Evidence Of Turbulence Research Articles

Nocturnal Turbulence at Jezero Crater as Determined From MEDA Measurements and Modeling

AbstractMars 2020 Mars Environmental Dynamics Analyzer (MEDA) instrument data acquired during half of a Martian year (Ls 13°–180°), and modeling efforts with the Mars Regional Atmospheric Modeling System (MRAMS) and the Mars Climate Database (MCD) enable the study of the seasonal evolution and variability of nocturnal atmospheric turbulence at Jezero crater. Nighttime conditions in Mars's Planetary Boundary Layer are highly stable because of strong radiative cooling that efficiently inhibits convection. However, MEDA nighttime observations of simultaneous rapid fluctuations in horizontal wind speed and air temperatures suggest the development of nighttime turbulence in Jezero crater. Mesoscale modeling with MRAMS also shows a similar pattern and enables us to investigate the origins of this turbulence and the mechanisms at play. As opposed to Gale crater, less evidence of turbulence from breaking mountain wave activity was found in Jezero during the period studied with MRAMS. On the contrary, the model suggests that nighttime turbulence at Jezero crater is explained by increasingly strong wind shear produced by the development of an atmospheric bore‐like disturbance at the nocturnal inversion interface. These atmospheric bores are produced by downslope winds from the west rim undercutting a strong low‐level jet aloft from ∼19:00 to 01:00 LTST and from ∼01:00 LTST to dawn when undercutting weak winds aloft. The enhanced wind shear leads to a reduction in the Richardson number and an onset of mechanical turbulence. Once the critical Richardson Number is reached (Ri ∼ <0.25), shear instabilities can mix warmer air aloft down to the surface.

An overview of participation in NASA’s CarpetDIEM campaign

This talk summarizes Brigham Young University’s (BYU) participation in NASA’s 2019 sonic boom data collection campaign in California, USA. Dubbed “Carpet Determination In Entirety Measurement” (CarpetDIEM) Phase I, the program was designed to measure conventional cruise booms across a widespread time-synchronous array, at the site where initial acoustical testing of the X-59 low-boom supersonic aircraft is planned. BYU deployed a total of 11 portable data acquisition systems across 10 nautical miles and tested a variety of microphone and data acquisition configurations. This talk describes both technical and logistical lessons learned at CarpetDIEM Phase I that can help with future X-59 test design including acquisition hardware comparison and evidence of turbulence. [Work supported by NASA Langley Research Center through the National Institute of Aerospace.]

Recursive Cointegration Analysis of Purchasing Power Parity: An Application to Asian Countries

Previous studies have utilized conventional cointegration tests that are based on the assumption that the long-run purchasing power parity (PPP) relationship is stable over the sample period. This assumption can be misleading if there were significant economic and policy changes over the sample period. To allow for the possibility of instability in the long-run PPP relationship, we utilize recursive cointegration analysis to test for the stability of cointegrating ranks and parameters. The results indicate evidence of cointegration for Korea, Malaysia, and Singapore, and a short window for Thailand around the 1997/98 Asian crisis with no evidence of structural breaks in the cointegrating vectors. Evidence of turbulence is detected around the 1997/98 crisis, the 1985 Plaza Accord, and around 1978-1984. Longrun parameters appear to have been stable for Malaysia, the Philippines, and Singapore, whereas instable for Indonesia, Korea, and Thailand.

Investigation of flux turbulence in iron-based superconductors

We explore the magnetic flux penetration in single crystals of the 122-type iron-based superconductors after remagnetization using magneto-optical imaging. We find evidence for turbulence at the boundary between vortices and antivortices. The turbulenceis characterized by increased fingering of the flux front.Moreover, steps in local magnetic induction are observed at the flux boundary. Our results show that flux turbulence is observed even for low-anisotropy type-II superconductors and is not confined to the cuprates.

