) ungauged basins. In particular, very few studies have quantified stream MTTs or have related these to catchment characteristics in tropical montane regions. Here we examined topographic, land use/cover and soil hydraulic controls on baseflow transit times for nested catchments (0.1-34 km2) within a humid mountainous region, underlain by volcanic soil (Andisols) in central Veracruz (eastern Mexico). We used a 2-year record of bi-weekly isotopic composition of precipitation and stream baseflow data to estimate MTT. Land use/cover and topographic parameters (catchment area and form, drainage density, slope gradient and length) were derived from geographic information system (GIS) analysis. Soil water retention characteristics, and depth and permeability of the soil-bedrock interface were obtained from intensive field measurements and laboratory analysis. Results showed that baseflow MTTs ranged between 1.2 and 2.7 years across the 12 study catchments. Overall, MTTs across scales were mainly controlled by catchment slope and the permeability observed at the soil-bedrock interface. In association with topography, catchment form and the depth to the soil-bedrock interface were also identified as important features influencing baseflow MTTs. The greatest differences in MTTs were found both within groups of small (0.1-1.5 km2) and large (14-34 km2) catchments. Interestingly, the longest stream MTTs were found in the headwater cloud forest catchments.

  11. Optimization of the deflagration to detonation transition: reduction of length and time of transition

    NASA Astrophysics Data System (ADS)

    Sorin, R.; Zitoun, R.; Desbordes, D.

    2006-06-01

    The aim of this experimental investigation is the study of Deflagration to Detonation Transition (DDT) in tubes in order to (i) reduce both run-up distance and time of transition ( L DDT and t DDT) in connection with Pulsed Detonation Engine applications and to (ii) attempt to scale L DDT with λCJ (the detonation cellular structure width). In DDT, the production of turbulence during the long flame run-up can lead to L DDT values of several meters. To shorten L DDT, an experimental set-up is designed to quickly induce highly turbulent initial flow. It consists of a double chamber terminated with a perforated plate of high Blockage Ratio (BR) positioned at the beginning of a 26 mm inner diameter tube containing a “Shchelkin spiral” of BR ≈ 0.5. The study involves stoichiometric reactive mixtures of H2, CH4, C3H8, and C2H4 with oxygen and diluted with N2 in order to obtain the same cell width λCJ≈10 mm at standard conditions. The results show that a shock-flame system propagating with nearly the isobaric speed of sound of combustion products, called the choking regime, is rapidly obtained. This experimental set-up allows a L DDT below 40 cm for the mixtures used and a ratio L DDT/λCJ ranging from 23 to 37. The transition distance seems to depend on the reduced activation energy ( E a/ RT c) and on the normalized heat of reaction ( Q/ a 0 2). The higher these quantities are, the shorter the ratio L DDT/λCJ is.

  12. Acute Appendicitis as Complication of Colon Transit Time Study; A Case Report

    PubMed Central

    Ghahramani, Leila; Roshanravan, Reza; Khodaei, Shahin; Rahimi Kazerooni, Salar; Moslemi, Sam

    2015-01-01

    Colon transit time study with radio opaque markers is a simple method for assessment of colon motility disorder in patients with chronic idiopathic constipation. We report a case of acute appendicitis that was induced by impaction of radio opaque markers after colon transit time study. We think that this case report is first significant complication of colon transit time study until now PMID:26396723

  13. Remotely detected differential pulse transit time as a stress indicator

    NASA Astrophysics Data System (ADS)

    Kaur, Balvinder; Tarbox, Elizabeth; Cissel, Marty; Moses, Sophia; Luthra, Megha; Vaidya, Misha; Tran, Nhien; Ikonomidou, Vasiliki N.

    2015-05-01

    The human cardiovascular system, controlled by the autonomic nervous system (ANS), is one of the first sites where one can see the "fight-or-flight" response due to the presence of external stressors. In this paper, we investigate the possibility of detecting mental stress using a novel measure that can be measured in a contactless manner: Pulse transit time (dPTT), which refers to the time that is required for the blood wave (BW) to cover the distance from the heart to a defined remote location in the body. Loosely related to blood pressure, PTT is a measure of blood velocity, and is also implicated in the "fight-or-flight" response. We define the differential PTT (dPTT) as the difference in PTT between two remote areas of the body, such as the forehead and the palm. Expanding our previous work on remote BW detection from visible spectrum videos, we built a system that remotely measures dPTT. Human subject data were collected under an IRB approved protocol from 15 subjects both under normal and stress states and are used to initially establish the potential use of remote dPPT detection as a stress indicator.

  14. A Wearable Vital Signs Monitor at the Ear for Continuous Heart Rate and Pulse Transit Time Measurements

    PubMed Central

    Winokur, Eric S.; Da He, David; Sodini, Charles G.

    2015-01-01

    A continuous, wearable and wireless vital signs monitor at the ear is demonstrated. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. The device monitors the electrocardiogram (ECG) in a single lead configuration, the ballistocardiogram (BCG) with a MEMS triaxial accelerometer, and the photoplethysmograms (PPG) with 660nm and 940nm LED sources and a static photocurrent subtraction analog front end. Clinical tests are conducted, including Valsalva and head-up tilt maneuvers. Peak timing intervals between the ECG, BCG and PPG are extracted and are shown to relate to pre-ejection period and mean arterial blood pressure (MAP). Pulse Transit Time (PTT) extracted from cross-correlation between the PPG and BCG shows improved results compared to the pulse arrival time (PAT) method for tracking changes in MAP. PMID:23366488

  15. Understanding Time in Learning Transitions through the Lifecourse

    ERIC Educational Resources Information Center

    Colley, Helen

    2007-01-01

    Policy-makers in the UK and Europe have become concerned with the successful management of transitions in learning as a means of increasing the competitiveness of their economies. Transitions relating to informal as well as formal learning have also been an important focus for the sociology of education. In this paper, I review alternative ways in…

  16. A Catalog of Transit Timing Posterior Distributions for all Kepler Planet Candidate Events

    NASA Astrophysics Data System (ADS)

    Montet, Benjamin Tyler; Becker, Juliette C.; Johnson, John

    2015-08-01

    Kepler has ushered in a new era of planetary dynamics, enabling the detection of interactions between multiple planets in transiting systems for hundreds of systems. These interactions, observed as transit timing variations (TTVs), have been used to find non-transiting companions to transiting systems and to measure masses, eccentricities, and inclinations of transiting planets. Often, physical parameters are inferred by comparing the observed light curve to the result of a photodynamical model, a time-intensive process that often ignores the effects of correlated noise in the light curve. Catalogs of transit timing observations have previously neglected non-Gaussian uncertainties in the times of transit, uncertainties in the transit shape, and short cadence data. Here, we present a catalog of not only times of transit centers, but also posterior distributions on the time of transit for every planet candidate transit event in the Kepler data, developed through importance sampling of each transit. This catalog allows us to marginalize over uncertainties in the transit shape and incorporate short cadence data, the effects of correlated noise, and non-Gaussian posteriors. Our catalog will enable dynamical studies that reflect accurately the precision of Kepler and its limitations without requiring the computational power to model the light curve completely with every integration.

  17. Conductivity and transit time estimates of a soil liner

    USGS Publications Warehouse

    Krapac, I.G.; Cartwright, K.; Panno, S.V.; Hensel, B.R.; Rehfeldt, K.H.; Herzog, B.L.

    1990-01-01

    A field-scale soil linear was built to assess the feasibilty of constructing a liner to meet the saturated hydraulic conductivity requirement of the U.S. EPA (i.e., less than 1 ?? 10-7 cm/s), and to determine the breakthrough and transit times of water and tracers through the liner. The liner, 8 ?? 15 ?? 0.9 m, was constructed in 15-cm compacted lifts using a 20,037-kg pad-foot compactor and standard engineering practices. Estimated saturated hydraulic conductivities were 2.4 ?? 10-9 cm/s, based on data from large-ring infiltrometers; 4.0 ?? 10-8 cm/s from small-ring infiltrometers; and 5.0 ?? 10-8 cm/s from a water-balance analysis. These estimates were derived from 1 year of monitoring water infiltration into the linear. Breakthrough of tracers at the base of the liner was estimated to be between 2 and 13 years, depending on the method of calculation and the assumptions used in the calculation.

  18. Modeling hyporheic exchange and in-stream transport with time-varying transit time distributions

    NASA Astrophysics Data System (ADS)

    Ball, A.; Harman, C. J.; Ward, A. S.

    2014-12-01

    Transit time distributions (TTD) are used to understand in-stream transport and exchange with the hyporheic zone by quantifying the probability of water (and of dissolved material) taking time T to traverse the stream reach control volume. However, many studies using this method assume a TTD that is time-invariant, despite the time-variability of the streamflow. Others assume that storage is 'randomly sampled' or 'well-mixed' with a fixed volume or fixed exchange rate. Here we present a formulation for a time-variable TTD that relaxes both the time-invariant and 'randomly sampled' assumptions and only requires a few parameters. The framework is applied to transient storage, representing some combination of in-stream and hyporheic storage, along a stream reach. This approach does not assume that hyporheic and dead-zone storage is fixed or temporally-invariant, and allows for these stores to be sampled in more physically representative ways determined by the system itself. Instead of using probability distributions of age, probability distributions of storage (ranked by age) called Ω functions are used to describe how the off-stream storage is sampled in the outflow. Here the Ω function approach is used to describe hyporheic exchange during diurnal fluctuations in streamflow in a gaining reach of the H.J. Andrews Experimental Forest. The breakthrough curves of salt slugs injected four hours apart over a 28-hour period show a systematic variation in transit time distribution. This new approach allows us to relate these salt slug TTDs to a corresponding time-variation in the Ω function, which can then be related to changes in in-stream storage and hyporheic zone mobilization under varying flow conditions. Thus, we can gain insights into how channel storage and hyporheic exchange are changing through time without having to specify difficult to measure or unmeasurable quantities of our system, such as total storage.

  19. A Gaussian Model-Based Probabilistic Approach for Pulse Transit Time Estimation.

    PubMed

    Jang, Dae-Geun; Park, Seung-Hun; Hahn, Minsoo

    2016-01-01

    In this paper, we propose a new probabilistic approach to pulse transit time (PTT) estimation using a Gaussian distribution model. It is motivated basically by the hypothesis that PTTs normalized by RR intervals follow the Gaussian distribution. To verify the hypothesis, we demonstrate the effects of arterial compliance on the normalized PTTs using the Moens-Korteweg equation. Furthermore, we observe a Gaussian distribution of the normalized PTTs on real data. In order to estimate the PTT using the hypothesis, we first assumed that R-waves in the electrocardiogram (ECG) can be correctly identified. The R-waves limit searching ranges to detect pulse peaks in the photoplethysmogram (PPG) and to synchronize the results with cardiac beats--i.e., the peaks of the PPG are extracted within the corresponding RR interval of the ECG as pulse peak candidates. Their probabilities of being the actual pulse peak are then calculated using a Gaussian probability function. The parameters of the Gaussian function are automatically updated when a new pulse peak is identified. This update makes the probability function adaptive to variations of cardiac cycles. Finally, the pulse peak is identified as the candidate with the highest probability. The proposed approach is tested on a database where ECG and PPG waveforms are collected simultaneously during the submaximal bicycle ergometer exercise test. The results are promising, suggesting that the method provides a simple but more accurate PTT estimation in real applications. PMID:25420274

  20. Cuff-Free Blood Pressure Estimation Using Pulse Transit Time and Heart Rate

    PubMed Central

    Wang, Ruiping; Jia, Wenyan; Mao, Zhi-Hong; Sclabassi, Robert J.

    2015-01-01

    It has been reported that the pulse transit time (PTT), the interval between the peak of the R-wave in electrocardiogram (ECG) and the fingertip photoplethysmogram (PPG), is related to arterial stiffness, and can be used to estimate the systolic blood pressure (SBP) and diastolic blood pressure (DBP). This phenomenon has been used as the basis to design portable systems for continuously cuff-less blood pressure measurement, benefiting numerous people with heart conditions. However, the PTT-based blood pressure estimation may not be sufficiently accurate because the regulation of blood pressure within the human body is a complex, multivariate physiological process. Considering the negative feedback mechanism in the blood pressure control, we introduce the heart rate (HR) and the blood pressure estimate in the previous step to obtain the current estimate. We validate this method using a clinical database. Our results show that the PTT, HR and previous estimate reduce the estimated error significantly when compared to the conventional PTT estimation approach (p<0.05). PMID:26213717

  1. Characterization of polymers in the glass transition range: Time-temperature and time-aging time superposition in polycarbonate

    SciTech Connect

    Pesce, J.J.; Niemiec, J.M.; Chiang, M.Y.

    1995-12-31

    Here we present time-temperature and time-aging time superposition data for a commercial grade polycarbonate. The data reduction is performed for dynamic-mechanical data obtained in torsion over a range of temperatures from 103.6 to 144.5{degrees}C and aging times to 16 h. For time-temperature superposition the results show the deviation of the sub-T{sub g} response from the WTF equation. Two response regimes are observed: at temperatures far below T{sub g} the log(a{sub T}) is linear in T, followed by a transition towards the WLF behavior as T{sub g} is approached. The temperature at which the behavior changes from a linear dependence of log(aT) on T to the transition-type behavior is found to depend on the aging time. This temperature decreases as aging time increases. The time-aging time response is found to behave in a normal way. At temperatures far below T{sub g} the log(a{sub te}) vs log(t{sub e}) is constant and has a slope somewhat less than unity. However, nearer to T{sub g} the slope decreases and there is a second regime in which the aging virtually ceases. In this polycarbonate, above 136.9{degrees}C, no aging is observed.

  2. Time from symptoms to definitive diagnosis of idiopathic pulmonary arterial hypertension: The delay study.

    PubMed

    Strange, Geoff; Gabbay, Eli; Kermeen, Fiona; Williams, Trevor; Carrington, Melinda; Stewart, Simon; Keogh, Anne

    2013-01-01

    Survival rates for patients with idiopathic pulmonary arterial hypertension (IPAH) have improved with the introduction of PAH-specific therapies. However, the time between patient-reported onset of symptoms and a definitive diagnosis of IPAH is consistently delayed. We conducted a retrospective, multi-center, descriptive investigation in order to (a) understand what factors contribute to persistent diagnostic delays, and (b) examine the time from initial symptom onset to a definitive diagnosis of IPAH. Between January 2007 and December 2008, we enrolled consecutively diagnosed adults with IPAH from four tertiary referral centers in Australia. Screening of patient records and "one-on-one" interviews were used to determine the time from patient-described initial symptoms to a diagnosis of IPAH, confirmed by right heart catheterization (RHC). Thirty-two participants (69% female) were studied. Mean age at symptom onset was 56 ± 16.4 years and 96% reported exertional dyspnea. Mean time from symptom onset to diagnosis was 47 ± 34 months with patients subsequently aged 60 ± 17.3 years. Patients reported 5.3 ± 3.8 GP visits and 3.0 ± 2.1 specialist reviews before being seen at a pulmonary hypertension (PH) center. Advanced age, number of general practitioner (GP) visits, heart rate, and systolic blood pressure at the time of diagnosis were significantly associated with the observed delay. We found a significant delay of 3.9 years from symptom onset to a diagnosis of IPAH in Australia. Exertional dyspnea is the most common presenting symptom. Current practice within Australia does not appear to have the specific capacity for timely, multi-factorial evaluation of breathlessness and potential IPAH. PMID:23662179

  3. Time from symptoms to definitive diagnosis of idiopathic pulmonary arterial hypertension: The delay study

    PubMed Central

    Strange, Geoff; Gabbay, Eli; Kermeen, Fiona; Williams, Trevor; Carrington, Melinda; Stewart, Simon; Keogh, Anne

    2013-01-01

    Survival rates for patients with idiopathic pulmonary arterial hypertension (IPAH) have improved with the introduction of PAH-specific therapies. However, the time between patient-reported onset of symptoms and a definitive diagnosis of IPAH is consistently delayed. We conducted a retrospective, multi-center, descriptive investigation in order to (a) understand what factors contribute to persistent diagnostic delays, and (b) examine the time from initial symptom onset to a definitive diagnosis of IPAH. Between January 2007 and December 2008, we enrolled consecutively diagnosed adults with IPAH from four tertiary referral centers in Australia. Screening of patient records and “one-on-one” interviews were used to determine the time from patient-described initial symptoms to a diagnosis of IPAH, confirmed by right heart catheterization (RHC). Thirty-two participants (69% female) were studied. Mean age at symptom onset was 56 ± 16.4 years and 96% reported exertional dyspnea. Mean time from symptom onset to diagnosis was 47 ± 34 months with patients subsequently aged 60 ± 17.3 years. Patients reported 5.3 ± 3.8 GP visits and 3.0 ± 2.1 specialist reviews before being seen at a pulmonary hypertension (PH) center. Advanced age, number of general practitioner (GP) visits, heart rate, and systolic blood pressure at the time of diagnosis were significantly associated with the observed delay. We found a significant delay of 3.9 years from symptom onset to a diagnosis of IPAH in Australia. Exertional dyspnea is the most common presenting symptom. Current practice within Australia does not appear to have the specific capacity for timely, multi-factorial evaluation of breathlessness and potential IPAH. PMID:23662179

  4. Effects of cuff inflation and deflation on pulse transit time measured from ECG and multi-wavelength PPG.

    PubMed

    Liu, Jing; Li, Yao; Ding, Xiao-Rong; Dai, Wen-Xuan; Zhang, Yuan-Ting

    2015-01-01

    Pulse transit time (PTT), which refers to the time it takes a pulse wave to travel between two arterial sites is a promising index for cuff-less blood pressure (BP) estimation, as well as non-invasive assessment of arterial functions. However, it has not been investigated whether PTTs measured from ECG and different wavelength PPG are equally affected by the arterial status. Furthermore, comparison between the changes of different PTTs can provide enlightenment on the hardware implementation of the PTT-based BP estimation method. This work mainly studied the changes of PTTs calculated from electrocardiogram (ECG) and multi-wavelength photoplethysmogram (PPG) after exerting cuff pressure on the upper arm. A four-channel PPG acquisition system was developed to collect the multi-wavelength PPG signals of red, yellow, green and blue light at the fingertip simultaneously. Ten subjects participated in the experiment and their PTTs measured from different PPG and ECG signals before and after exerting cuff pressure were compared. This study found that within one minute after the four-minute cuff inflation and deflation process, the PTT measured from ECG and yellow PPG experienced a significant increase (p<;0.05) while the PTT from ECG and blue PPG had no statistical difference (p>0.9) compared with that before exerting cuff pressure. This indicates that PTTs calculated from different wavelength PPG have different recoverability from smooth muscle relaxation. Another interesting finding is that the PTT calculated from ECG and yellow PPG had a strong correlation (|r|>0.7) with the time difference between yellow PPG and other PPG signals, which implies the potential of the time difference between yellow PPG and other PPGs as a complementary to PTT-based model for blood pressure estimation. PMID:26737652

  5. Timing is everything : along the fossil fuel transition pathway.

    SciTech Connect

    Kobos, Peter Holmes; Walker, La Tonya Nicole; Malczynski, Leonard A.

    2013-10-01

    People save for retirement throughout their career because it is virtually impossible to save all you'll need in retirement the year before you retire. Similarly, without installing incremental amounts of clean fossil, renewable or transformative energy technologies throughout the coming decades, a radical and immediate change will be near impossible the year before a policy goal is set to be in place. Therefore, our research question is,To meet our desired technical and policy goals, what are the factors that affect the rate we must install technology to achieve these goals in the coming decades?' Existing models do not include full regulatory constraints due to their often complex, and inflexible approaches to solve foroptimal' engineering instead ofrobust' and multidisciplinary solutions. This project outlines the theory and then develops an applied software tool to model the laboratory-to-market transition using the traditional technology readiness level (TRL) framework, but develops subsequent and a novel regulatory readiness level (RRL) and market readiness level (MRL). This tool uses the ideally-suited system dynamics framework to incorporate feedbacks and time delays. Future energy-economic-environment models, regardless of their programming platform, may adapt this software model component framework ormodule' to further vet the likelihood of new or innovative technology moving through the laboratory, regulatory and market space. The prototype analytical framework and tool, called the Technology, Regulatory and Market Readiness Level simulation model (TRMsim) illustrates the interaction between technology research, application, policy and market dynamics as they relate to a new or innovative technology moving from the theoretical stage to full market deployment. The initial results that illustrate the model's capabilities indicate for a hypothetical technology, that increasing the key driver behind each of the TRL, RRL and

  6. Measurement of vascular water transport in human subjects using time-resolved pulsed arterial spin labelling.

    PubMed

    Bibic, Adnan; Knutsson, Linda; Schmidt, Anders; Henningsson, Erik; Månsson, Sven; Abul-Kasim, Kasim; Åkeson, Jonas; Gunther, Matthias; Ståhlberg, Freddy; Wirestam, Ronnie

    2015-08-01

    Most approaches to arterial spin labelling (ASL) data analysis aim to provide a quantitative measure of the cerebral blood flow (CBF). This study, however, focuses on the measurement of the transfer time of blood water through the capillaries to the parenchyma (referred to as the capillary transfer time, CTT) as an alternative parameter to characterise the haemodynamics of the system. The method employed is based on a non-compartmental model, and no measurements need to be added to a common time-resolved ASL experiment. Brownian motion of labelled spins in a potential was described by a one-dimensional general Langevin equation as the starting point, and as a Fokker-Planck differential equation for the averaged distribution of labelled spins at the end point, which takes into account the effects of flow and dispersion of labelled water by the pseudorandom nature of the microvasculature and the transcapillary permeability. Multi-inversion time (multi-TI) ASL data were acquired in 14 healthy subjects on two occasions in a test-retest design, using a pulsed ASL sequence and three-dimensional gradient and spin echo (3D-GRASE) readout. Based on an error analysis to predict the size of a region of interest (ROI) required to obtain reasonably precise parameter estimates, data were analysed in two relatively large ROIs, i.e. the occipital lobe (OC) and the insular cortex (IC). The average values of CTT in OC were 260 ± 60 ms in the first experiment and 270 ± 60 ms in the second experiment. The corresponding IC values were 460 ± 130 ms and 420 ± 139 ms, respectively. Information related to the water transfer time may be important for diagnostics and follow-up of cerebral conditions or diseases characterised by a disrupted blood-brain barrier or disturbed capillary blood flow. PMID:26147641

  7. Photobleaching of arterial fluorescent compounds: characterization of elastin, collagen and cholesterol time-resolved spectra during prolonged ultraviolet irradiation.

    PubMed

    Marcu, L; Grundfest, W S; Maarek, J M

    1999-06-01

    To study the photobleaching of the main fluorescent compounds of the arterial wall, we repeatedly measured the time-resolved fluorescence of elastin, collagen and cholesterol during 560 s of excitation with nitrogen laser pulses. Three fluence rate levels were used: 0.72, 7.25 and 21.75 microW/mm2. The irradiation-related changes of the fluorescence intensity and of the time-resolved fluorescence decay constants were characterized for the emission at 390, 430 and 470 nm. The fluorescence intensity at 390 nm decreased by 25-35% when the fluence delivered was 4 mJ/mm2, a common value in fluorescence studies of the arterial wall. Cholesterol fluorescence photobleached the most, and elastin fluorescence photobleached the least. Photobleaching was most intense at 390 nm and least intense at 470 nm such that the emission spectra of the three compounds were markedly distorted by photobleaching. The time-resolved decay constants and the fluorescence lifetime were not altered by irradiation when the fluence was below 4 mJ/mm2. The spectral distortions associated with photobleaching complicate the interpretation of arterial wall fluorescence in terms of tissue content in elastin, collagen and cholesterol. Use of the time-dependent features of the emission that are not altered by photobleaching should increase the accuracy of arterial wall analysis by fluorescence spectroscopy. PMID:10378012

  8. Biomarkers in Coronary Artery Bypass Surgery: Ready for Prime Time and Outcome Prediction?

    PubMed Central

    Parolari, Alessandro; Poggio, Paolo; Myasoedova, Veronika; Songia, Paola; Bonalumi, Giorgia; Pilozzi, Alberto; Pacini, Davide; Alamanni, Francesco; Tremoli, Elena

    2016-01-01

    Coronary artery bypass surgery (CABG) is still one of the most frequently performed surgical procedures all over the world. The results of this procedure have been constantly improved over the years with low perioperative mortality rates, with relatively low complication rates. To further improve these outstanding results, the clinicians focused their attention at biomarkers as outcome predictors. Although biological testing for disease prediction has already been discussed many times, the role of biomarkers in outcome prediction after CABG is still controversial. In this article, we reviewed the current knowledge regarding the role of genetic and dynamic biomarkers and their possible association with the occurrence of adverse clinical outcomes after CABG. We also took into consideration that the molecular pathway activation and the possible imbalance may affect hard outcomes and graft patency. We analyzed biomarkers classified in two different categories depending on their possibility to change over time: genetic markers and dynamic markers. Moreover, we evaluated these markers by dividing them, into sub-categories, such as inflammation, hemostasis, renin–angiotensin, endothelial function, and other pathways. We showed that biomarkers might be associated with unfavorable outcomes after surgery, and in some cases improved outcome prediction. However, the identification of a specific panel of biomarkers or of some algorithms including biomarkers is still in an early developmental phase. Finally, larger studies are needed to analyze broad panel of biomarkers with the specific aim to evaluate the prediction of hard outcomes and graft patency. PMID:26779491

  9. Primary Pulmonary Artery Sarcoma on Dual-Time Point FDG PET/CT Imaging.

    PubMed

    Li, Juan; Zhao, Qian; He, Lirong; Zhuang, Xiaoqing; Li, Fang

    2016-08-01

    A 59-year-old man presented cough, chest pain, and shortness of breath for 2 weeks and fever for 4 days. A contrast chest CT revealed a large right pulmonary artery filling defect, suggestive of pulmonary embolism that failed to respond to anticoagulation therapy. FDG PET/CT was performed to evaluate possible malignancy, which revealed intense activity in the right main pulmonary artery without any extrathoracic abnormality. The ratio of the SUVmax of this lesion to the liver was significantly increased in the delayed PET images. The pathological examination demonstrated primary pulmonary artery sarcoma. PMID:27163460

  10. Colonic transit time is related to bacterial metabolism and mucosal turnover in the gut.

    PubMed

    Roager, Henrik M; Hansen, Lea B S; Bahl, Martin I; Frandsen, Henrik L; Carvalho, Vera; Gøbel, Rikke J; Dalgaard, Marlene D; Plichta, Damian R; Sparholt, Morten H; Vestergaard, Henrik; Hansen, Torben; Sicheritz-Pontén, Thomas; Nielsen, H Bjørn; Pedersen, Oluf; Lauritzen, Lotte; Kristensen, Mette; Gupta, Ramneek; Licht, Tine R

    2016-01-01

    Little is known about how colonic transit time relates to human colonic metabolism and its importance for host health, although a firm stool consistency, a proxy for a long colonic transit time, has recently been positively associated with gut microbial richness. Here, we show that colonic transit time in humans, assessed using radio-opaque markers, is associated with overall gut microbial composition, diversity and metabolism. We find that a long colonic transit time associates with high microbial richness and is accompanied by a shift in colonic metabolism from carbohydrate fermentation to protein catabolism as reflected by higher urinary levels of potentially deleterious protein-derived metabolites. Additionally, shorter colonic transit time correlates with metabolites possibly reflecting increased renewal of the colonic mucosa. Together, this suggests that a high gut microbial richness does not per se imply a healthy gut microbial ecosystem and points at colonic transit time as a highly important factor to consider in microbiome and metabolomics studies. PMID:27562254

  11. Transit Monitoring in the South (TraMoS) Project: Discarding Transit Timing Variations in WASP-5b

    NASA Astrophysics Data System (ADS)

    Hoyer, S.; Rojo, P.; López-Morales, M.

    2012-03-01

    We report nine new transit epochs of the extrasolar planet WASP-5b, observed in the Bessell I band with the Southern Astrophysical Research Telescope at the Cerro Pachon Observatory and with the SMARTS 1 m Telescope at the Cerro Tololo Inter-American Observatory, between 2008 August and 2009 October. The new transits have been combined with all previously published transit data for this planet to provide a new Transit Timing Variation (TTV) analysis of its orbit. We find no evidence of TTV rms variations larger than 1 minute over a 3 year time span. This result discards the presence of planets more massive than about 5 M ⊕, 1 M ⊕, and 2 M ⊕ around the 1:2, 5:3, and 2:1 orbital resonances, respectively. These new detection limits exceed by ~5-30 times the limits imposed by current radial velocity observations in the mean motion resonances of this system. Our search for the variation of other parameters, such as orbital inclination and transit depth, also yields negative results over the total time span of the transit observations. This result supports formation theories that predict a paucity of planetary companions to hot Jupiters.

  12. TRANSIT MONITORING IN THE SOUTH (TraMoS) PROJECT: DISCARDING TRANSIT TIMING VARIATIONS IN WASP-5b

    SciTech Connect

    Hoyer, S.; Rojo, P.; Lopez-Morales, M. E-mail: pato@das.uchile.cl

    2012-03-20

    We report nine new transit epochs of the extrasolar planet WASP-5b, observed in the Bessell I band with the Southern Astrophysical Research Telescope at the Cerro Pachon Observatory and with the SMARTS 1 m Telescope at the Cerro Tololo Inter-American Observatory, between 2008 August and 2009 October. The new transits have been combined with all previously published transit data for this planet to provide a new Transit Timing Variation (TTV) analysis of its orbit. We find no evidence of TTV rms variations larger than 1 minute over a 3 year time span. This result discards the presence of planets more massive than about 5 M{sub Circled-Plus }, 1 M{sub Circled-Plus }, and 2 M{sub Circled-Plus} around the 1:2, 5:3, and 2:1 orbital resonances, respectively. These new detection limits exceed by {approx}5-30 times the limits imposed by current radial velocity observations in the mean motion resonances of this system. Our search for the variation of other parameters, such as orbital inclination and transit depth, also yields negative results over the total time span of the transit observations. This result supports formation theories that predict a paucity of planetary companions to hot Jupiters.

  13. Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations

    SciTech Connect

    Steffen, Jason H.; Fabrycky, Daniel C.; Ford, Eric B.; Carter, Joshua A.; Fressin, Francois; Holman, Matthew J.; Lissauer, Jack J.; Rowe, Jason F.; Ragozzine, Darin; Welsh, William F.; Borucki, William J.; /NASA, Ames /UC, Santa Barbara

    2012-01-01

    We present a method to confirm the planetary nature of objects in systems with multiple transiting exoplanet candidates. This method involves a Fourier-domain analysis of the deviations in the transit times from a constant period that result from dynamical interactions within the system. The combination of observed anticorrelations in the transit times and mass constraints from dynamical stability allow us to claim the discovery of four planetary systems, Kepler-25, Kepler-26, Kepler-27 and Kepler-28, containing eight planets and one additional planet candidate.

  14. Decreasing Transition Times in Elementary School Classrooms: Using Computer-Assisted Instruction to Automate Intervention Components

    ERIC Educational Resources Information Center

    Hine, Jeffrey F.; Ardoin, Scott P.; Foster, Tori E.

    2015-01-01

    Research suggests that students spend a substantial amount of time transitioning between classroom activities, which may reduce time spent academically engaged. This study used an ABAB design to evaluate the effects of a computer-assisted intervention that automated intervention components previously shown to decrease transition times. We examined…

  15. Time-Series Interactions of Gene Expression, Vascular Growth and Hemodynamics during Early Embryonic Arterial Development.

    PubMed

    Goktas, Selda; Uslu, Fazil E; Kowalski, William J; Ermek, Erhan; Keller, Bradley B; Pekkan, Kerem

    2016-01-01

    The role of hemodynamic forces within the embryo as biomechanical regulators for cardiovascular morphogenesis, growth, and remodeling is well supported through the experimental studies. Furthermore, clinical experience suggests that perturbed flow disrupts the normal vascular growth process as one etiology for congenital heart diseases (CHD) and for fetal adaptation to CHD. However, the relationships between hemodynamics, gene expression and embryonic vascular growth are poorly defined due to the lack of concurrent, sequential in vivo data. In this study, a long-term, time-lapse optical coherence tomography (OCT) imaging campaign was conducted to acquire simultaneous blood velocity, pulsatile micro-pressure and morphometric data for 3 consecutive early embryonic stages in the chick embryo. In conjunction with the in vivo growth and hemodynamics data, in vitro reverse transcription polymerase chain reaction (RT-PCR) analysis was performed to track changes in transcript expression relevant to histogenesis and remodeling of the embryonic arterial wall. Our non-invasive extended OCT imaging technique for the microstructural data showed continuous vessel growth. OCT data coupled with the PIV technique revealed significant but intermitted increases in wall shear stress (WSS) between first and second assigned stages and a noticeable decrease afterwards. Growth rate, however, did not vary significantly throughout the embryonic period. Among all the genes studied, only the MMP-2 and CASP-3 expression levels remained unchanged during the time course. Concurrent relationships were obtained among the transcriptional modulation of the genes, vascular growth and hemodynamics-related changes. Further studies are indicated to determine cause and effect relationships and reversibility between mechanical and molecular regulation of vasculogenesis. PMID:27552150

  16. Time-Series Interactions of Gene Expression, Vascular Growth and Hemodynamics during Early Embryonic Arterial Development

    PubMed Central

    Goktas, Selda; Uslu, Fazil E.; Kowalski, William J.; Ermek, Erhan; Keller, Bradley B.

    2016-01-01

    The role of hemodynamic forces within the embryo as biomechanical regulators for cardiovascular morphogenesis, growth, and remodeling is well supported through the experimental studies. Furthermore, clinical experience suggests that perturbed flow disrupts the normal vascular growth process as one etiology for congenital heart diseases (CHD) and for fetal adaptation to CHD. However, the relationships between hemodynamics, gene expression and embryonic vascular growth are poorly defined due to the lack of concurrent, sequential in vivo data. In this study, a long-term, time-lapse optical coherence tomography (OCT) imaging campaign was conducted to acquire simultaneous blood velocity, pulsatile micro-pressure and morphometric data for 3 consecutive early embryonic stages in the chick embryo. In conjunction with the in vivo growth and hemodynamics data, in vitro reverse transcription polymerase chain reaction (RT-PCR) analysis was performed to track changes in transcript expression relevant to histogenesis and remodeling of the embryonic arterial wall. Our non-invasive extended OCT imaging technique for the microstructural data showed continuous vessel growth. OCT data coupled with the PIV technique revealed significant but intermitted increases in wall shear stress (WSS) between first and second assigned stages and a noticeable decrease afterwards. Growth rate, however, did not vary significantly throughout the embryonic period. Among all the genes studied, only the MMP-2 and CASP-3 expression levels remained unchanged during the time course. Concurrent relationships were obtained among the transcriptional modulation of the genes, vascular growth and hemodynamics-related changes. Further studies are indicated to determine cause and effect relationships and reversibility between mechanical and molecular regulation of vasculogenesis. PMID:27552150

  17. Ballistocardiogram as Proximal Timing Reference for Pulse Transit Time Measurement: Potential for Cuffless Blood Pressure Monitoring

    PubMed Central

    Kim, Chang-Sei; Carek, Andrew M.; Mukkamala, Ramakrishna; Inan, Omer T.; Hahn, Jin-Oh

    2015-01-01

    Goal We tested the hypothesis that the ballistocardiogram (BCG) waveform could yield a viable proximal timing reference for measuring pulse transit time (PTT). Methods From fifteen healthy volunteers, we measured PTT as the time interval between BCG and a non-invasively measured finger blood pressure (BP) waveform. To evaluate the efficacy of the BCG-based PTT in estimating BP, we likewise measured pulse arrival time (PAT) using the electrocardiogram (ECG) as proximal timing reference and compared their correlations to BP. Results BCG-based PTT was correlated with BP reasonably well: the mean correlation coefficient (r) was 0.62 for diastolic (DP), 0.65 for mean (MP) and 0.66 for systolic (SP) pressures when the intersecting tangent method was used as distal timing reference. Comparing four distal timing references (intersecting tangent, maximum second derivative, diastolic minimum and systolic maximum), PTT exhibited the best correlation with BP when the systolic maximum method was used (mean r value was 0.66 for DP, 0.67 for MP and 0.70 for SP). PTT was more strongly correlated with DP than PAT regardless of the distal timing reference: mean r value was 0.62 versus 0.51 (p=0.07) for intersecting tangent, 0.54 versus 0.49 (p=0.17) for maximum second derivative, 0.58 versus 0.52 (p=0.37) for diastolic minimum, and 0.66 versus 0.60 (p=0.10) for systolic maximum methods. The difference between PTT and PAT in estimating DP was significant (p=0.01) when the r values associated with all the distal timing references were compared altogether. However, PAT appeared to outperform PTT in estimating SP (p=0.31 when the r values associated with all the distal timing references were compared altogether). Conclusion We conclude that BCG is an adequate proximal timing reference in deriving PTT, and that BCG-based PTT may be superior to ECG-based PAT in estimating DP. Significance PTT with BCG as proximal timing reference has potential to enable convenient and ubiquitous cuffless

  18. The role of PDGF-B/TGF-β1/neprilysin network in regulating endothelial-to-mesenchymal transition in pulmonary artery remodeling.