The Turbopause experiment: atmospheric stability and turbulent structure spanning the turbopause altitude

Abstract. Very few sequences of high resolution wind and temperature measurements in the lower thermosphere are available in the literature, which makes it difficult to verify the simulation results of models that would provide better understanding of the complex dynamics of the region. To address this problem the Turbopause experiment used four rockets launched over a period of approximately two hours from Poker Flat Research Range, Alaska (64° N, 147° W) on the night of 17–18 February 2009. All four rocket payloads released trimethyl aluminum trails for neutral wind and turbulence measurements, and two of the rockets carried ionization gauges and fixed-bias Langmuir probes measuring neutral and electron densities, small-scale fluctuations and neutral temperatures. Two lidars monitored temperature structure and sodium densities. The observations were made under quiet geomagnetic conditions and show persistence in the wind magnitudes and shears throughout the observing period while being modulated by inertia-gravity waves. High resolution temperature profiles show the winter polar mesosphere and lower thermosphere in a state of relatively low stability with several quasi-adiabatic layers between 74 and 103 km. Temperature and wind data were combined to calculate Richardson number profiles. Evidence for turbulence comes from simultaneous observations of density fluctuations and downward transport of sodium in a mixed layer near 75 km; the observation of turbulent fluctuations and energy dissipation from 87–90 km; and fast and irregular trail expansion at 90–93 km, and especially between 95 to 103 km. The regions of turbulent trails agree well with regions of quasi-adiabatic temperature gradients. Above 103 km, trail diffusion was mainly laminar; however, unusual features and vortices in the trail diffusion were observed up to 118 km that have not been as prevalent or as clearly evident in earlier trail releases.

Transitional Flow and Related Transport Phenomena in Curved Microchannels

In microchannels with typical dimensions from 10 μm to a few hundreds of micrometers, the flow is dominated by viscous forces, often leading to laminar flow conditions. At the entrance or in bends and curves, where the flow changes its velocity or direction, inertial forces generate transverse flow velocities. Due to continuity, vortex pairs, such as Dean flow in circular bends, are generated, which are still laminar, steady, and showing no statistically distributed fluctuations typical for turbulent flow. This deviation from straight laminar conditions is called transitional flow, often occurring in channels larger than 500 μm at higher flow rates. Transitional flow phenomena include the first occurrence of flow bifurcation, pulsating vortices, period doubling of vortex pairs, and regularly fluctuating wake flow or vortex shedding. Chaotic flow phenomena are the first evidence of turbulence. Transitional flow augments the transport characteristics in microchannels for enhanced heat and mass transfer and for performing chemical reactions in microreactors. The profound understanding of how to generate and control vortices in microchannels guides the design of advanced microstructured devices for various applications.

Transabdominal two‐ and three‐dimensional color Doppler imaging of a uterine arteriovenous malformation

Uterine arteriovenous malformation (AVM) is a rare condition that has been reported in patients ranging in age between 18 and 72 years1. Several terms have been used for uterine AVM, including arteriovenous fistula, arteriovenous aneurysm, cirsoid aneurysm, racemose aneurysm, pulsatile angioma and cavernous angioma2. Arteriovenous malformations can be congenital or acquired and consist of a ‘proliferation of arterial and venous channels with fistula formation and an admixture of small capillary-like channels’2. Congenital AVM is very rare and is the result of a defect in the embryonic development of vascular structures3,4. Most uterine AVMs are acquired following damage to the uterine tissue. Cases of acquired AVM have been attributed to a variety of causes, including pelvic trauma, surgical interventions such as dilatation and curettage and Cesarean section, cervical and endometrial carcinoma, trophoblastic diseases, inflammation and diethylstilbestrol exposure, and can be idiopathic5–8. Uterine AVMs grow slowly and the appearance of symptoms may be delayed. However, the onset of symptoms can be sudden4. Patients may suffer from irregular vaginal bleeding, heavy menses and/or abdominal pain. Bleeding is thought to occur as a result of vessels of the AVM being exposed by shedding of the endometrium. There are several signs that can indicate the diagnosis of uterine AVM; an audible bruit or palpable thrill may be present and in some cases a pulsatile mass can be detected on manual examination7. A 40-year-old woman (gravida 6, para 3, abortus 3) presented at our hospital with heavy menstrual bleeding. The bleeding was reduced by intravenous administration of 10 IU oxytocin in physiological solution and methylergonovine maleate was then prescribed until bleeding ceased. An ultrasound scan was performed 3 days after this. The patient declined to undergo a transvaginal scan. On transabdominal gray-scale ultrasound, we observed multiple irregular hypoechoic spaces in the anterior wall and fundus of the uterus, which formed a mass that extended to the endometrium Figure 1 Gray-scale transabdominal ultrasound image showing hypoechoic spaces in the anterior wall and fundal part of the uterus extending to the endometrium.