    PubMed

    Song, Shasha; Zhang, Min; Yi, Zhi; Zhang, Hongyue; Shen, Tingting; Yu, Xiufeng; Zhang, Chen; Zheng, Xiaodong; Yu, Lei; Ma, Cui; Liu, Yang; Zhu, Daling

    2016-10-01

    Endothelial-to-mesenchymal transition (EndoMT) has been recognized as a major reason for the pulmonary artery remodeling (PAR) in pulmonary artery hypertension (PAH). However, the molecular mechanisms and regulatory pathways involved in the EndoMT remain undefined. In the present study, we have confirmed that EndoMT was occurred in pulmonary arteries of rats induced by hypoxia and monocrotaline and in hypoxic pulmonary artery endothelial cells (PAECs). Moreover, hypoxia increased the expression of platelet-derived growth factor (PDGF) and transforming growth factor-β1 (TGF-β1) and decreased the expression of neprilysin (NEP), which contributed to the hypoxia-induced EndoMT of PAECs. Furthermore, a reciprocal regulation of PDGF-B and TGF-β1 induced by decreasing NEP promoted the EndoMT of PAECs under hypoxia, which was a novel molecular mechanism to reveal the EndoMT participating in PAR. More importantly, imatinib, a PDGF receptor antagonist, relieved PAR and EndoMT in PAH rats. Thus, our results identify a novel mechanism to reveal the formation of EndoMT in PAH, and imply that imatinib may serve as a new therapeutic approach for treatment of the third cardiovascular disease. PMID:27373199

  19. Myocardial blood flow and its transit time, oxygen utilization, and efficiency of highly endurance-trained human heart.

    PubMed

    Heinonen, Ilkka; Kudomi, Nobuyuki; Kemppainen, Jukka; Kiviniemi, Antti; Noponen, Tommi; Luotolahti, Matti; Luoto, Pauliina; Oikonen, Vesa; Sipilä, Hannu T; Kopra, Jaakko; Mononen, Ilkka; Duncker, Dirk J; Knuuti, Juhani; Kalliokoski, Kari K

    2014-07-01

    Highly endurance-trained athlete's heart represents the most extreme form of cardiac adaptation to physical stress, but its circulatory alterations remain obscure. In the present study, myocardial blood flow (MBF), blood mean transit time (MTT), oxygen extraction fraction (OEF) and consumption (MVO2), and efficiency of cardiac work were quantified in highly trained male endurance athletes and control subjects at rest and during supine cycling exercise using [(15)O]-labeled radiotracers and positron emission tomography. Heart rate and MBF were lower in athletes both at rest and during exercise. OEF increased in response to exercise in both groups, but was higher in athletes (70 ± 21 vs. 63 ± 11 % at rest and 86 ± 13 vs. 73 ± 10 % during exercise). MTT was longer and vascular resistance higher in athletes both at rest and during exercise, but arterial content of 2,3-diphosphoglycerate (oxygen affinity) was unchanged. MVO2 per gram of myocardium trended (p = 0.08) lower in athletes both at rest and during exercise, while myocardial efficiency of work and MVO2 per beat were not different between groups. Arterial levels of free fatty acids were ~twofold higher in athletes likely leading to higher myocardial fatty acid oxidation and hence oxygen cost, which may have blunted the bradycardia-induced decrease in MVO2. Finally, the observed group differences in MBF, OEF, MTT and vascular resistance remained significant also after they were controlled for differences in MVO2. In conclusion, in highly endurance-trained human heart, increased myocardial blood transition time enables higher oxygen extraction levels with a lower myocardial blood flow and higher vascular resistance. These physiological adaptations to exercise training occur independently of the level of oxygen consumption and together with training-induced bradycardia may serve as mechanisms to increase functional reserve of the human heart. PMID:24866583

  20. Radial-femoral concordance in time and frequency domain-based estimates of systemic arterial respiratory variation.

    PubMed

    Thiele, Robert H; Colquhoun, Douglas A; Tucker-Schwartz, Jason M; Gillies, George T; Durieux, Marcel E

    2012-10-01

    Commonly used arterial respiratory variation metrics are based on mathematical analysis of arterial waveforms in the time domain. Because the shape of the arterial waveform is dependent on the site at which it is measured, we hypothesized that analysis of the arterial waveform in the frequency domain might provide a relatively site-independent means of measuring arterial respiratory variation. Radial and femoral arterial blood pressures were measured in nineteen patients undergoing liver transplantation. Systolic pressure variation (SPV), pulse pressure variation (PPV), area under the curve variation (AUCV), and mean arterial pressure variation (MAPV) at radial and femoral sites were calculated off-line. Two metrics, "Spectral Peak Ratio" (SPeR) and "Spectral Power Ratio" (SPoR) based on ratios of the spectral peak and spectral area (power) at the respiratory and cardiac frequencies, were calculated at both radial and femoral sites. Variance among radial-femoral differences was compared and correlation coefficients describing the relationship between respiratory variation at the radial and femoral sites were developed. The variance in radial-femoral differences were significantly different (p < 0.001). The correlation between radial and femoral estimates of respiratory variation were 0.746, 0.658, 0.858, 0.882, 0.941, and 0.925 for SPV, PPV, AUCV, MAPV, SPeR, and SPoR, respectively. Assuming a PPV treatment threshold of 12 % (or equivalent), differences in treatment decisions based on radial or femoral estimates would arise in 12, 14, 5.4, 5.7, 4.8, and 5.5 % of minutes for SPV, PPV, AUCV, MAPV, spectral peak ratio, and spectral power ratio, respectively. As compared to frequency domain-based estimates of respiratory variation, SPV and PPV are relatively dependent on the anatomic site at which they are measured. Spectral peak and power ratios are relatively site-independent means of measuring respiratory variation, and may offer a useful alternative to time

  1. No Timing Variations Observed in Third Transit of Snow-line Exoplanet Kepler-421b

    NASA Astrophysics Data System (ADS)

    Dalba, Paul A.; Muirhead, Philip S.

    2016-07-01

    We observed Kepler-421 during the anticipated third transit of the snow-line exoplanet Kepler-421b in order to constrain the existence and extent of transit timing variations (TTVs). Previously, the Kepler spacecraft only observed two transits of Kepler-421b, leaving the planet’s transit ephemeris unconstrained. Our visible light, time-series observations from the 4.3 m Discovery Channel Telescope were designed to capture pre-transit baseline and the partial transit of Kepler-421b, barring significant TTVs. We use the light curves to assess the probabilities of various transit models using both the posterior odds ratio and the Bayesian Information Criterion, and find that a transit model with no TTVs is favored to 3.6σ confidence. These observations suggest that Kepler-421b is either alone in its system or is only experiencing minor dynamic interactions with an unseen companion. With the Kepler-421b ephemeris constrained, we calculate future transit times and discuss the opportunity to characterize the atmosphere of this cold, long-period exoplanet via transmission spectroscopy. Our investigation emphasizes the difficulties associated with observing long-period exoplanet transits and the consequences that arise from failing to refine transit ephemerides.

  2. Regional Gastrointestinal Transit Times in Patients With Carcinoid Diarrhea: Assessment With the Novel 3D-Transit System

    PubMed Central

    Gregersen, Tine; Haase, Anne-Mette; Schlageter, Vincent; Gronbaek, Henning; Krogh, Klaus

    2015-01-01

    Background/Aims The paucity of knowledge regarding gastrointestinal motility in patients with neuroendocrine tumors and carcinoid diarrhea restricts targeted treatment. 3D-Transit is a novel, minimally invasive, ambulatory method for description of gastrointestinal motility. The system has not yet been evaluated in any group of patients. We aimed to test the performance of 3D-Transit in patients with carcinoid diarrhea and to compare the patients’ regional gastrointestinal transit times (GITT) and colonic motility patterns with those of healthy subjects. Methods Fifteen healthy volunteers and seven patients with neuroendocrine tumor and at least 3 bowel movements per day were investigated with 3D-Transit and standard radiopaque markers. Results Total GITT assessed with 3D-Transit and radiopaque markers were well correlated (Spearman’s rho = 0.64, P = 0.002). Median total GITT was 12.5 (range: 8.5–47.2) hours in patients versus 25.1 (range: 13.1–142.3) hours in healthy (P = 0.007). There was no difference in gastric emptying (P = 0.778). Median small intestinal transit time was 3.8 (range: 1.4–5.5) hours in patients versus 4.4 (range: 1.8–7.2) hours in healthy subjects (P = 0.044). Median colorectal transit time was 5.2 (range: 2.9–40.1) hours in patients versus 18.1 (range: 5.0–134.0) hours in healthy subjects (P = 0.012). Median frequency of pansegmental colonic movements was 0.45 (range: 0.03–1.02) per hour in patients and 0.07 (range: 0–0.61) per hour in healthy subjects (P = 0.045). Conclusions Three-dimensional Transit allows assessment of regional GITT in patients with diarrhea. Patients with carcinoid diarrhea have faster than normal gastrointestinal transit due to faster small intestinal and colorectal transit times. The latter is caused by an increased frequency of pansegmental colonic movements. PMID:26130638

  3. Community walking speed, sedentary or lying down time, and mortality in peripheral artery disease.

    PubMed

    McDermott, Mary M; Guralnik, Jack M; Ferrucci, Luigi; Tian, Lu; Kibbe, Melina R; Greenland, Philip; Green, David; Liu, Kiang; Zhao, Lihui; Wilkins, John T; Huffman, Mark D; Shah, Sanjiv J; Liao, Yihua; Gao, Ying; Lloyd-Jones, Donald M; Criqui, Michael H

    2016-04-01

    We studied whether slower community walking speed and whether greater time spent lying down or sleeping were associated with higher mortality in people with lower extremity peripheral artery disease (PAD). Participants with an ankle-brachial index (ABI) < 0.90 were identified from Chicago medical centers. At baseline, participants reported their usual walking speed outside their home and the number of hours they spent lying down or sleeping per day. Cause of death was adjudicated using death certificates and medical record review. Analyses were adjusted for age, sex, race, comorbidities, ABI, and other confounders. Of 1314 PAD participants, 189 (14.4%) died, including 63 cardiovascular disease (CVD) deaths. Mean follow-up was 34.9 months ± 18.1. Relative to average or normal pace (2-3 miles/hour), slower walking speed was associated with greater CVD mortality: no walking at all: hazard ratio (HR) = 4.17, 95% confidence interval (CI) = 1.46-11.89; casual strolling (0-2 miles/hour): HR = 2.24, 95% CI = 1.16-4.32; brisk or striding (>3 miles/hour): HR = 0.55, 95% CI = 0.07-4.30. These associations were not significant after additional adjustment for the six-minute walk. Relative to sleeping or lying down for 8-9 hours, fewer or greater hours sleeping or lying down were associated with higher CVD mortality: 4-7 hours: HR = 2.08, 95% CI = 1.06-4.05; 10-11 hours: HR = 4.07, 95% CI = 1.86-8.89; ⩾ 12 hours: HR = 3.75, 95% CI = 1.47-9.62. These associations were maintained after adjustment for the six-minute walk. In conclusion, slower walking speed outside the home and less than 8 hours or more than 9 hours lying down per day are potentially modifiable behaviors associated with increased CVD mortality in patients with PAD. PMID:26873873

  4. The physical origins of transit time measurements for rapid, single cell mechanotyping.

    PubMed

    Nyberg, Kendra D; Scott, Michael B; Bruce, Samuel L; Gopinath, Ajay B; Bikos, Dimitri; Mason, Thomas G; Kim, Jin Woong; Choi, Hong Sung; Rowat, Amy C

    2016-08-16

    The mechanical phenotype or 'mechanotype' of cells is emerging as a potential biomarker for cell types ranging from pluripotent stem cells to cancer cells. Using a microfluidic device, cell mechanotype can be rapidly analyzed by measuring the time required for cells to deform as they flow through constricted channels. While cells typically exhibit deformation timescales, or transit times, on the order of milliseconds to tens of seconds, transit times can span several orders of magnitude and vary from day to day within a population of single cells; this makes it challenging to characterize different cell samples based on transit time data. Here we investigate how variability in transit time measurements depends on both experimental factors and heterogeneity in physical properties across a population of single cells. We find that simultaneous transit events that occur across neighboring constrictions can alter transit time, but only significantly when more than 65% of channels in the parallel array are occluded. Variability in transit time measurements is also affected by the age of the device following plasma treatment, which could be attributed to changes in channel surface properties. We additionally investigate the role of variability in cell physical properties. Transit time depends on cell size; by binning transit time data for cells of similar diameters, we reduce measurement variability by 20%. To gain further insight into the effects of cell-to-cell differences in physical properties, we fabricate a panel of gel particles and oil droplets with tunable mechanical properties. We demonstrate that particles with homogeneous composition exhibit a marked reduction in transit time variability, suggesting that the width of transit time distributions reflects the degree of heterogeneity in subcellular structure and mechanical properties within a cell population. Our results also provide fundamental insight into the physical underpinnings of transit measurements

  5. Integral definition of transition time in the Landau-Zener model

    SciTech Connect

    Yan Yue; Wu Biao

    2010-02-15

    We give a general definition for the transition time in the Landau-Zener model. This definition allows us to compute numerically the Landau-Zener transition time at any sweeping rate without ambiguity in both diabatic and adiabatic bases. With this new definition, analytical results are obtained in both the adiabatic limit and the sudden limit.

  6. [Synchonization of the blood flow rate in arterial with the changing rate of space of blood pressure with time].

    PubMed

    Zhang, Shenghua; Qin, Renjia

    2012-10-01

    In physiology-related books, there are many relationship curves about blood flow rate in arteries and blood pressure changes with time, but there are not much explanation about such relationship. This is the very the question that the present article tries to answer. We clarified the relations between blood flow rate and blood pressure gradient using the experimental curves as the basis, using Poiseuille Law and relative knowledge of phisics and mathematics, and using analysis and reasoning. Based on the study, it can be concluded that in every course of cardiac cycle, the blood flow rate of any section in artery blood vessel is roughly synchronized with changing rate of space and time of the blood pressure, but blood flow rate is not synchronized with blood pressure. PMID:23198422

  7. Comparing Intra-Arterial Chemotherapy Combined With Intravesical Chemotherapy Versus Intravesical Chemotherapy Alone: A Randomised Prospective Pilot Study for T1G3 Bladder Transitional Cell Carcinoma After Bladder-Preserving Surgery

    SciTech Connect

    Chen, Junxing Yao, Zhijun Qiu, Shaopeng Chen, Lingwu; Wang, Yu Yang, Jianyong Li, Jiaping

    2013-12-15

    Purpose: To compare the efficacy of intra-arterial chemotherapy combined with intravesical chemotherapy versus intravesical chemotherapy alone for T1G3 bladder transitional cell carcinoma (BTCC) followed by bladder-preserving surgery. Materials and Methods: Sixty patients with T1G3 BTCC were randomly divided into two groups. After bladder-preserving surgery, 29 patients (age 30-80 years, 24 male and 5 female) received intra-arterial chemotherapy in combination with intravesical chemotherapy (group A), whereas 31 patients (age 29-83 years, 26 male and 5 female) were treated with intravesical chemotherapy alone (group B). Twenty-nine patients were treated with intra-arterial epirubicin (50 mg/m{sup 2}) + cisplatin (60 mg/m{sup 2}) chemotherapy 2-3 weeks after bladder-preserving surgery once every 4-6 weeks. All of the patients received the same intravesical chemotherapy: An immediate prophylactic was administered in the first 6 h. After that, therapy was administered one time per week for 8 weeks and then one time per month for 8 months. The instillation drug was epirubicin (50 mg/m{sup 2}) and lasted for 30-40 min each time. The end points were tumour recurrence (stage Ta, T1), tumour progression (to T2 or greater), and disease-specific survival. During median follow-up of 22 months, the overall survival rate, tumour-specific death rate, recurrence rate, progression rate, time to first recurrence, and adverse reactions were compared between groups. Results: The recurrence rates were 10.3 % (3 of 29) in group A and 45.2 % (14 of 31) in group B, and the progression rates were 0 % (0 of 29) in group A and 22.6 % (7 of 31) in group B. There was a significant difference between the two groups regarding recurrence (p = 0.004) and progression rates (p = 0.011). Median times to first recurrence in the two groups were 15 and 6.5 months, respectively. The overall survival rates were 96.6 and 87.1 %, and the tumour-specific death rates were 0 % (0 of 29) and 13.5 % (4 of 31

  8. The use of Doppler evaluation of the canine umbilical artery in prediction of delivery time and fetal distress.

    PubMed

    Giannico, Amália Turner; Gil, Elaine Mayumi Ueno; Garcia, Daniela Aparecida Ayres; Froes, Tilde Rodrigues

    2015-03-01

    The aim of this study was to describe changes in umbilical artery blood flow in the later stages of canine pregnancy. Seventeen pregnant bitches were examined sonographically to evaluate umbilical artery blood flow at the following antepartum times: 120-96, 96-72, 72-48, 48-24, 24-12, 12-6 and 6-1h. The peak systolic velocity and end diastolic velocity were measured to calculate the resistive index (RI). Bitches were classified into two groups according to delivery method: normal delivery (Group 1, n=11) and Cesarean section, due to fetal distress, (Group 2, n=6). During the study, the RI of the umbilical artery in bitches in Group 1 significantly declined in the time periods 72-48, 24-12, 12-6 and 6-1h before delivery when compared to the reference RI (120-96h antepartum period), with values ​​below 0.7 in the 12-6 and 6-1h periods. In Group 2, the RI decreased significantly in the antepartum periods 96-72, 72-48, 48-24h with respect to the period 120-96h, and increased in the periods from 24-12, 12-6 and 6-1h (being significantly higher in this last period) until the time of Cesarean section. Therefore monitoring of changes in umbilical artery RI in the pre-partum period may provide information about time of delivery in bitches and also assist in the diagnosis of possible dystocia and fetal distress. PMID:25596637

  9. Numerical assessment of time-domain methods for the estimation of local arterial pulse wave speed.

    PubMed

    Alastruey, Jordi

    2011-03-15

    A local estimation of pulse wave speed c, an important predictor of cardiovascular events, can be obtained at arterial locations where simultaneous measurements of blood pressure (P) and velocity (U), arterial diameter (D) and U, flow rate (Q) and cross-sectional area (A), or P and D are available, using the PU-loop, sum-of-squares (∑(2)), lnDU-loop, QA-loop or new D(2)P-loop methods. Here, these methods were applied to estimate c from numerically generated P, U, D, Q and A waveforms using a visco-elastic one-dimensional model of the 55 larger human systemic arteries in normal conditions. Theoretical c were calculated from the parameters of the model. Estimates of c given by the loop methods were closer to theoretical values and more uniform within each arterial segment than those obtained using the ∑(2). The smaller differences between estimates and theoretical values were obtained using the D(2)P-loop method, with root-mean-square errors (RMSE) smaller than 0.18 ms(-1), followed by averaging the two c given by the PU- and lnDU-loops (RMSE <2.99 ms(-1)). In general, the errors of the PU-, lnDU- and QA-loops decreased at locations where visco-elastic effects were small and nearby junctions were well-matched for forward-travelling waves. The ∑(2) performed better at proximal locations. PMID:21211799

  10. Impact of the augmentation time ratio on direct measurement of central aortic pressure in the presence of coronary artery disease.