Evidence of turbulence in laser-induced plasmas

By focusing a pulsed single mode Nd:YAG laser, we created low temperature plasmas at various pressures with various target gases and collected spectral light emissions to investigate the possibility of turbulent behavior in these types of plasmas. Characteristic fluctuation frequencies, chaotic dimensions, spectral indices, and turbulent fluctuation energies are determined from fluctuations in these spectral light emissions. Values calculated for the spectral index and the chaotic index for each plasma event are found to be within the known values for other turbulent plasma systems. Thus, turbulent fluctuations on a nanosecond time scale are confirmed in the time evolutions of various singly ionized and neutral spectral lines of various gases.

Comparison of Magnetic Field Structures on Different Scales in and around the Filamentary Dark Cloud GF 9

New visible polarization data combined with existing IR and FIR polarization data are used to study how the magnetic field threading the filamentary molecular cloud GF 9 connects to larger structures in its general environment. We find that when both visible and NIR polarization data are plotted as a function of extinction, there is no evidence for a plateau or a saturation effect in the polarization at Av ~ 1.3 as seen in dark clouds in Taurus. This lack of saturation effect suggests that even in the denser parts of GF 9 we are still probing the magnetic field. The visible polarization is smooth and has a well-defined orientation. The IR data are also well defined but with a different direction, and the FIR data in the core region are well defined and with yet another direction, but are randomly distributed in the filament region. On the scale of a few times the mean radial dimension of the molecular cloud, it is as if the magnetic field were `blind' to the spatial distribution of the filaments while on smaller scales within the cloud, in the core region near the IRAS point source PSC 20503+6006, polarimetry shows a rotation of the magnetic field lines in these denser phases. Hence, in spite of the fact that the spatial resolution is not the same in the visible/NIR and in the FIR data, all the data put together indicate that the field direction changes with the spatial scale. Finally, the Chandrasekhar and Fermi method is used to evaluate the magnetic field strength, indicating that the core region is approximately magnetically critical. A global interpretation of the results is that in the core region an original poloidal field could have been twisted by a rotating elongated (core+envelope) structure. There is no evidence for turbulence and ambipolar diffusion does not seem to be effective at the present time.

Turbulence measurements and implications for gravity wave dissipation during the MaCWAVE/MIDAS rocket program

Three altitude profiles of turbulent energy dissipation rates measured during the MaCWAVE/MIDAS summer rocket program are presented. All measurements show near continuous turbulent layers from ∼72–90 km altitude. Above 82 km altitude measured dissipation rates are comparable to former results. Below 82 km the MaCWAVE/MIDAS measurements provide the first evidence for turbulence in summer at these altitudes ever obtained. This unusual turbulence activity is accompanied by a reduced altitude of the zonal wind maximum, colder temperatures below 85 km, and enhanced gravity wave amplitudes above ∼75 km. The larger gravity wave amplitudes can be explained by the different local thermal structure through the wave amplitude dependence on the buoyancy frequency. These larger wave amplitudes lead to wave breaking, turbulence production, and forcing of the zonal wind at lower altitudes. Our measurements hence imply that the altitude of the zonal wind maximum is a sensitive indicator for the altitude distribution of turbulence in the upper mesosphere.

Influence of Dispersed Particulates on Mass Transport in Cross-Corrugated Structures

A study of the effect of particulate solids on mass transport behaviour in cross-corrugated membrane systems is reported. The electrochemical limiting current technique was employed to determine the mass transfer coefficients. The influence of cross-corrugated structures, to simulate membranes, and the effect of the orientation of flow to the angle of corrugation (0°, 45° and 90°) on the mass transfer coefficient is reported. The effect of particulate solids on mass transport was investigated using SiO2, at concentrations of up to 0.2 wt %. The presence of SiO2, at a concentration lower than 0.2%, gave higher values of mass transfer coefficient compared to those in the absence of the solid. The mass transport correlations showed that even at low values of Reynolds number there is evidence of turbulence.

Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

We report on the detection and analysis of hot ro-vibrational H2O emission from SVS-13, a young stellar object previously known to have strong CO overtone bandhead emission. Modeling of the high-resolution infrared spectrum shows that the H2O emission is characterized by temperatures ~ 1500 K, significantly lower than the temperatures that characterize the CO bandhead emission. The widths for the H2O lines are also found to be smaller than those for the CO lines. We construct a disk model for the emission that reproduces the CO and H2O spectrum. In this model, the H2O lines originate at somewhat larger disk radii (<= 0.3 AU) than the CO overtone lines (<= 0.1 AU). We find that the H2O abundance is about a factor of 10 lower than the calculated chemical equilibrium abundance. Large, approximately transonic, local line broadening is required to fit the profile of the CO bandhead. If this velocity dispersion is identified with turbulence, it is of significant interest regarding the transport of angular momentum in disks. Large local broadening is also required in modeling CO overtone emission from other young stellar objects, suggesting that large turbulent velocities may be characteristic of the upper atmospheres of the inner disks of young stars.

Three‐dimensional particle simulations of collisionless magnetic reconnection

Three‐dimensional (3‐D) particle simulations are performed in a double current layer configuration to investigate the stability of current sheets and boundary layers which develop during magnetic reconnection of antiparallel fields in collisionless plasma. The strong current layers that develop near the x line remain surprisingly laminar, with no evidence of turbulence and associated anomalous resistivity or viscosity. Neither the electron shear flow instabilities nor kink‐like instabilities, which have been observed in these current layers in earlier simulations, are present. The sharp boundary layers which form between the inflow and outflow regions downstream of the x line are unstable to the lower hybrid drift instability. The associated fluctuations, however, do not strongly impact the rate of reconnection. As a consequence, magnetic reconnection in the 3‐D system remains nearly two dimensional.

Color duplex ultrasonography of the superior mesenteric artery after placement of endografts with suprarenal stents.

After endovascular repair of abdominal aortic aneurysm with endografts with suprarenal stents, the proximal uncovered stent may cross the origin of the superior mesenteric artery. Effects on splanchnic circulation are unknown and may include development of stenosis at the vicinity of the stent. The criteria of high-grade superior mesenteric artery stenosis using color duplex ultrasonography have been previously reported. The purpose of this study is to examine the incidence of high-grade superior mesenteric artery stenosis in patients with endografts with suprarenal stents using color duplex ultrasonography. Candidates for the study were patients who had placement of an aortic endograft with a suprarenal stent and were able to undergo ultrasonography of the superior mesenteric artery. After reviewing computed tomography scans, patients who had the origin of the superior mesenteric artery crossed by the suprarenal stent underwent color duplex ultrasonography of this vessel. Presence of turbulence or narrowing of the superior mesenteric artery, or a peak systolic velocity greater than 2.75 m/sec, or an end-diastolic velocity greater than 0.45 m/sec were considered significant for the presence of high-grade superior mesenteric artery stenosis. There were 24 patients (21 males, three females), median age 71 years (range, 59-83). The suprarenal stent was crossing the superior mesenteric artery in 17 of 24 patients (71%). Color duplex ultrasound was technically successful in 13 of 17 (76%). The test was performed after a median follow-up of 9 months (range, 3 days to 34 months). No patient had evidence of turbulence or narrowing of the superior mesenteric artery during ultrasonography. The median peak systolic velocity was 0.92 m/sec (range, 0.53-1.21 m/sec). No patient had peak systolic velocity greater than 2.75 m/sec. The median end-diastolic velocity was 0.10 m/sec (range, 0.09-0.14 m/sec). No patient had end-diastolic velocity greater than 0.45 m/sec. Color duplex ultrasonography did not demonstrate the presence of high-grade superior mesenteric artery stenosis during early follow-up of patients with endografts with suprarenal stents. Longer follow-up of larger series of patients is needed to determine the long-term effects of suprarenal stents on splanchnic circulation.