    PubMed

    Mizuno, Atsushi; Miyauchi, Katsumi; Nishizaki, Yuji; Yamazoe, Masahiro; Komatsu, Ikki; Asano, Taku; Mitsuhashi, Hirotsugu; Nishi, Yutaro; Niwa, Koichiro; Daida, Hiroyuki

    2015-10-01

    The augmentation index measured by using the central artery pressure is associated with an increased risk of coronary artery disease (CAD). However, no study has examined the role of the time duration of the central artery pressure on CAD. Therefore, we evaluated the relationship between the central blood pressure time duration and the presence of CAD. All patients without a history of revascularization or prior myocardial infarction who underwent an elective coronary angiography at one of the two hospitals from January to September 2013 were analyzed. CAD was defined as a significant stenosis in one of the main coronary branches. The augmentation time ratio was defined as the ratio of the reflection to peak systolic time T2T1 duration divided by the peak systolic time to aortic notch T3T2 duration. We analyzed the relationship between the central pressure waveform (not only augmentation pressure) and the presence of CAD. A total of 146 (57.3%) out of 255 patients had a significant CAD. T2T1 duration was longer in the CAD group than the no CAD group, and the T3T2 duration was shorter in the CAD group than the no CAD group. The augmentation time ratio (T2T1/T3T2) was significantly larger in the CAD group than in the no CAD group. The augmentation index and augmentation pressure were lower in the no CAD group, but this difference was not statistically significant. The augmentation time ratio was an independent factor related to no CAD, especially in patients with a high augmentation index (odds ratio, 2.17; 95% confidence interval, 1.02-4.63). The augmentation time ratio was an independent factor related to the presence of CAD. PMID:25854988

  11. Investigation of Timing to Switch Control Mode in Powered Knee Prostheses during Task Transitions

    PubMed Central

    Zhang, Fan; Liu, Ming; Huang, He

    2015-01-01

    Current powered prosthetic legs require switching control modes according to the task the user is performing (e.g. level-ground walking, stair climbing, walking on slopes, etc.). To allow prosthesis users safely and seamlessly transition between tasks, it is critical to determine when to switch the prosthesis control mode during task transitions. Our previous study defined critical timings for different types of task transitions in ambulation; however, it is unknown whether it is the unique timing that allows safe and seamless transitions. The goals of this study were to (1) systematically investigate the effects of mode switch timing on the prosthesis user’s performance in task transitions, and (2) identify appropriate timing to switch the prosthesis control mode so that the users can seamlessly transition between different locomotion tasks. Five able-bodied (AB) and two transfemoral (TF) amputee subjects were tested as they wore a powered knee prosthesis. The prosthesis control mode was switched manually at various times while the subjects performed different types of task transitions. The subjects’ task transition performances were evaluated by their walking balance and success in performing seamless task transitions. The results demonstrated that there existed a time window within which switching the prosthesis control mode neither interrupted the subjects’ task transitions nor disturbed their walking balance. Therefore, the results suggested the control mode switching of a lower limb prosthesis can be triggered within an appropriate time window instead of a specific timing or an individual phase. In addition, a generalized criterion to determine the appropriate mode switch timing was proposed. The outcomes of this study could provide important guidance for future designs of neurally controlled powered knee prostheses that are safe and reliable to use. PMID:26197084

  12. Time Resolved Phase Transitions via Dynamic Transmission Electron Microscopy

    SciTech Connect

    Reed, B W; Armstrong, M R; Blobaum, K J; Browning, N D; Burnham, A K; Campbell, G H; Gee, R; Kim, J S; King, W E; Maiti, A; Piggott, W T; Torralva, B R

    2007-02-22

    The Dynamic Transmission Electron Microscope (DTEM) project is developing an in situ electron microscope with nanometer- and nanosecond-scale resolution for the study of rapid laser-driven processes in materials. We report on the results obtained in a year-long LDRD-supported effort to develop DTEM techniques and results for phase transitions in molecular crystals, reactive multilayer foils, and melting and resolidification of bismuth. We report the first in situ TEM observation of the HMX {beta}-{delta} phase transformation in sub-{micro}m crystals, computational results suggesting the importance of voids and free surfaces in the HMX transformation kinetics, and the first electron diffraction patterns of intermediate states in fast multilayer foil reactions. This project developed techniques which are applicable to many materials systems and will continue to be employed within the larger DTEM effort.

  13. Frequency of close companions among Kepler planets—a transit time variation study

    SciTech Connect

    Xie, Ji-Wei; Wu, Yanqin; Lithwick, Yoram E-mail: wu@astro.utoronto.ca

    2014-07-10

    A transiting planet exhibits sinusoidal transit time variations (TTVs) if perturbed by a companion near a mean-motion resonance. We search for sinusoidal TTVs in more than 2600 Kepler candidates, using the publicly available Kepler light curves (Q0-Q12). We find that the TTV fractions rise strikingly with the transit multiplicity. Systems where four or more planets transit enjoy a TTV fraction that is roughly five times higher than those where a single planet transits, and about twice as high as those for doubles and triples. In contrast, models in which all transiting planets arise from similar dynamical configurations predict comparable TTV fractions among these different systems. One simple explanation for our results is that there are at least two different classes of Kepler systems, one closely packed and one more sparsely populated.

  14. The use of transit timing to detect terrestrial-mass extrasolar planets.

    PubMed

    Holman, Matthew J; Murray, Norman W

    2005-02-25

    Future surveys for transiting extrasolar planets are expected to detect hundreds of jovian-mass planets and tens of terrestrial-mass planets. For many of these newly discovered planets, the intervals between successive transits will be measured with an accuracy of 0.1 to 100 minutes. We show that these timing measurements will allow for the detection of additional planets in the system (not necessarily transiting) by their gravitational interaction with the transiting planet. The transit-time variations depend on the mass of the additional planet, and in some cases terrestrial-mass planets will produce a measurable effect. In systems where two planets are seen to transit, the density of both planets can be determined without radial-velocity observations. PMID:15731449

  15. SOPHIE velocimetry of Kepler transit candidates. X. KOI-142 c: first radial velocity confirmation of a non-transiting exoplanet discovered by transit timing

    NASA Astrophysics Data System (ADS)

    Barros, S. C. C.; Díaz, R. F.; Santerne, A.; Bruno, G.; Deleuil, M.; Almenara, J.-M.; Bonomo, A. S.; Bouchy, F.; Damiani, C.; Hébrard, G.; Montagnier, G.; Moutou, C.

    2014-01-01

    The exoplanet KOI-142b (Kepler-88b) shows transit timing variations (TTVs) with a semi-amplitude of ~12 h, which earned it the nickname "king of transit variations". Only the transit of planet b was detected in the Kepler data with an orbital period of ~10.92 days and a radius of ~0.36 RJup. The TTVs together with the transit duration variations of KOI-142b were analysed recently, finding a unique solution for a companion-perturbing planet. An outer non-transiting companion was predicted, KOI-142c, with a mass of 0.626 ± 0.03 MJup and a period of 22.3397-0.0018+0.0021 days, which is close to the 2:1 mean-motion resonance with the inner transiting planet. We report an independent confirmation of KOI-142c using radial velocity observations with the SOPHIE spectrograph at the Observatoire de Haute-Provence. We derive an orbital period of 22.10 ± 0.25 days and a minimum planetary mass of 0.760.16+0.32 MJup, both in good agreement with the predictions by previous transit timing analysis. Therefore, this is the first radial velocity confirmation of a non-transiting planet discovered with TTVs, providing an independent validation of the TTVs technique. Based on observations collected with the NASA Kepler satellite and with the SOPHIE spectrograph on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France.Tables 2 and 3 are available in electronic form at http://www.aanda.org

  16. Alterations of calf venous and arterial compliance following acclimation to heat administered at a fixed daily time in humans

    NASA Astrophysics Data System (ADS)

    Maruyama, Megumi; Hara, Toshiko; Hashimoto, Michio; Koga, Miki; Shido, Osamu

    2006-05-01

    We investigated the effects of heat acclimation on venous and arterial compliance in humans. Four male and four female volunteers were exposed to an ambient temperature of 40°C and relative humidity of 40% for 4 h (1330 1730 hours) per day for 9 10 consecutive days. The calf venous compliance (CV) was estimated using venous occlusion plethysmography with a mercury-in-silastic strain gauge placed around the right calf at its maximum girth. The compliance of the small (CSA) and large (CLA) arteries were assessed by reflective and capacitance compliance by analyzing the radial artery blood pressure waveforms, basing on the use of a modified Windkessel model. The calf CV, CSA, CLA, systolic and diastolic blood pressures, heart rate and core temperature were determined twice a day, 0930 1100 hours (AM test) and 1500 1630 hours (PM test), in both heat-acclimated and non-heat-acclimated (control) conditions. Heat acclimation appeared to decrease blood pressures, heart rate and significantly lowered core temperature only in the PM test. In the control condition, the calf CV was not affected by the time of day and the CSA was significantly depressed in the PM test. After acclimation to heat, the calf CV significantly increased and the CSA did not decrease in the PM test. The results presented suggest that repeated heat exposure in humans, for 4 h at a fixed time daily, increases the calf CV and the CSA particularly during the period when the subjects were previously exposed to heat.

  17. [Effect of preserving left colic artery during radical operation of rectal cancer on anastomotic leakage and operation time].

    PubMed

    Zang, Lu; Ma, Junjun; Zheng, Minhua

    2016-04-01

    Surgical treatment for rectal cancer has changed radically in recent years since the introduction of the principle of total mesorectal excision (TME) and technique of laparoscopic approach. The emphasis of management for vessels in laparoscopic TME surgery for rectal cancer is mainly focused on the inferior mesenteric artery (IMA) and its branches. Two alternatives of the level to execute the IMA are high ligation(without preservation of left colic artery, LCA) and low ligation (with preservation of LCA). In this article, we review the latest literature from China and foreign countries concerning this issue, and combine with our own experience to investigate the effect of LCA preserving on anastomotic leakage and operation time, which may provide a reference for proper choice of the management of IMA in rectal cancer surgery. PMID:27112468

  18. Effects of unsteadiness and non-Newtonian rheology on blood flow through a tapered time-variant stenotic artery

    NASA Astrophysics Data System (ADS)

    Zaman, A.; Ali, N.; Sajid, M.; Hayat, T.

    2015-03-01

    A two-dimensional model is used to analyze the unsteady pulsatile flow of blood through a tapered artery with stenosis. The rheology of the flowing blood is captured by the constitutive equation of Carreau model. The geometry of the time-variant stenosis has been used to carry out the present analysis. The flow equations are set up under the assumption that the lumen radius is sufficiently smaller than the wavelength of the pulsatile pressure wave. A radial coordinate transformation is employed to immobilize the effect of the vessel wall. The resulting partial differential equations along with the boundary and initial conditions are solved using finite difference method. The dimensionless radial and axial velocity, volumetric flow rate, resistance impedance and wall shear stress are analyzed for normal and diseased artery with particular focus on variation of these quantities with non-Newtonian parameters.

  19. Transitions.

    ERIC Educational Resources Information Center

    Nathanson, Jeanne H., Ed.

    1993-01-01

    This theme issue on transitions for individuals with disabilities contains nine papers discussing transition programs and issues. "Transition Issues for the 1990s," by Michael J. Ward and William D. Halloran, discusses self-determination, school responsibility for transition, continued educational engagement of at-risk students, and service…

  20. The role of hillslopes in stream flow response: connectivity, flow path, and transit time

    NASA Astrophysics Data System (ADS)

    McGuire, K. J.; McDonnell, J. J.

    2006-12-01

    Subsurface flow from hillslopes is widely recognized as an important contributor to stream flow generation; however, processes that control how and when hillslopes connect to streams remain unclear. Much of the difficulty in deciphering hillslope response in the stream is due to riparian zone modulation of these inputs. We investigated stream and hillslope runoff dynamics in a 10 ha catchment in the western Cascades of Oregon where the riparian zone has been removed by debris flows, providing an unambiguous hillslope hydrologic signal to the stream channel. Water transit time was used as a framework to develop a conceptual stream flow generation model for the small basin. We based our conceptualization on observations of hydrometric, stable isotope, and applied tracer responses and computed transit times for multiple runoff components using a simple linear systems model. Event water mean transit times (8 to 34 h) and rapid breakthrough from applied hillslope tracer additions, demonstrated that contributing areas extend far upslope during events. Despite rapid hillslope transport processes during events, vadose zone water and runoff mean transit times during non-storm conditions were greater than the timescale of storm events. Vadose zone water mean transit times ranged between 10 and 25 days. Hillslope seepage and catchment baseflow mean transit times were between 1 and 2 years. We describe a conceptual model that captures variable physical flow pathways and transit times through changing antecedent wetness conditions that illustrate the different stages of hillslope and stream connectivity.

  1. Solid volume fraction estimation of bone:marrow replica models using ultrasound transit time spectroscopy.

    PubMed

    Wille, Marie-Luise; Langton, Christian M

    2016-02-01

    The acceptance of broadband ultrasound attenuation (BUA) for the assessment of osteoporosis suffers from a limited understanding of both ultrasound wave propagation through cancellous bone and its exact dependence upon the material and structural properties. It has recently been proposed that ultrasound wave propagation in cancellous bone may be described by a concept of parallel sonic rays; the transit time of each ray defined by the proportion of bone and marrow propagated. A Transit Time Spectrum (TTS) describes the proportion of sonic rays having a particular transit time, effectively describing the lateral inhomogeneity of transit times over the surface aperture of the receive ultrasound transducer. The aim of this study was to test the hypothesis that the solid volume fraction (SVF) of simplified bone:marrow replica models may be reliably estimated from the corresponding ultrasound transit time spectrum. Transit time spectra were derived via digital deconvolution of the experimentally measured input and output ultrasonic signals, and compared to predicted TTS based on the parallel sonic ray concept, demonstrating agreement in both position and amplitude of spectral peaks. Solid volume fraction was calculated from the TTS; agreement between true (geometric calculation) with predicted (computer simulation) and experimentally-derived values were R(2)=99.9% and R(2)=97.3% respectively. It is therefore envisaged that ultrasound transit time spectroscopy (UTTS) offers the potential to reliably estimate bone mineral density and hence the established T-score parameter for clinical osteoporosis assessment. PMID:26455950

  2. In vivo validation of a transit-time ultrasonic volume flow meter.

    PubMed

    Hartman, J C; Olszanski, D A; Hullinger, T G; Brunden, M N

    1994-06-01

    The objective of this investigation was to validate a transit-time ultrasound blood flow metering system in vivo. Implanted chronically and acutely on the ascending aorta of the dog, the transit-time flow probe determined varying flow rates simultaneously with measurements made by the electromagnetic flow metering method. The transit-time technique was also compared to two methods in which blood was collected volumetrically by either graduated cylinder (ascending aorta/dog) or pump withdrawal (abdominal aorta/cat). Statistical analysis of the results provided evidence that the transit-time ultrasound method measured in vivo blood flow rate no differently than the electromagnetic or pump withdrawal techniques, however, transit-time determinations of blood volume were 10% below that indicated by graduated cylinder collection. With transit time represented on the y-axis, three linear regressions of all paired blood flow measurements were calculated yielding the following slopes (delta y/delta x) and regression coefficients (r), respectively: electromagnetic (1.00, 0.98), graduated cylinder (0.85, 0.93), and pump withdrawal (0.93, 1.00). The results validate the transit-time ultrasound system used in the present investigation as an accurate method capable of measuring blood flow in both acutely and chronically instrumented animal preparations. PMID:8068977

  3. The acceleration of energetic particles in the interplanetary medium by transit-time damping

    NASA Technical Reports Server (NTRS)

    Fisk, L. A.