Rapid Profile Variations in the Broad Hα Line of the Seyfert Galaxy Markarian 6: Possible Evidence for Turbulence in the Accretion Disk

We report on implications for the geometrical and kinematic parameters of BLR gas on the basis of short timescale variability in the broad Hα profile shape. Data on rapid variations have been obtained at the 2.6−m telescope of the BAO (Asatrian, Khachikian &amp; Notni, 1999). To search for variations in the profile, difference spectra (second minus first epoch) were examined. We believe that the structure of the underlying stellar continuum and the atmospheric features do not affect significantly the Hα difference profiles of Mark 6. Variations occurred simultaneously on the blue and red sides of Hα on a time scale of ≃ 50.7 minutes and take the form of three narrow, positive small bumps on each side in the difference spectrum. The positions of the bumps are −4400, −3100, −1700 and +1900, +4200 and +6600 kms−1. These changes may indicate the response of circularly rotating emitting gas at three orbits to a light pulse from a central source. In this case the pairs of blue and red bumps observed at −4400 and +6600, −3100 and +4200, and −1700 and 1900 km s−1 are formed in two opposite zones of gas close to the line of nodes. On the assumption that these orbits lie around a central massive object, orbital parameters (radii, velocities and inclination angles of orbital planes) of the clouds and the central mass can be found. The shift of each bump is defined by the combination of the relativistic Doppler effect due to the Keplerian orbital motion and the gravitational redshift. The six observed radial velocities are determined by six parameters: the orbital radii, R1, R2, R3 (or velocities, Vi, V2, V3) and the inclination angles i1, i2, i3 of the rotation planes. Thus, the expressions for the radial velocities form a system of six algebraic equations with six unknowns and can be solved. Using the difference of the orbital radii in absolute units (R3 − R1 = Δt C, where ΔtC, ≃ 50.7 minutes and C is the speed of light) we can derive the central mass M. Analytical solution gives: Error limits for the results are determined by the uncertainty of the input radial velocities, 300 km s−1. However, the value of the mass obtained is smaller by two orders of magnitude than the estimate for the dynamical mass of the nucleus of Mark 6 (M = 1 × 107M⊙ Dibai 1984). Such a low mass is excluded, therefore.

Rapid Variations in the Broad Hβ Profile of the Radio Galaxy 3C 390.3: Possible Evidence for Turbulence in the Accretion Disk

We report on implications for the geometrical and kinematic parameters of BLR gas on the basis of short timescale variability in the broad Hβ profile.Data on rapid variations have been obtained at the 6-m telescope of the SAO (Asatrian, Khachikian &amp; Notni, 1999). To search for variations in the profile shape, difference spectra (first minus second epoch) were examined. We believe that the structure of the underlying stellar continuum and the atmospheric features do not affect the Hβ difference profiles of 3C 390.3 significantly.Variations occurred simultaneously on the blue and red sides of Hβ on a timescale of ~ 1.452 hours and take the form of three narrow, positive and negative small bumps drifting across the line profile in the difference spectrum. The positions of the bumps are −2300, +4700 (negative) and −3700 kms2212;1 (positive).