    1976-01-01

    Transit time damping is examined as a possible means for accelerating low energy particles in co-rotating streams and interstellar ions. Data show that: the protons in co-rotating streams may be accelerated by transient-time damping the small-scale variations in the field magnitude that are observed at a low level in the inner solar system. The interstellar ions may be accelerated by transit time damping large-scale field variations in the outer solar system.

  4. Critical capacity, travel time delays and travel time distribution of rapid mass transit systems

    NASA Astrophysics Data System (ADS)

    Legara, Erika Fille; Monterola, Christopher; Lee, Kee Khoon; Hung, Gih Guang

    2014-07-01

    We set up a mechanistic agent-based model of a rapid mass transit system. Using empirical data from Singapore’s unidentifiable smart fare card, we validate our model by reconstructing actual travel demand and duration of travel statistics. We subsequently use this model to investigate two phenomena that are known to significantly affect the dynamics within the RTS: (1) overloading in trains and (2) overcrowding in the RTS platform. We demonstrate that by varying the loading capacity of trains, a tipping point emerges at which an exponential increase in the duration of travel time delays is observed. We also probe the impact on the rail system dynamics of three types of passenger growth distribution across stations: (i) Dirac delta, (ii) uniform and (iii) geometric, which is reminiscent of the effect of land use on transport. Under the assumption of a fixed loading capacity, we demonstrate the dependence of a given origin-destination (OD) pair on the flow volume of commuters in station platforms.

  5. First-time viewers' comprehension of films: bridging shot transitions.

    PubMed

    Ildirar, Sermin; Schwan, Stephan

    2015-02-01

    Which perceptual and cognitive prerequisites must be met in order to be able to comprehend a film is still unresolved and a controversial issue. In order to gain some insights into this issue, our field experiment investigates how first-time adult viewers extract and integrate meaningful information across film cuts. Three major types of commonalities between adjacent shots were differentiated, which may help first-time viewers with bridging the shots: pictorial, causal, and conceptual. Twenty first-time, 20 low-experienced and 20 high-experienced viewers from Turkey were shown a set of short film clips containing these three kinds of commonalities. Film clips conformed also to the principles of continuity editing. Analyses of viewers' spontaneous interpretations show that first-time viewers indeed are able to notice basic pictorial (object identity), causal (chains of activity), as well as conceptual (links between gaze direction and object attention) commonalities between shots due to their close relationship with everyday perception and cognition. However, first-time viewers' comprehension of the commonalities is to a large degree fragile, indicating the lack of a basic notion of what constitutes a film. PMID:24654735

  6. The use of content and timing to predict turn transitions

    PubMed Central

    Garrod, Simon; Pickering, Martin J.

    2015-01-01

    For addressees to respond in a timely fashion, they cannot simply process the speaker's utterance as it occurs and wait till it finishes. Instead, they predict both when the speaker will conclude and what linguistic forms will be used. While doing this, they must also prepare their own response. To explain this, we draw on the account proposed by Pickering and Garrod (2013a), in which addressees covertly imitate the speaker's utterance and use this to determine the intention that underlies their upcoming utterance. They use this intention to predict when and how the utterance will end, and also to drive their own production mechanisms for preparing their response. Following Arnal and Giraud (2012), we distinguish between mechanisms that predict timing and content. In particular, we propose that the timing mechanism relies on entrainment of low-frequency oscillations between speech envelope and brain. This constrains the context that feeds into the determination of the speaker's intention and hence the timing and form of the upcoming utterance. This approach typically leads to well-timed contributions, but also provides a mechanism for resolving conflicts, for example when there is unintended speaker overlap. PMID:26124728

  7. First Semester Experiences of Professionals Transitioning to Full-Time Doctoral Study

    ERIC Educational Resources Information Center

    Austin, Janice; Cameron, Tracey; Glass, Martha; Kosko, Karl; Marsh, Fulya; Abdelmagid, Randa; Burge, Penny

    2009-01-01

    The purpose of this phenomenological study was to examine the experiences of full-time doctoral students transitioning from professional employment. Interview data were interpreted through a student transition and socialization conceptual framework. Five themes emerged: identity, integration, support systems, perseverance, and success vs.…

  8. A multivariate time-frequency method to characterize the influence of respiration over heart period and arterial pressure

    NASA Astrophysics Data System (ADS)

    Orini, Michele; Bailón, Raquel; Laguna, Pablo; Mainardi, Luca T.; Barbieri, Riccardo

    2012-12-01

    Respiratory activity introduces oscillations both in arterial pressure and heart period, through mechanical and autonomic mechanisms. Respiration, arterial pressure, and heart period are, generally, non-stationary processes and the interactions between them are dynamic. In this study we present a methodology to robustly estimate the time course of cross spectral indices to characterize dynamic interactions between respiratory oscillations of heart period and blood pressure, as well as their interactions with respiratory activity. Time-frequency distributions belonging to Cohen's class are used to estimate time-frequency (TF) representations of coherence, partial coherence and phase difference. The characterization is based on the estimation of the time course of cross spectral indices estimated in specific TF regions around the respiratory frequency. We used this methodology to describe the interactions between respiration, heart period variability (HPV) and systolic arterial pressure variability (SAPV) during tilt table test with both spontaneous and controlled respiratory patterns. The effect of selective autonomic blockade was also studied. Results suggest the presence of common underling mechanisms of regulation between cardiovascular signals, whose interactions are time-varying. SAPV changes followed respiratory flow both in supine and standing positions and even after selective autonomic blockade. During head-up tilt, phase differences between respiration and SAPV increased. Phase differences between respiration and HPV were comparable to those between respiration and SAPV during supine position, and significantly increased during standing. As a result, respiratory oscillations in SAPV preceded respiratory oscillations in HPV during standing. Partial coherence was the most sensitive index to orthostatic stress. Phase difference estimates were consistent among spontaneous and controlled breathing patterns, whereas coherence was higher in spontaneous breathing

  9. Time-delay-induced phase-transition to synchrony in coupled bursting neurons

    NASA Astrophysics Data System (ADS)

    Adhikari, Bhim Mani; Prasad, Awadhesh; Dhamala, Mukeshwar

    2011-06-01

    Signal transmission time delays in a network of nonlinear oscillators are known to be responsible for a variety of interesting dynamic behaviors including phase-flip transitions leading to synchrony or out of synchrony. Here, we uncover that phase-flip transitions are general phenomena and can occur in a network of coupled bursting neurons with a variety of coupling types. The transitions are marked by nonlinear changes in both temporal and phase-space characteristics of the coupled system. We demonstrate these phase-transitions with Hindmarsh-Rose and Leech-Heart interneuron models and discuss the implications of these results in understanding collective dynamics of bursting neurons in the brain.

  10. Management of Type 9 Hepatic Arterial Anatomy at the time of Pancreaticoduodenectomy: Considerations for Preservation and Reconstruction of a Completely Replaced Common Hepatic Artery.

    PubMed

    Hicks, Caitlin W; Burkhart, Richard A; Weiss, Matthew J; Wolfgang, Christopher L; Cameron, Andrew M; Pawlik, Timothy M

    2016-07-01

    Recognition and management of aberrant hepatic arterial anatomy for patients undergoing pancreaticoduodenectomy (PD) are critical to ensure safe completion of the operation. When the common hepatic artery (CHA) is noted to emanate from the superior mesenteric artery (Michels' type 9 variant), it is vulnerable to injury during the dissection required for PD. While this anatomy does not preclude an operation, care must be taken to avoid injury, often by identifying the CHA throughout its entire course before beginning the dissection of the portal venous structures. The oncologic principle that cautions against resection of a pancreatic cancer when it involves the CHA in its standard position may not universally apply to tumors that focally involve the CHA in the type 9 anatomic variant. In highly selected patients, surgical resection may be entertained as disease biology may be analogous to local involvement of the gastroduodenal artery in a patient with standard anatomy. Here, we review the indications, techniques, and outcomes associated with arterial resection and reconstruction during pancreatectomy among patients with a pancreatic tumor involving a common hepatic artery arising from the superior mesenteric artery. PMID:27138326

  11. TTVFast: An efficient and accurate code for transit timing inversion problems

    SciTech Connect

    Deck, Katherine M.; Agol, Eric; Holman, Matthew J.; Nesvorný, David

    2014-06-01

    Transit timing variations (TTVs) have proven to be a powerful technique for confirming Kepler planet candidates, for detecting non-transiting planets, and for constraining the masses and orbital elements of multi-planet systems. These TTV applications often require the numerical integration of orbits for computation of transit times (as well as impact parameters and durations); frequently tens of millions to billions of simulations are required when running statistical analyses of the planetary system properties. We have created a fast code for transit timing computation, TTVFast, which uses a symplectic integrator with a Keplerian interpolator for the calculation of transit times. The speed comes at the expense of accuracy in the calculated times, but the accuracy lost is largely unnecessary, as transit times do not need to be calculated to accuracies significantly smaller than the measurement uncertainties on the times. The time step can be tuned to give sufficient precision for any particular system. We find a speed-up of at least an order of magnitude relative to dynamical integrations with high precision using a Bulirsch-Stoer integrator.

  12. Effect of work intensity on time delay in mediation of ventilation by arterial carbon dioxide during recovery from impulse exercise.

    PubMed

    Afroundeh, R; Arimitsu, T; Yamanaka, R; Lian, C S; Shirakawa, K; Yunoki, T; Yano, T

    2014-01-01

    Time delay in the mediation of ventilation (V(.)E) by arterial CO(2) pressure (PaCO(2)) was studied during recovery from short impulse-like exercises with different work loads of recovery. Subjects performed two tests including 10-s impulse like exercise with work load of 200 watts and 15-min recovery with 25 watts in test one and 50 watts in test two. V(.)E, end tidal CO(2) pressure (PETCO(2)) and heart rate (HR) were measured continuously during rest, warming up, exercise and recovery. PaCO(2) was estimated from PETCO(2) and tidal volume (V(T)). Results showed that predicted arterial CO(2) pressure (PaCO(2 pre)) increased during recovery in both tests. In both tests, V(.)E increased and peaked at the end of exercise. V(.)E decreased in the first few seconds of recovery but started to increase again. The highest correlation coefficient between PaCO(2 pre) and V(.)E was obtained in the time delay of 7 s (r=0.854) in test one and in time delays of 6 s (r=0.451) and 31 s (r=0.567) in test two. HR was significantly higher in test two than in test one. These results indicate that PaCO(2 pre) drives V(.)E with a time delay and that higher work intensity induces a shorter time delay. PMID:24702492

  13. Studies in Transition and Time Varying Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Grosch, Chester E.

    2004-01-01

    The research focused on two areas: (a) the dynamics of forced turbulent flows and (b) time filtered Large Eddy Simulations (TLES). The dynamics of turbulent flows arising from external forcing of the turbulence are poorly understood. In particular, here are many unanswered questions relating the basic dynamical balances and the existence or nonexistence of statistical equilibrium of forced turbulent flows. The research used direct numerical simulations to explore these questions. The properties of the temporally filtered Navier-Stokes equations were also studied.

  14. Methods for detecting early warnings of critical transitions in time series illustrated using simulated ecological data.

    PubMed

    Dakos, Vasilis; Carpenter, Stephen R; Brock, William A; Ellison, Aaron M; Guttal, Vishwesha; Ives, Anthony R; Kéfi, Sonia; Livina, Valerie; Seekell, David A; van Nes, Egbert H; Scheffer, Marten

    2012-01-01

    Many dynamical systems, including lakes, organisms, ocean circulation patterns, or financial markets, are now thought to have tipping points where critical transitions to a contrasting state can happen. Because critical transitions can occur unexpectedly and are difficult to manage, there is a need for methods that can be used to identify when a critical transition is approaching. Recent theory shows that we can identify the proximity of a system to a critical transition using a variety of so-called 'early warning signals', and successful empirical examples suggest a potential for practical applicability. However, while the range of proposed methods for predicting critical transitions is rapidly expanding, opinions on their practical use differ widely, and there is no comparative study that tests the limitations of the different methods to identify approaching critical transitions using time-series data. Here, we summarize a range of currently available early warning methods and apply them to two simulated time series that are typical of systems undergoing a critical transition. In addition to a methodological guide, our work offers a practical toolbox that may be used in a wide range of fields to help detect early warning signals of critical transitions in time series data. PMID:22815897

  15. Methods for Detecting Early Warnings of Critical Transitions in Time Series Illustrated Using Simulated Ecological Data

    PubMed Central

    Dakos, Vasilis; Carpenter, Stephen R.; Brock, William A.; Ellison, Aaron M.; Guttal, Vishwesha; Ives, Anthony R.; Kéfi, Sonia; Livina, Valerie; Seekell, David A.; van Nes, Egbert H.; Scheffer, Marten

    2012-01-01

    Many dynamical systems, including lakes, organisms, ocean circulation patterns, or financial markets, are now thought to have tipping points where critical transitions to a contrasting state can happen. Because critical transitions can occur unexpectedly and are difficult to manage, there is a need for methods that can be used to identify when a critical transition is approaching. Recent theory shows that we can identify the proximity of a system to a critical transition using a variety of so-called ‘early warning signals’, and successful empirical examples suggest a potential for practical applicability. However, while the range of proposed methods for predicting critical transitions is rapidly expanding, opinions on their practical use differ widely, and there is no comparative study that tests the limitations of the different methods to identify approaching critical transitions using time-series data. Here, we summarize a range of currently available early warning methods and apply them to two simulated time series that are typical of systems undergoing a critical transition. In addition to a methodological guide, our work offers a practical toolbox that may be used in a wide range of fields to help detect early warning signals of critical transitions in time series data. PMID:22815897

  16. Transitions.

    ERIC Educational Resources Information Center

    Field, David; And Others

    1992-01-01

    Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)

  17. Effect of coupling parasitics and CMOS driver width on transition time for dynamic inputs

    NASA Astrophysics Data System (ADS)

    Sharma, Devendra Kumar; Kaushik, Brajesh Kumar; Sharma, R. K.

    2014-05-01

    This article analyses the effect of coupling parasitics and CMOS gate driver width on transition time delay of coupled interconnects driven by dynamically switching inputs. Propagation delay through an interconnect is dependent not only on the technology/topology but also on many other factors such as input transition time, load characteristic, driving gate dimensions and so on. The delay is affected by rise/fall time of the signal, which in turn is dependent on the driving gate and the load presented to it. The signal transition time is also a strong function of wire parasitics. This article addresses the different issues of signal transition time. The impact of inter-wire parasitics and driver width on signal transition time are presented in this article. Furthermore, the effect of unequal transition time of the inputs to interconnect lines on crosstalk noise and delay is analysed. To demonstrate these effects, two distributed RLC lines coupled capacitively and inductively are taken into consideration. The simulations are run at three different technology nodes, viz. 65 nm, 90 nm and 130 nm.

  18. Phase Transition in strongly-correlated VO2: Time-domainAssignment of Cause and Effect

    SciTech Connect

    Cavalleri, A.; Dekorsy, Th.; Chong, H.H.; Kieffer, J.C.; Schoenlein, R.W.

    2004-07-22

    We establish time-domain hierarchy between structural andelectronic effects in the strongly correlated system VO2. Theinsulator-to-metal transition is driven directly by structural changerather than by electron-electron correlations.

  19. Effect of changing transit time on colonic microbial metabolism in man.

    PubMed Central

    Stephen, A M; Wiggins, H S; Cummings, J H

    1987-01-01

    An investigation was made of the effect of changing mean transit time (MTT) by administration of drugs which affect colonic motility on faecal microbial mass in man. Senokot was used to accelerate and codeine and/or loperamide to prolong transit in subjects maintained on a constant high fibre diet. Doses of Senokot or codeine/loperamide were adjusted to halve or double transit time measured during a three week control period on diet alone. Stools were collected throughout and analysed for bacterial mass by a gravimetric procedure. Transit was measured by a continuous marker method. Senokot decreased mean transit time from 63.9 to 25.0 hours (n = 6), with increased stool weight from 148 to 285 g/day. Bacterial mass increased in all subjects from a mean of 16.5 to 20.3 g/day (dry weight) (p less than 0.025). Codeine/loperamide increased mean transit time from 47.1 to 87.6 hours (n = 5), with decreased stool weight from 182 to 119 g/day. Bacterial mass decreased in all but one subject from a mean of 18.9 to 16.1 g/day (NS). There was a significant correlation between transit time and bacterial mass in all three periods (r = 0.77, p less than 0.001). Changes in transit time are shown to alter microbial growth in the human colon and result in altered stool output, on a constant diet. Factors which affect transit may be as important as diet in determining large bowel function and hence susceptibility to disease. PMID:3596341

  20. Transition.

    ERIC Educational Resources Information Center

    Thompson, Sandy, Ed.; And Others

    1990-01-01

    This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition Issues for the 1990s" (William Halloran…

  1. Transit time estimation of tunnel inflow in fractured granites

    NASA Astrophysics Data System (ADS)

    Balvín, A.; Hokr, M.; Šanda, M.; Vitvar, T.; Rálek, P.

    2012-04-01

    We study the water flow from surface to a tunnel in the average depth of 100 m to evaluate the water residence times in the fractured rock. Transport of 2H and 18O in groundwater was simulated by use of the lumped parameter approach. The area of interest is located in the Jizera Mountains near the Bedrichov municipality in the northern part of the Czech Republic. Input concentrations of 2H and 18O were measured at Uhlícská experimental catchment in a 5km distance from the tunnel. The output concentrations were measured in the water supply tunnel near Bedcichov. The tunnel is built in compact granite, it is 2600 m long and has a maximal depth of 150 m. The samples were taken from seven different groundwater seepage sites and from the channel collecting all inflow to the tunnel, in 14 days intervals in the period from February 2010 to present. The groundwater discharges were distinguished by their intensity - three dripping ones and four with continual fluxes. The residence times of the inflowing water were estimated with the dispersion model in the FLOWPC simulation program and cover the range of 2010-2011 years. In addition, we have made preliminary tests with "filtering" the infiltrated concentration data, e.g. assumption of larger ratio of winter infiltration, time shift between snowfall and snowmelt and use of soil water sampling instead of precipitation for the input. The best fit was achieved for spring V7 (for deuterium 2H: water residence time T = 23.6 months, apparent dispersion parameter Pd = 0.28 and Nash-Sutcliffe coefficient 80.3 % and for oxygen 18O: T = 30.9 months, Pd = 0.488 and N-S = 80.1 %, both for redistribution of rain), other fits were approximately 50-65 % (spring V6: T = 24.9 months, Pd = 0.26, N-S = 61.77 %; spring V1: T = 28.6 months, Pd = 0.24, N-S = 50.09 %, both for oxygen 18O). The discharge in the shallow part of the tunnel is probably supplied by flow on the soil-bedrock interface, with a quick reaction to precipitation and dry in

  2. Automatic location of L/H transition times for physical studies with a large statistical basis

    NASA Astrophysics Data System (ADS)

    González, S.; Vega, J.; Murari, A.; Pereira, A.; Dormido-Canto, S.; Ramírez, J. M.; contributors, JET-EFDA

    2012-06-01

    Completely automatic techniques to estimate and validate L/H transition times can be essential in L/H transition analyses. The generation of databases with hundreds of transition times and without human intervention is an important step to accomplish (a) L/H transition physics analysis, (b) validation of L/H theoretical models and (c) creation of L/H scaling laws. An entirely unattended methodology is presented in this paper to build large databases of transition times in JET using time series. The proposed technique has been applied to a dataset of 551 JET discharges between campaigns C21 and C26. A prediction with discharges that show a clear signature in time series is made through the locating properties of the wavelet transform. It is an accurate prediction and the uncertainty interval is ±3.2 ms. The discharges with a non-clear pattern in the time series use an L/H mode classifier based on discharges with a clear signature. In this case, the estimation error shows a distribution with mean and standard deviation of 27.9 ms and 37.62 ms, respectively. Two different regression methods have been applied to the measurements acquired at the transition times identified by the automatic system. The obtained scaling laws for the threshold power are not significantly different from those obtained using the data at the transition times determined manually by the experts. The automatic methods allow performing physical studies with a large number of discharges, showing, for example, that there are statistically different types of transitions characterized by different scaling laws.

  3. Transit Timing Observations from Kepler: VII. Potentially interesting candidate systems from Fourier-based statistical tests

    SciTech Connect

    Steffen, Jason H.; Ford, Eric B.; Rowe, Jason F.; Fabrycky, Daniel C.; Holman, Matthew J.; Welsh, William F.; Borucki, William J.; Batalha, Natalie M.; Bryson, Steve; Caldwell, Douglas A.; Ciardi, David R.; /Caltech /NASA, Ames /SETI Inst., Mtn. View

    2012-01-01

    We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.

  4. TRANSIT TIMING OBSERVATIONS FROM KEPLER. VI. POTENTIALLY INTERESTING CANDIDATE SYSTEMS FROM FOURIER-BASED STATISTICAL TESTS

    SciTech Connect

    Steffen, Jason H.; Ford, Eric B.; Rowe, Jason F.; Borucki, William J.; Bryson, Steve; Caldwell, Douglas A.; Jenkins, Jon M.; Koch, David G.; Sanderfer, Dwight T.; Seader, Shawn; Twicken, Joseph D.; Fabrycky, Daniel C.; Welsh, William F.; Batalha, Natalie M.; Ciardi, David R.; Prsa, Andrej

    2012-09-10

    We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through quarter six of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.

  5. A simple technique to rule out occlusion of right coronary artery after aortic valve surgery.

    PubMed

    Fernández, Angel L; El-Diasty, Mohammad M; Martínez, Amparo; Alvarez, Julian; García-Bengochea, José B

    2011-12-01

    Mechanical occlusion of the right coronary artery during aortic valve surgery is an infrequent but serious complication. Early recognition and expeditious management are important to reduce mortality. We developed a safe, quick, and easy technique to assess right coronary artery flow after aortic valve surgery. Direct intraoperative right coronary artery flow was measured by placing a transit-time flowmeter probe around the right coronary artery. We were able to promptly detect severe right coronary artery insufficiency in patients with acute unexpected right ventricular failure after aortic valve replacement. PMID:22115253

  6. Timing of the maturation transition in haddock Melanogrammus aeglefinus.

    PubMed

    Tobin, D; Wright, P J; O'Sullivan, M

    2010-10-01

    The timing of maturation in haddock Melanogrammus aeglefinus was examined using changes in gonad development, follicle stimulating hormone β (FSH-β) transcript expression profile, growth and condition of 1 year old females held under a common environment between the summer and winter solstices. The circumnuclear ring, cortical alveolus and vitellogenic oocyte stages were first observed in August, October and November, respectively. FSH-β transcript levels did not change significantly until September but increased markedly thereafter in maturing fish. A combined analysis of the mean oocyte diameter of the leading cohort, histological staging and FSH-β transcript profile provided evidence of a commitment to maturation by October or November. Contrary to that previously proposed for gadoid species, histological analysis of field-caught immature M. aeglefinus during the spawning season indicated that cortical alveolar, rather than circumnuclear ring, stage oocytes provided definitive evidence of maturation. A decrease in relative liver size following the summer solstice suggested a possible link between energy status and maturation. PMID:21039503

  7. TRANSIT TIMING OBSERVATIONS FROM KEPLER. I. STATISTICAL ANALYSIS OF THE FIRST FOUR MONTHS

    SciTech Connect

    Ford, Eric B.; Rowe, Jason F.; Caldwell, Douglas A.; Jenkins, Jon M.; Li Jie; Fabrycky, Daniel C.; Lissauer, Jack J.; Borucki, William J.; Bryson, Steve; Koch, David G.; Steffen, Jason H.; Batalha, Natalie M.; Dunham, Edward W.; Gautier, Thomas N.; Marcy, Geoffrey W.; McCauliff, Sean

    2011-11-01

    The architectures of multiple planet systems can provide valuable constraints on models of planet formation, including orbital migration, and excitation of orbital eccentricities and inclinations. NASA's Kepler mission has identified 1235 transiting planet candidates. The method of transit timing variations (TTVs) has already confirmed seven planets in two planetary systems. We perform a transit timing analysis of the Kepler planet candidates. We find that at least {approx}11% of planet candidates currently suitable for TTV analysis show evidence suggestive of TTVs, representing at least {approx}65 TTV candidates. In all cases, the time span of observations must increase for TTVs to provide strong constraints on planet masses and/or orbits, as expected based on N-body integrations of multiple transiting planet candidate systems (assuming circular and coplanar orbits). We find the fraction of planet candidates showing TTVs in this data set does not vary significantly with the number of transiting planet candidates per star, suggesting significant mutual inclinations and that many stars with a single transiting planet should host additional non-transiting planets. We anticipate that Kepler could confirm (or reject) at least {approx}12 systems with multiple transiting planet candidates via TTVs. Thus, TTVs will provide a powerful tool for confirming transiting planets and characterizing the orbital dynamics of low-mass planets. If Kepler observations were extended to at least seven years, then TTVs would provide much more precise constraints on the dynamics of systems with multiple transiting planets and would become sensitive to planets with orbital periods extending into the habitable zone of solar-type stars.

  8. The effect of conjunctions on the transit timing variations of exoplanets

    SciTech Connect

    Nesvorný, David; Vokrouhlický, David E-mail: vokrouhl@cesnet.cz

    2014-07-20

    We develop an analytic model for transit timing variations produced by orbital conjunctions between gravitationally interacting planets. If the planetary orbits have tight orbital spacing, which is a common case among the Kepler planets, the effect of a single conjunction can be best described as: (1) a step-like change of the transit timing ephemeris with subsequent transits of the inner planet being delayed and those of the outer planet being sped up, and (2) a discrete change in sampling of the underlying oscillations from eccentricity-related interaction terms. In the limit of small orbital eccentricities, our analytic model gives explicit equations for these effects as a function of the mass and orbital separation of planets. We point out that a detection of the conjunction effect in real data is of crucial importance for the physical characterization of planetary systems from transit timing variations.

  9. A time-dependent order parameter for ultrafast photoinduced phase transitions

    NASA Astrophysics Data System (ADS)

    Beaud, P.; Caviezel, A.; Mariager, S. O.; Rettig, L.; Ingold, G.; Dornes, C.; Huang, S.-W.; Johnson, J. A.; Radovic, M.; Huber, T.; Kubacka, T.; Ferrer, A.; Lemke, H. T.; Chollet, M.; Zhu, D.; Glownia, J. M.; Sikorski, M.; Robert, A.; Wadati, H.; Nakamura, M.; Kawasaki, M.; Tokura, Y.; Johnson, S. L.; Staub, U.

    2014-10-01

    Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent ‘order parameter’ that depends exclusively on the electronic excitation.

  10. Transit Timing Variations as a Tool for the Bayesian Characterization of Exoplanets

    NASA Astrophysics Data System (ADS)

    Ford, Eric B.; Jontof-Hutter, Daniel; Dawson, Rebekah; Fabrycky, Daniel; Mills, Sean; Ragozzine, Darin; Rogers, Leslie Anne; Shabram, Megan

    2015-08-01

    NASA's Kepler mission has revolutionized time-domain photometry with its photometric precision, high duty cycle, and long observing baseline. In addition to discovering thousands of planet candidates that pass in front of their host star, Kepler's has enabled the precise measurement of transit timing variations (TTV), deviations of transit times from a Keplerian ephemeris due to gravitational interactions among planets (or more massive bodies in the same planetary system). For dozens of planets, TTVs enable the precise characterization of planet masses and orbits, including many planets for which characterization via Doppler observations is impractical.For example, TTVs have: 1) characterized of masses of planets in systems with 2-6 transiting exoplanets, 2) measured densities for low-mass, low-density mass planets that orbit stars with periods of ~50-200 days, and provided precise measurements of orbital eccentricities even in the challenging regime of e<0.1. In addition to characterizing properties of individual planets, analysing the transit times for populations of transiting planets (including those for which no deviations from Keplerian orbits are detected) enable the characterization of the exoplanet distribution function.In both cases, attention to details of the statistical model and computational methods are essential for drawing robust conclusions. I will present selected TTV success stories, describing how these studies dealt with various statistical and computational challenges. Finally, I will describe opportunities for further improvements in the statistical analyses of transit timing variations and the potential science return.

  11. The Impact of Circumplantary Jets on Transit Spectra and Timing Offsets for Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Dobbs-Dixon, Ian; Agol, Eric; Burrows, Adam

    2012-06-01

    We present theoretical wavelength-dependent transit light curves for the giant planet HD 209458b based on a number of state-of-the-art three-dimensional radiative hydrodynamical models. By varying the kinematic viscosity in the model, we calculate observable signatures associated with the emergence of a super-rotating circumplanetary jet that strengthens with decreased viscosity. We obtain excellent agreement between our mid-transit transit spectra and existing data from Hubble and Spitzer, finding the best fit for intermediate values of viscosity. We further exploit dynamically driven differences between eastern and western hemispheres to extract the spectral signal imparted by a circumplanetary jet. We predict that (1) the transit depth should decrease as the jet becomes stronger; (2) the measured transit times should show timing offsets of up to 6 s at wavelengths with higher opacity, which increases with jet strength; (3) wavelength-dependent differences between ingress and egress spectra increase with jet strength; and (4) the color-dependent transit shape should exhibit stronger asymmetry for planets with stronger jets. These techniques and trends should be valid for other hot Jupiters as well. Observations of transit timing offsets may be accessible with current instrumentation, though the other predictions may require the capabilities of the James Webb Space Telescope and other future missions. Hydrodynamical models utilized solve the three-dimensional Navier-Stokes equations together with decoupled thermal and radiative energy equations and wavelength-dependent stellar heating.

  12. THE IMPACT OF CIRCUMPLANTARY JETS ON TRANSIT SPECTRA AND TIMING OFFSETS FOR HOT JUPITERS

    SciTech Connect

    Dobbs-Dixon, Ian; Agol, Eric; Burrows, Adam

    2012-06-01

    We present theoretical wavelength-dependent transit light curves for the giant planet HD 209458b based on a number of state-of-the-art three-dimensional radiative hydrodynamical models. By varying the kinematic viscosity in the model, we calculate observable signatures associated with the emergence of a super-rotating circumplanetary jet that strengthens with decreased viscosity. We obtain excellent agreement between our mid-transit transit spectra and existing data from Hubble and Spitzer, finding the best fit for intermediate values of viscosity. We further exploit dynamically driven differences between eastern and western hemispheres to extract the spectral signal imparted by a circumplanetary jet. We predict that (1) the transit depth should decrease as the jet becomes stronger; (2) the measured transit times should show timing offsets of up to 6 s at wavelengths with higher opacity, which increases with jet strength; (3) wavelength-dependent differences between ingress and egress spectra increase with jet strength; and (4) the color-dependent transit shape should exhibit stronger asymmetry for planets with stronger jets. These techniques and trends should be valid for other hot Jupiters as well. Observations of transit timing offsets may be accessible with current instrumentation, though the other predictions may require the capabilities of the James Webb Space Telescope and other future missions. Hydrodynamical models utilized solve the three-dimensional Navier-Stokes equations together with decoupled thermal and radiative energy equations and wavelength-dependent stellar heating.

  13. Transit times and age distributions for reservoir models represented as nonlinear non-autonomuous systems

    NASA Astrophysics Data System (ADS)

    Müller, Markus; Meztler, Holger; Glatt, Anna; Sierra, Carlos

    2016-04-01

    We present theoretical methods to compute dynamic residence and transit time distributions for non-autonomous systems of pools governed by coupled nonlinear differential equations. Although transit time and age distributions have been used to describe reservoir models for a long time, a closer look to their assumptions reveals two major restrictions of generality in previous studies. First, the systems are assumed to be in equilibrium; and second, the equations under consideration are assumed to be linear. While both these assumptions greatly ease the computation and interpretation of transit time and age distributions they are not applicable to a wide range of problems. Moreover, the transfer of previous results learned from linear systems in steady state to the more complex nonlinear non-autonomous systems that do not even need to have equilibria, can be dangerously misleading. Fortunately the topic of time dependent age and transit time distributions has received some attention recently in hydrology, we aim to compute these distributions for systems of multiple reservoirs. We will discuss how storage selection functions can augment the information represented in an ODE system describing a system of reservoirs. We will present analytical and numerical algorithms and a Monte Carlo simulator to compute solutions for system transit time and age distributions for system-wide storage selection functions including the most simple, but important case of well mixed pools.

  14. Attenuation of systolic blood pressure and pulse transit time hysteresis during exercise and recovery in cardiovascular patients.

    PubMed

    Liu, Qing; Yan, Bryan P; Yu, Cheuk-Man; Zhang, Yuan-Ting; Poon, Carmen C Y

    2014-02-01

    Pulse transit time (PTT) is a cardiovascular parameter of emerging interest due to its potential to estimate blood pressure (BP) continuously and without a cuff. Both linear and nonlinear equations have been used in the estimation of BP based on PTT. This study, however, demonstrates that there is a hysteresis phenomenon between BP and PTT during and after dynamic exercise. A total of 46 subjects including 16 healthy subjects, 13 subjects with one or more cardiovascular risk factors, and 17 patients with cardiovascular disease underwent graded exercise stress test. PTT was measured from electrocardiogram and photoplethysmogram of the left index finger of the subject, i.e., a pathway that includes predominately aorta, brachial, and radial arteries. The results of this study showed that, for the same systolic BP (SBP), PTT measured during exercise was significantly larger than PTT measured during recovery for all subject groups. This hysteresis was further quantified as both normalized area bounded by the SBP-PTT relationship (AreaN) and SBP difference at PTT during peak exercise plus 20 ms (ΔSBP20). Significant attenuation of both AreaN (p <; 0.05) and ΔSBP20 (p <; 0.01) is observed in cardiovascular patients compared with healthy subjects, independent of resting BP. Since the SBP-PTT relationship are determined by the mechanical properties of arterial wall, which is predominately mediated by the sympathetic nervous system through altered vascular smooth muscle (VSM) tone during exercise, results of this study are consistent with the previous findings of autonomic nervous dysfunction in cardiovascular patients. We further conclude that VSM tone has a nonnegligible influence on the BP-PTT relationship and thus should be considered in the PTT-based BP estimation. PMID:24158470

  15. Salt-tracer experiments to measure hyporheic transit time distributions in gravel-bed sediments

    NASA Astrophysics Data System (ADS)

    van der Perk, M.; Petticrew, E. L.; Owens, P. N.; Hulsman, R.; Wubben, L.

    2009-04-01

    We performed a series of tracer experiments in large outdoor flumes at the Quesnel River Research Centre, Likely, BC, Canada to quantify the hyporheic transit time distribution in gravel bed sediments. For this purpose, an 18.9 m x 2 m flume was filled with a 30 cm thick layer of well-sorted gravel with a d50 of 39.1 mm. The average longitudinal gradient of the gravel bed was 0.05% The flumes were filled with aerated local groundwater, so that a standing water layer of 20 cm depth over the gravel bed was established. Subsequently, dissolved common salt was added until the water reached an electrical conductivity (EC) between 450 and 550 µS/cm. The flumes were equilibrated overnight to ensure a uniform distribution of the salt concentration across the flume. At the start of each experiment local groundwater (EC = 150 µS/cm) was discharged at a rate of approximately 16 l/s at the upper end of the flume. At 10 m downstream from the inlet the EC was monitored in the water layer until the EC remained constant at a value close to the background value of about 150 µS/cm. The experiment was replicated three times. The measured breakthrough curves were used to calculate the overall transit time distributions of water in the 10 m stretch of the flume. The transit time distribution in the water layer was calculated using the longitudinal dispersion coefficient estimated using the empirical equation of Fischer et al. (1979). For the transit time distributions within the gravel layer we assumed a probability density function as proposed by Marion and Zaramella (2005). These hyporheic transit time distributions were estimated using least-squares deconvolution of the overall transit time distributions. The fitted overall transit time distributions corresponded fairly well to the ‘observed' distributions. The 10th percentile of the hyporheic transit time distributions in the 10 m stretch of the flume varied between 45 s and 65 s. The median transit time ranged between 200 s

  16. Relationships between the transit time of water and the fluxes of reactive elements (Invited)

    NASA Astrophysics Data System (ADS)

    Maher, K.; Druhan, J. L.; Nelson, J.