An in vitro comparison of the hemodynamics of two inferior vena cava filters

Purpose: The effectiveness of an inferior vena cava (IVC) filter in preventing pulmonary embolism while preserving caval flow is significantly affected by its hemodynamic characteristics. Flow fields surrounding two types of IVC filters were compared to assess how the design of a filter may influence performance.Methods: The 12F Titanium Greenfield and VenaTech LGM inferior vena cava filters were studied in vitro with a noninvasive flow visualization technique, the photochromic flow visualization and measurement technique. Axial velocity profiles and wall shear stress distributions were measured. These results were compared with analytical data corresponding to the flow field in the absence of a filter to determine the relative extent of the flow disturbances.Results: The reductions in near-wall axial velocity and wall shear stress caused by the VenaTech filter were more extensive and severe than those caused by the Greenfield filter. These changes were the consequence of differences in the geometry and dimensions of the struts of the two filters. The measurements showed the flow fields to be laminar, with no evidence of turbulence in both cases.Conclusion: Two factors that have been linked to thrombogenesis, near-wall velocity and wall-shear stress, were significantly affected by the larger frontal profile area of the VenaTech filter. Although a larger area may increase clot-trapping efficiency, as shown by previous studies, the reduced near-wall velocities and wall shear stresses may increase the potential for thrombogenesis and, thus, caval occlusion. In contrast to other in vitro flow visualization studies, no turbulence was observed with either filter.

An in vitro comparison of the hemodynamics of two inferior vena cava filters

The effectiveness of an inferior vena cava (IVC) filter in preventing pulmonary embolism while preserving caval flow is significantly affected by its hemodynamic characteristics. Flow fields surrounding two types of IVC filters were compared to assess how the design of a filter may influence performance. The 12F Titanium Greenfield and VenaTech LGM inferior vena cava filters were studied in vitro with a noninvasive flow visualization technique, the photochromic flow visualization and measurement technique. Axial velocity profiles and wall shear stress distributions were measured. These results were compared with analytical data corresponding to the flow field in the absence of a filter to determine the relative extent of the flow disturbances. The reductions in near-wall axial velocity and wall shear stress caused by the VenaTech filter were more extensive and severe than those caused by the Greenfield filter. These changes were the consequence of differences in the geometry and dimensions of the struts of the two filters. The measurements showed the flow fields to be laminar, with no evidence of turbulence in both cases. Two factors that have been linked to thrombogenesis, near-wall velocity and wall-shear stress, were significantly affected by the larger frontal profile area of the VenaTech filter. Although a larger area may increase clot-trapping efficiency, as shown by previous studies, the reduced near-wall velocities and wall shear stresses may increase the potential for thrombogenesis and, thus, caval occlusion. In contrast to other in vitro flow visualization studies, no turbulence was observed with either filter.

The Advertising Industry in a Turbulent Environment: A Research Agenda and Call for Action

Abstract The advertising industry is facing difficult times. Although some of the difficulties are related to business cycles, there is evidence of turbulence in the advertising industry. The advertising industry should investigate possible causes of this turbulence and develop counterturbulent strategies. Research questions are posited in this article, hypotheses are formulated, and a call for action is made.

Fractal Properties of Extragalactic Jets: Evidence of Turbulence?

Several different properties of extragalactic radio sources have been attributed to the effects of turbulence. The morphological appearance of FRI sources has been often interpreted as the result of turbulent entrainment in subsonic or transonic flows (Bicknell 1984, 1986). Moreover, particle acceleration by MHD turbulence via a second order Fermi process is one of the possible ways for accelerating the synchrotron emitting relativistic particles (see Ferrari, Trussoni &amp; Zaninetti 1979). Turbulence appears therefore as an important ingredient in the theoretical modelling of extragalactic radio sources; however, we do not have, unfortunately, any direct evidence of it.