    2013-12-01

    The movement of water is widely a recognized control on the chemical weathering rates of landscapes. However, the extent to which mass transfer during chemical weathering is determined by the subsurface structure and heterogeneity remains poorly quantified. As a result, most geochemical models that seek to explain solute fluxes from catchments cannot predict the commonly observed relationships between the concentration of reactive solutes and stream discharge. Because the solute generation from weathering reactions along a single flow path is thermodynamically constrained (i.e., the concentration of solute will increase until chemical equilibrium is reached), the transit time of water is a critical control on solute fluxes. The reactive solute composition of waters in the stream is the flux-weighted average of the ensemble of these flow paths and is thus strongly linked to the transit time distribution. An alternative view is that the reactive solutes present a survey of the subsurface flowpaths because the chemical reactions rates provide an internal clock. We present several different approaches of varying complexity, from reactive transport simulations of heterogeneous flow fields to analytical solutions that link the extent of reaction progress to a given transit time distribution, and compare these approaches to a variety of datasets from catchments. Using inverse methods, we further evaluate which, and under what conditions, reactive tracers can be used to evaluate the mean transit time and distribution. Results for small catchments indicate that the solute compositions are a strong function of mean transit time, but the form of the transit time distribution cannot be distinguished using only concentration-discharge relationships. Collectively our results suggest that weathering fluxes from landscapes are controlled by the balance between the mean transit time and the mean reactive surface area. Despite the inherent challenges, coupling measures of water age

  17. Discrimination of human coronary artery atherosclerotic lipid-rich lesions by time-resolved laser-induced fluorescence spectroscopy.

    PubMed

    Marcu, L; Fishbein, M C; Maarek, J M; Grundfest, W S

    2001-07-01

    Lesion composition plays a significant role in atherosclerotic lesion instability and rupture. Current clinical techniques cannot fully characterize lesion composition or accurately identify unstable lesions. This study investigates the use of time-resolved fluorescence spectroscopy for unstable atherosclerotic lesion diagnosis. The fluorescence of human coronary artery samples was induced with nitrogen laser and detected in the 360- to 510-nm wavelength range. The samples were sorted into 7 groups according to the AHA classification: normal wall and types I, II(a) (fatty streaks), III (preatheroma), IV (atheroma), V(a) (fibrous), and V(b) (calcified) lesions. Spectral intensities and time-dependent parameters [average lifetime tau(f); decay constants: tau(1) (fast-term), tau(2) (slow-term), A(1) (fast-term amplitude contribution)] derived from the time-resolved spectra of coronary samples were used for tissue characterization. We determined that a few intensity values at longer wavelengths (>430 nm) and time-dependent parameters at peak emission region (390 nm) discriminate between all types of arterial samples except between normal wall and type I lesions. The lipid-rich lesions (more unstable) can be discriminated from fibrous lesions (more stable) on the basis of time-dependent parameters (lifetime and fast-term decay). We inferred that features of lipid fluorescence are reflected on lipid-rich lesion emission. Our results demonstrate that analysis of the time-resolved spectra may be used to enhance the discrimination between different grades of atherosclerotic lesions and provide a means of discrimination between lipid-rich and fibrous lesions. PMID:11451759

  18. Finite-time quantum-to-classical transition for a Schroedinger-cat state

    SciTech Connect

    Paavola, Janika; Hall, Michael J. W.; Paris, Matteo G. A.; Maniscalco, Sabrina

    2011-07-15

    The transition from quantum to classical, in the case of a quantum harmonic oscillator, is typically identified with the transition from a quantum superposition of macroscopically distinguishable states, such as the Schroedinger-cat state, into the corresponding statistical mixture. This transition is commonly characterized by the asymptotic loss of the interference term in the Wigner representation of the cat state. In this paper we show that the quantum-to-classical transition has different dynamical features depending on the measure for nonclassicality used. Measures based on an operatorial definition have well-defined physical meaning and allow a deeper understanding of the quantum-to-classical transition. Our analysis shows that, for most nonclassicality measures, the Schroedinger-cat state becomes classical after a finite time. Moreover, our results challenge the prevailing idea that more macroscopic states are more susceptible to decoherence in the sense that the transition from quantum to classical occurs faster. Since nonclassicality is a prerequisite for entanglement generation our results also bridge the gap between decoherence, which is lost only asymptotically, and entanglement, which may show a ''sudden death''. In fact, whereas the loss of coherences still remains asymptotic, we emphasize that the transition from quantum to classical can indeed occur at a finite time.

  19. Transiting planets as a precision clock to constrain the time variation of the gravitational constant

    NASA Astrophysics Data System (ADS)

    Masuda, Kento; Suto, Yasushi

    2016-06-01

    Analysis of transit times in exoplanetary systems accurately provides an instantaneous orbital period, P(t), of their member planets. A long-term monitoring of those transiting planetary systems puts limits on the variability of P(t), which are translated into the constraints on the time variation of the gravitational constant G. We apply this analysis to 10 transiting systems observed by the Kepler spacecraft, and find that ΔG/G ≲ 5 × 10- 6 for 2009-2013, or dot{G}/G ≲ 10^{-6}yr-1 if dot{G} is constant. While the derived limit is weaker than those from other analyses, it is complementary to them and can be improved by analyzing numerous transiting systems that are continuously monitored.

  20. Time-delayed transition of normal-to-abnormal glow in pin-to-water discharge

    NASA Astrophysics Data System (ADS)

    Yoon, S.-Y.; Byeon, Y.-S.; Yoo, S.; Hong, E. J.; Kim, S. B.; Yoo, S. J.; Ryu, S.

    2016-08-01

    Time-delayed transition of normal-to-abnormal glow was investigated in discharge between spoke-like pins and ultrapure water by applying AC-driven power at a frequency of 14.3 kHz at atmospheric pressure. The normal-to-abnormal transition can be recognized from the slope changes of current density, gas temperature, electrode temperature, and OH density. The slope changes took place in tens of minutes rather than just after discharge, in other words, the transition was delayed. The time-delay of the transition was caused by the interaction between the plasma and water. The plasma affected water properties, and then the water affected plasma properties.

  1. The detection and characterization of a nontransiting planet by transit timing variations.

    PubMed

    Nesvorný, David; Kipping, David M; Buchhave, Lars A; Bakos, Gáspár Á; Hartman, Joel; Schmitt, Allan R

    2012-06-01

    The Kepler mission is monitoring the brightness of ~150,000 stars, searching for evidence of planetary transits. As part of the Hunt for Exomoons with Kepler (HEK) project, we report a planetary system with two confirmed planets and one candidate planet discovered with the publicly available data for KOI-872. Planet b transits the host star with a period P(b) = 33.6 days and exhibits large transit timing variations indicative of a perturber. Dynamical modeling uniquely detects an outer nontransiting planet c near the 5:3 resonance (P(c) = 57.0 days) with a mass 0.37 times that of Jupiter. Transits of a third planetary candidate are also found: a 1.7-Earth radius super-Earth with a 6.8-day period. Our analysis indicates a system with nearly coplanar and circular orbits, reminiscent of the orderly arrangement within the solar system. PMID:22582018

  2. Not ready for prime time: transitional events in the extremely preterm infant.

    PubMed

    Armentrout, Debra

    2014-01-01

    Successful transition from intrauterine to extrauterine life involves significant physiologic changes. The majority of these changes occur relatively quickly during those first moments following delivery; however, transition for the extremely preterm infant occurs over a longer period of time. Careful assessment and perceptive interventions on the part of neonatal care providers is essential as the extremely preterm infant adjusts to life outside the womb. This article will focus on respiratory, cardiovascular, gastrointestinal, and neurologic transitional events experienced by the extremely premature infant. PMID:24781773

  3. Arterial embolism

    MedlinePlus

    ... the artery (arterial bypass) to create a second source of blood supply Clot removal through a balloon catheter placed into the affected artery or through open surgery on the artery (embolectomy) Opening of the ...

  4. Calibration of pulse transit time through a cable for EAS experiments

    NASA Astrophysics Data System (ADS)

    Qian, Xiang-Li; Chang, Jin-Fan; Feng, Cun-Feng; Feng, Zhao-Yang; Gou, Quan-Bu; Guo, Yi-Qing; Hu, Hong-Bo; Liu, Cheng; Wang, Zheng; Xue, Liang; Zhang, Xue-Yao; Zhang, Yi

    2014-06-01

    In ground-based extensive air shower experiments, the direction and energy are reconstructed by measuring the relative arrival time of secondary particles, and the energy they deposit. The measurement precision of the arrival time is crucial for determination of the angular resolution. For this purpose, we need to obtain a precise relative time offset for each detector and to apply the calibration process. The time offset is associated with the photomultiplier tube, cable, relevant electronic circuits, etc. In view of the transit time through long cables being heavily dependent on the ambient temperature, a real-time calibration method for the cable transit time is investigated in this paper. Even with a poor-resolution time-to-digital converter, this method can achieve high precision. This has been successfully demonstrated with the Front-End-Electronic board used in the Daya Bay neutrino experiment.

  5. Transit times and mean ages for nonautonomous and autonomous compartmental systems

    DOE PAGESBeta

    Rasmussen, Martin; Hastings, Alan; Smith, Matthew J.; Agusto, Folashade B.; Chen-Charpentier, Benito M.; Hoffman, Forrest M.; Jiang, Jiang; Todd-Brown, Katherine E. O.; Wang, Ying; Wang, Ying -Ping; et al

    2016-04-01

    In this study, we develop a theory for transit times and mean ages for nonautonomous compartmental systems. Using the McKendrick–von Förster equation, we show that the mean ages of mass in a compartmental system satisfy a linear nonautonomous ordinary differential equation that is exponentially stable. We then define a nonautonomous version of transit time as the mean age of mass leaving the compartmental system at a particular time and show that our nonautonomous theory generalises the autonomous case. We apply these results to study a nine-dimensional nonautonomous compartmental system modeling the terrestrial carbon cycle, which is a modification of themore » Carnegie–Ames–Stanford approach model, and we demonstrate that the nonautonomous versions of transit time and mean age differ significantly from the autonomous quantities when calculated for that model.« less

  6. New geometric transition as origin of particle production in time-dependent backgrounds

    NASA Astrophysics Data System (ADS)

    Kim, Sang Pyo

    2013-10-01

    By extending the quantum evolution of a scalar field in time-dependent backgrounds to the complex-time plane and transporting the in-vacuum along a closed path, we argue that the geometric transition from the simple pole at infinity determines the multi-pair production depending on the winding number. We apply the geometric transition to Schwinger mechanism in the time-dependent vector potential for a constant electric field and to Gibbons-Hawking particle production in the planar coordinates of a de Sitter space.

  7. Prompting technologies: A comparison of time-based and context-aware transition-based prompting

    PubMed Central

    Robertson, Kayela; Rosasco, Cody; Feuz, Kyle; Schmitter-Edgecombe, Maureen; Cook, Diane

    2016-01-01

    BACKGROUND While advancements in technology have encouraged the development of novel prompting systems to support cognitive interventions, little research has evaluated the best time to deliver prompts, which may impact the effectiveness of these interventions. OBJECTIVE This study examined whether transition-based context prompting (prompting an individual during task transitions) is more effective than traditional fixed time-based prompting. METHODS Participants were 42 healthy adults who completed 12 different everyday activities, each lasting 1–7 minutes, in an experimental smart home testbed and received prompts to record the completed activities from an electronic memory notebook. Half of the participants were delivered prompts during activity transitions, while the other half received prompts every 5 minutes. Participants also completed Likert-scale ratings regarding their perceptions of the prompting system. RESULTS Results revealed that participants in the transition-based context prompting condition responded to the first prompt more frequently and rated the system as more convenient, natural, and appropriate compared to participants in the time-based condition. CONCLUSIONS Our findings suggest that prompting during activity transitions produces higher adherence to the first prompt and more positive perceptions of the prompting system. This is an important finding given the benefits of prompting technology and the possibility of improving cognitive interventions by using context-aware transition prompting. PMID:26409520

  8. Timing Preferences for Women's Family-Life Transitions: Intergenerational Transmission among Migrants and Dutch

    ERIC Educational Resources Information Center

    de Valk, Helga A. G.; Liefbroer, Aart C.

    2007-01-01

    This study examines the transmission of preferences regarding the timing of family-life transitions of women among migrant and native Dutch families. We study how and to what extent parental preferences, migrant origin, and family characteristics affect the child's timing preferences. We use parent and child data (N = 1,290) from the Netherlands…

  9. Timing of Parenthood in Relation to Other Life Transitions and Adult Social Functioning

    ERIC Educational Resources Information Center

    Kokko, Katja; Pulkkinen, Lea; Mesiainen, Paivi

    2009-01-01

    The timing of having one's first child, in relation to the timing of other transitions into adulthood and to social functioning, was investigated based on the Finnish Jyvaskyla Longitudinal Study of Personality and Social Development, conducted from age 8 (173 females and 196 males) to 42. Results showed that in women, relatively early (less than…

  10. Non-invasive monitoring of pulmonary artery pressure from timing information by EIT: experimental evaluation during induced hypoxia.

    PubMed

    Proença, Martin; Braun, Fabian; Solà, Josep; Adler, Andy; Lemay, Mathieu; Thiran, Jean-Philippe; Rimoldi, Stefano F

    2016-06-01

    Monitoring of pulmonary artery pressure (PAP) in pulmonary hypertensive patients is currently limited to invasive solutions. We investigate a novel non-invasive approach for continuous monitoring of PAP, based on electrical impedance tomography (EIT), a safe, low-cost and non-invasive imaging technology. EIT recordings were performed in three healthy subjects undergoing hypoxia-induced PAP variations. The pulmonary pulse arrival time (PAT), a timing parameter physiologically linked to the PAP, was automatically calculated from the EIT signals. Values were compared to systolic PAP values from Doppler echocardiography, and yielded strong correlation scores ([Formula: see text]) for all three subjects. Results suggest the feasibility of non-invasive, unsupervised monitoring of PAP. PMID:27212013

  11. Pulse-echo ultrasound transit time spectroscopy: A comparison of experimental measurement and simulation prediction.

    PubMed

    Wille, Marie-Luise; Almualimi, Majdi A; Langton, Christian M

    2016-01-01

    Considering ultrasound propagation through complex composite media as an array of parallel sonic rays, a comparison of computer-simulated prediction with experimental data has previously been reported for transmission mode (where one transducer serves as transmitter, the other as receiver) in a series of 10 acrylic step-wedge samples, immersed in water, exhibiting varying degrees of transit time inhomogeneity. In this study, the same samples were used but in pulse-echo mode, where the same ultrasound transducer served as both transmitter and receiver, detecting both 'primary' (internal sample interface) and 'secondary' (external sample interface) echoes. A transit time spectrum was derived, describing the proportion of sonic rays with a particular transit time. A computer simulation was performed to predict the transit time and amplitude of various echoes created, and compared with experimental data. Applying an amplitude-tolerance analysis, 91.7% ± 3.7% of the simulated data were within ±1 standard deviation of the experimentally measured amplitude-time data. Correlation of predicted and experimental transit time spectra provided coefficients of determination (R(2)%) ranging from 100.0% to 96.8% for the various samples tested. The results acquired from this study provide good evidence for the concept of parallel sonic rays. Furthermore, deconvolution of experimental input and output signals has been shown to provide an effective method to identify echoes otherwise lost due to phase cancellation. Potential applications of pulse-echo ultrasound transit time spectroscopy include improvement of ultrasound image fidelity by improving spatial resolution and reducing phase interference artefacts. PMID:26586528

  12. Characterization of post mortem arterial tissue using time-resolved photoacoustic spectroscopy at 436, 461 and 532 nm.

    PubMed

    Beard, P C; Mills, T N

    1997-01-01

    Time-resolved photoacoustic spectroscopy has been used to characterize post mortem arterial tissue for the purpose of discriminating between normal and atheromatous areas of tissue. Ultrasonic thermoelastic waves were generated in post mortem human aorta by the absorption of nanosecond laser pulses at 436, 461 and 532 nm produced by a frequency doubled Q-switched Nd:YAG laser in conjunction with a gas filled Raman cell. A PVDF membrane hydrophone was used to detect the thermoelastic waves. At 436 nm, differences in the photoacoustic signatures of normal tissue and atherorma were found to be highly variable. At 461 nm, there was a clear and reproducible difference between the photacoustic response of atheroma and normal tissue as a result of increased optical attenuation in atheroma. At 532 nm, the generation of subsurface thermoelastic waves provided a means of determining the structure and thickness of the tissue sample. It is suggested that pulsed photoacoustic spectroscopy at 461 and 532 nm may find application in characterizing arterial tissue in situ by providing information about both the composition and thickness of the vessel wall. PMID:9015817

  13. Determining the architecture of the Kepler-297 system using transit timing variations

    NASA Astrophysics Data System (ADS)

    Diamond-Lowe, Hannah; Stevenson, Kevin B.; Fabrycky, Daniel; Ballard, Sarah; Agol, Eric; Bean, Jacob; Holman, Matthew J.; Ragozzine, Darin

    2015-01-01

    It is essential to explore the architectures of exoplanetary systems as we attempt to understand planet formation histories and determine the rate of occurrence of habitable-zone rocky planets. We focus on the Kepler-297 system which hosts three transiting planets, Kepler-297b, Kepler-297c, and KOI-1426.03. We re-analyze extant Kepler data of the system, as well as new Spitzer data of Kepler-297c, to constrain the transit time variations (TTVs) of the three transiting planets in the system. We feed these results into a dynamical analysis in which the TTVs of the transiting planets constrain their orbital parameters, as well as those of potential non-transiting planets. The gravitational interactions between the Kepler-297 planets allow us to derive their mass ratios. We find that the orbital parameters of the three transiting planets are well-fit by a model that includes a non-transiting fourth planet outside of the three transitors. We are also able to constrain the orbital parameters of the outer-most transitor, thereby confirming it as the planet Kepler-297d.

  14. Decreasing transition times in elementary school classrooms: Using computer-assisted instruction to automate intervention components.

    PubMed

    Hine, Jeffrey F; Ardoin, Scott P; Foster, Tori E

    2015-09-01

    Research suggests that students spend a substantial amount of time transitioning between classroom activities, which may reduce time spent academically engaged. This study used an ABAB design to evaluate the effects of a computer-assisted intervention that automated intervention components previously shown to decrease transition times. We examined the effects of the intervention on the latency to on-task behavior of 4 students in 2 classrooms. Data also were collected on students' on-task behavior during activities and teachers' use of prompts and praise statements. Implementation of the intervention substantially decreased students' latencies to on-task behavior and increased on-task behavior overall. Further, the 2 teachers used fewer prompts to cue students to transition and stay on task and provided more praise during intervention phases. We discuss how automating classroom interventions may affect student and teacher behavior as well as how it may increase procedural fidelity. PMID:26223859

  15. Biomagnetic techniques for evaluating gastric emptying, peristaltic contraction and transit time

    PubMed Central

    la Roca-Chiapas, Jose María De; Cordova-Fraga, Teodoro

    2011-01-01

    Biomagnetic techniques were used to measure motility in various parts of the gastrointestinal (GI) tract, particularly a new technique for detecting magnetic markers and tracers. A coil was used to enhance the signal from a magnetic tracer in the GI tract and the signal was detected using a fluxgate magnetometer or a magnetoresistor in an unshielded room. Estimates of esophageal transit time were affected by the position of the subject. The reproducibility of estimates derived using the new biomagnetic technique was greater than 85% and it yielded estimates similar to those obtained using scintigraphy. This technique is suitable for studying the effect of emotional state on GI physiology and for measuring GI transit time. The biomagnetic technique can be used to evaluate digesta transit time in the esophagus, stomach and colon, peristaltic frequency and gastric emptying and is easy to use in the hospital setting. PMID:22025978

  16. Biomagnetic techniques for evaluating gastric emptying, peristaltic contraction and transit time.

    PubMed

    la Roca-Chiapas, Jose María De; Cordova-Fraga, Teodoro

    2011-10-15

    Biomagnetic techniques were used to measure motility in various parts of the gastrointestinal (GI) tract, particularly a new technique for detecting magnetic markers and tracers. A coil was used to enhance the signal from a magnetic tracer in the GI tract and the signal was detected using a fluxgate magnetometer or a magnetoresistor in an unshielded room. Estimates of esophageal transit time were affected by the position of the subject. The reproducibility of estimates derived using the new biomagnetic technique was greater than 85% and it yielded estimates similar to those obtained using scintigraphy. This technique is suitable for studying the effect of emotional state on GI physiology and for measuring GI transit time. The biomagnetic technique can be used to evaluate digesta transit time in the esophagus, stomach and colon, peristaltic frequency and gastric emptying and is easy to use in the hospital setting. PMID:22025978

  17. The Transit-Time Distribution from the Northern Hemisphere Midlatitude Surface

    NASA Technical Reports Server (NTRS)

    Orbe, Clara; Waugh, Darryn W.; Newman, Paul A.; Strahan, Susan; Steenrod, Stephen

    2015-01-01

    The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here we present an analysis of the transit time distribution (TTD) since air last contacted the northern midlatitude surface layer, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model. We find that throughout the troposphere the TTD is characterized by long flat tails that reflect the recirculation of old air from the Southern Hemisphere and results in mean ages that are significantly larger than the modal age. Key aspects of the TTD -- its mode, mean and spectral width -- are interpreted in terms of tropospheric dynamics, including seasonal shifts in the location and strength of tropical convection and variations in quasi-isentropic transport out of the northern midlatitude surface layer. Our results indicate that current diagnostics of tropospheric transport are insufficient for comparing model transport and that the full distribution of transit times is a more appropriate constraint.

  18. Effect of pinaverium bromide on jejunal motility and colonic transit time in healthy humans.

    PubMed

    Bouchoucha, M; Salles, J P; Fallet, M; Frileux, P; Cugnenc, P H; Barbier, J P

    1992-01-01

    Pinaverium bromide is a specific calcium channel blocker used in the treatment of irritable bowel syndrome (IBS) for its spasmolytic activity. The aim of the present study was to evaluate the effect of orally administered pinaverium bromide on jejunal motility and total and segmental colonic transit time in control subjects. Gastrointestinal studies were performed in 10 healthy volunteers (30 +/- 3 years), before and after a treatment phase of 14 days (150 mg/d). Jejunal motility was measured by prolonged manometry (14 h) and colonic transit time by a multiple ingestion, single marker technique. No significant modification of phase III of the migrating motor complexes was demonstrated. On the contrary, a significant (p < 0.01) but weak decrease of the frequency of contraction was found. Unlike previous studies, no decrease of total or segmental colonic transit time was demonstrated. PMID:1421047

  19. Time scheduling of transit systems with transfer considerations using genetic algorithms.

    PubMed

    Deb, K; Chakroborty, P

    1998-01-01

    Scheduling of a bus transit system must be formulated as an optimization problem, if the level of service to passengers is to be maximized within the available resources. In this paper, we present a formulation of a transit system scheduling problem with the objective of minimizing the overall waiting time of transferring and nontransferring passengers while satisfying a number of resource- and service-related constraints. It is observed that the number of variables and constraints for even a simple transit system (a single bus station with three routes) is too large to tackle using classical mixed-integer optimization techniques. The paper shows that genetic algorithms (GAs) are ideal for these problems, mainly because they (i) naturally handle binary variables, thereby taking care of transfer decision variables, which constitute the majority of the decision variables in the transit scheduling problem; and (ii) allow procedure-based declarations, thereby allowing complex algorithmic approaches (involving if then-else conditions) to be handled easily. The paper also shows how easily the same GA procedure with minimal modifications can handle a number of other more pragmatic extensions to the simple transit scheduling problem: buses with limited capacity, buses that do not arrive exactly as per scheduled times, and a multiple-station transit system having common routes among bus stations. Simulation results show the success of GAs in all these problems and suggest the application of GAs in more complex scheduling problems. PMID:10021738

  20. Nonlinear light behaviors near phase transition in non-parity-time-symmetric complex waveguides.

    PubMed

    Nixon, Sean; Yang, Jianke

    2016-06-15

    Many classes of non-parity-time (PT)-symmetric waveguides with arbitrary gain and loss distributions still possess all-real linear spectrum or exhibit phase transition. In this Letter, nonlinear light behaviors in these complex waveguides are probed analytically near a phase transition. Using multi-scale perturbation methods, a nonlinear ordinary differential equation (ODE) is derived for the light's amplitude evolution. This ODE predicts that a single class of these non-PT-symmetric waveguides supports soliton families and amplitude-oscillating solutions both above and below linear phase transition, in close analogy with PT-symmetric systems. For the other classes of waveguides, the light's intensity always amplifies under the effect of nonlinearity, even if the waveguide is below the linear phase transition. These analytical predictions are confirmed by direct computations of the full system. PMID:27304279

  1. Nonlinear light behaviors near phase transition in non-parity-time-symmetric complex waveguides

    NASA Astrophysics Data System (ADS)

    Nixon, Sean; Yang, Jianke

    2016-06-01

    Many classes of non-parity-time (PT) symmetric waveguides with arbitrary gain and loss distributions still possess all-real linear spectrum or exhibit phase transition. In this article, nonlinear light behaviors in these complex waveguides are probed analytically near a phase transition. Using multi-scale perturbation methods, a nonlinear ordinary differential equation (ODE) is derived for the light's amplitude evolution. This ODE predicts that the first class of these non-PT-symmetric waveguides support continuous families of solitons and robust amplitude-oscillating solutions both above and below phase transition, in close analogy with PT-symmetric systems. For the other classes of waveguides, the light's intensity always amplifies under the effect of nonlinearity even if the waveguide is below phase transition. These analytical predictions are confirmed by direct computations of the full system.

  2. Statistical stage transition detection method for small sample gene expression time series data.

    PubMed

    Tominaga, Daisuke

    2014-08-01

    In terms of their internal (genetic) and external (phenotypic) states, living cells are always changing at varying rates. Periods of stable or low rate of change are often called States, Stages, or Phases, whereas high-rate periods are called Transitions or Transients. While states and transitions are observed phenotypically, such as cell differentiation, cancer progression, for example, are related with gene expression levels. On the other hand, stages of gene expression are definable based on changes of expression levels. Analyzing relations between state changes of phenotypes and stage transitions of gene expression levels is a general approach to elucidate mechanisms of life phenomena. Herein, we propose an algorithm to detect stage transitions in a time series of expression levels of a gene by defining statistically optimal division points. The algorithm shows detecting ability for simulated datasets. An annotation based analysis on detecting results for a dataset of initial development of Caenorhabditis elegans agrees with that are presented in the literature. PMID:24960588

  3. Real‐time three‐dimensional dobutamine stress echocardiography for coronary artery disease diagnosis: validation with coronary angiography

    PubMed Central

    Aggeli, Constadina; Giannopoulos, Georgios; Misovoulos, Platon; Roussakis, George; Christoforatou, Euaggelia; Kokkinakis, Christos; Brili, Stela; Stefanadis, Christodoulos

    2007-01-01

    Objective To compare real‐time three‐dimensional echocardiography (RT3DE) with two‐dimensional dobutamine stress echocardiography (2DE) for the detection of myocardial ischaemia, with angiographic validation of the results. Methods 56 patients (mean (SD) age 64.5 (6.2) years, 38 males), referred for coronary angiography, were examined by 2DE and RT3DE during the same dobutamine stress protocol. Results All 56 patients completed the stress protocol uneventfully. The mean (SD) acquisition time for the necessary views to evaluate all segments was 26.3 (2.5) s for RT3DE and 58.8 (3.7) s for 2DE (p<0.001). At peak stress, RT3DE had a higher wall‐motion score index (1.25 (0.24) by 2DE, 1.30 (0.27) by RT3DE; p = 0.014). The regional wall‐motion score for the four apical segments at peak stress was compared; it was 1.35 (0.55) by 2DE and 1.52 (0.69) by RT3DE (p = 0.003). The diagnostic parameters of 2DE versus RT3DE were: sensitivity 73% vs 78%, specificity 93% vs 89% and overall accuracy 86% vs 85%, respectively. In the left anterior descending artery territory, in particular, where RT3DE had higher regional wall‐motion scores, it showed a tendency towards higher sensitivity (85% vs 78%), although this difference did not achieve statistical significance. Conclusion RT3DE identifies wall‐motion abnormalities more readily in the apical region than 2DE, which may explain the tendency towards higher sensitivity in the left anterior descending artery territory. RT3DE results were validated using angiography as reference and findings indicate diagnostic equivalence to 2DE, with the advantage of considerable shorter acquisition times. PMID:17085530

  4. Mean transit times in contrasting headwater catchments from southeast Australia determined using Tritium

    NASA Astrophysics Data System (ADS)

    Cartwright, Ian; Morgenstern, Uwe; Irvine, Dylan

    2016-04-01

    Headwater streams contribute a significant proportion of the total discharge of many river systems. However, despite their importance, the time taken for rainfall to pass through the catchment into the streams (the transit time) in headwater catchments is largely unknown as are the catchment characteristics (such as drainage density, topography, landuse, or geology) that determine variations in transit times. Because the peak in Tritium activities in rainfall produced by atmospheric nuclear tests in the1950's and 1960's (the "bomb-pulse") was several orders of magnitude lower in the southern hemisphere than in the northern hemisphere, Tritium activities of remnant bomb pulse water in the southern hemisphere have decayed below those of modern rainfall. This allows mean transit times to be estimated from single Tritium measurements. Here we use Tritium to estimate transit times of water contributing to perennial streams in the adjacent upper catchments of the Yarra and Latrobe Rivers (southeast Australia). Samples were collected at varying flow from six headwater tributary sites in the Latrobe catchment, which is largely forested and four tributaries in the Yarra catchment which has been extensively cleared for dryland agriculture. The lowest Tritium activities were recorded during summer baseflow conditions and are between 1.25 and 1.75 TU, these are significantly below the Tritium activity of local rainfall (~2.8 TU). Mean transit times calculated using an exponential-piston flow lumped parameter model are 21 to 47 years. Tritium activities during the recession periods following winter high flows are higher (1.54 to 2.1 TU), which may reflect either the dilution of a baseflow component with recent surface runoff or mobilisation of different stores of water with different residence times (e.g., from the soils or the regolith) from within the catchment. The variation of major ion concentrations with discharge suggests it is more likely that that different stores of

  5. Gender Transitions in Later Life: The Significance of Time in Queer Aging

    PubMed Central

    Fabbre, Vanessa D.

    2014-01-01

    Concepts of time are ubiquitous in studies of aging. This article integrates an existential perspective on time with a notion of queer time based on the experiences of older transgender persons who contemplate or pursue a gender transition in later life. Interviews were conducted with male-to-female identified persons aged 50 years or older (N=22), along with participant observation at three national transgender conferences (N=170 hours). Interpretive analyses suggest that an awareness of “time left to live” and a feeling of “time served” play a significant role in later life development and help expand gerontological perspectives on time and queer aging. PMID:24798691

  6. Transition from winnerless competition to synchronization in time-delayed neuronal motifs

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Li, P. J.; Wu, F. P.; Wu, W. J.; Jiang, M.; Chen, L.; Qi, G. X.; Huang, H. B.

    2012-03-01

    The dynamics of brain functional motifs are studied. It is shown that different rhythms can occur in the motifs when time delay is taken into account. These rhythms include synchronization, winnerless competition (WLC) and "two plus one" (TPO). The main discovery is that the transition from WLC to synchronization can be induced simply by time delay. It is also concluded that some medium time delay is needed to achieve WLC in the realistic case. The motifs composed of heterogeneous neurons are also considered.

  7. A Time Integration Algorithm Based on the State Transition Matrix for Structures with Time Varying and Nonlinear Properties

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2003-01-01

    A variable order method of integrating the structural dynamics equations that is based on the state transition matrix has been developed. The method has been evaluated for linear time variant and nonlinear systems of equations. When the time variation of the system can be modeled exactly by a polynomial it produces nearly exact solutions for a wide range of time step sizes. Solutions of a model nonlinear dynamic response exhibiting chaotic behavior have been computed. Accuracy of the method has been demonstrated by comparison with solutions obtained by established methods.

  8. QUANTIFYING THE CHALLENGES OF DETECTING UNSEEN PLANETARY COMPANIONS WITH TRANSIT TIMING VARIATIONS

    SciTech Connect

    Veras, Dimitri; Ford, Eric B.; Payne, Matthew J.

    2011-02-01

    Both ground- and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. The variation in a planet's transit times may be used to infer the presence of additional planets. Deducing the masses and orbital parameters of such planets from transit time variations (TTVs) alone is a rich and increasingly relevant dynamical problem. In this work, we evaluate the extent of the degeneracies in this process, systematically explore the dependence of TTV signals on several parameters, and provide phase space plots that could aid observers in planning future observations. Our explorations are focused on a likely-to-be prevalent situation: a known transiting short-period Neptune- or Jupiter-sized planet and a suspected external low-mass perturber on a nearly coplanar orbit. Through {approx}10{sup 7} N-body simulations, we demonstrate how TTV signal amplitudes may vary by orders of magnitude due to slight variations in any one orbital parameter (10{sup -3} AU in a semimajor axis, 0.005 in eccentricity, or a few degrees in orbital angles), and quantify the number of consecutive transit observations necessary in order to obtain a reasonable opportunity of characterizing the unseen planet ({approx}>50 observations). Planets in or near period commensurabilities of the form p:q, where p {<=} 20 and q {<=} 3, produce distinct TTV signatures, regardless of whether the planets are actually locked in a mean motion resonance. We distinguish these systems from the secular systems in our explorations. Additionally, we find that computing the autocorrelation function of a TTV signal can provide a useful diagnostic for identifying possible orbits for additional planets and suggest that this method could aid integration of TTV signals in future studies of particular exosystems.

  9. Coronary arterial dynamics computation with medical-image-based time-dependent anatomical models and element-based zero-stress state estimates

    NASA Astrophysics Data System (ADS)

    Takizawa, Kenji; Torii, Ryo; Takagi, Hirokazu; Tezduyar, Tayfun E.; Xu, Xiao Y.

    2014-10-01

    We propose a method for coronary arterial dynamics computation with medical-image-based time-dependent anatomical models. The objective is to improve the computational analysis of coronary arteries for better understanding of the links between the atherosclerosis development and mechanical stimuli such as endothelial wall shear stress and structural stress in the arterial wall. The method has two components. The first one is element-based zero-stress (ZS) state estimation, which is an alternative to prestress calculation. The second one is a "mixed ZS state" approach, where the ZS states for different elements in the structural mechanics mesh are estimated with reference configurations based on medical images coming from different instants within the cardiac cycle. We demonstrate the robustness of the method in a patient-specific coronary arterial dynamics computation where the motion of a thin strip along the arterial surface and two cut surfaces at the arterial ends is specified to match the motion extracted from the medical images.

  10. Time-dependent Mott transition in the periodic Anderson model with nonlocal hybridization

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix; Potthoff, Michael

    2016-08-01

    The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard-U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap opens in the spectral function of the localized orbitals only. We discuss the dependence of the critical interaction and of the final-state effective temperature on the hybridization strength and point out the various similarities between the nonequilibrium and the equilibrium Mott transition. It is shown that these can also be smoothly connected to each other by increasing the duration of a U-ramp from a sudden quench to a quasi-static process. The physics found for the model with off-site hybridization is compared with the dynamical Mott transition in the single-orbital Hubbard model and with the dynamical crossover found for the real-time dynamics of the conventional Anderson lattice with on-site hybridization.