5,498 research outputs found
Simultaneous interplanetary scintillation and Heliospheric Imager observations of a coronal mass ejection
No full textWe describe simultaneous Interplanetary Scintillation (IPS) and STEREO Heliospheric Imager (HI) observations of a coronal mass ejection (CME) on 16 May 2007. Strong CME signatures were present throughout the IPS observation. The IPS raypath lay within the field-of-view of HI-1 on STEREO-A and comparison of the observations shows that the IPS measurements came from a region within a faint CME front observed by HI-1A. This front may represent the merging of two converging CMEs. Plane-of-sky velocity estimates based on time-height plots of the two converging CME structures were 325 kms?1 and 550 kms?1 for the leading and trailing fronts respectively. The plane-of-sky velocities determined from IPS ranged from 420 ± 10 kms?1 to 520 ± 20 kms?1. IPS results reveal the presence of micro-structure within the CME front which may represent interaction between the two separate CME events. This is the first time that it has been possible to interpret IPS observations of small-scale structure within an interplanetary CME in terms of the global structure of the event
Rayleigh number dependence of the Archimedes number dependent large-scale flow structure formation in mixed convection
No full textWe report on experimental investigations of large-scale flow structure formation in mixed convection. We characterize the flow field by measuring the velocity fields within a rectangular model room using 2D2C PIV. The control parameters are the Reynolds number Re, the Rayleigh number Ra and the Prandtl number Pr. All parameters are linked through the Archimedes number Ar. In 6.4x10-2 ≤ Ar ≤ 1.39x101, 4.2x103 ≤ Re ≤ 6.35x104 and Ra = 3.1x107, Ra = 1.8x108 and Pr = 0.713 we found flow 3 different flow structures. While keeping Ra and Pr constant and varying Ar through Re variations, we found an Ar dependence of the largescale flow structure formation within 6.4x10-2 ≤ Ar ≤ 1.39x101. Furthermore, we found a Ra dependence of the structure formation, which shifts the transition points between the structures to higher Archimedes numbers and reduces the mean velocities within the investigated domain
Soil organic carbon dynamics of improved fallow-maize rotation systems under conventional and no-tillage in Central Zimbabwe
No full textFallowing increases soil organic carbon (SOC) during the fallowing phase. However, this benefit is lost quickly during the cropping phase. The objective of this study was to evaluate SOC dynamics of an improved fallow-maize rotation under no-tillage (NT) and conventional tillage (CT) from time of fallow termination, through the next two cropping seasons. The treatments studied were improved fallows of Acacia angustissima (A. angustissima) and Sesbania sesban (S. sesban), natural fallow and continuous maize. Our hypothesis is that fallowing maintained higher SOC and lower soil bulk densities through the cropping phase when compared with continuous maize system and that NT maintained higher SOC when compared with CT. Soil organic carbon was significantly greater under fallows than under continuous maize from fallow termination to the end of the second cropping season. Soil organic carbon for the 0¿5 cm depths was 11.0, 10.0, 9.4 and 6.6 g kg¿1 for A. angustissima, S. sesban, natural fallow and continuous maize, respectively at fallow termination. After two cropping seasons SOC for the same depth was 8.0, 7.0, 6.1, 5.9 g kg¿1 under CT and 9.1, 9.0, 8.0, 6.0 g kg¿1 under NT for A. angustissima, S. sesban, natural fallow and continuous maize, respectively. Total SOC stocks were also higher under fallows when compared with continuous maize at fallow termination and after two cropping seasons. Soil bulk densities were lower under fallows when compared with continuous maize during the period of study. We concluded that fallows maintained greater SOC and NT sequestered more SOC than CT. Acacia angustissima was the better tree legume fallow for SOC sequestration when compared with S. sesban or natural fallow because it maintained higher SOC and lower bulk densities after two seasons of maize cropping
Does diet play a role in the alleviation of rheumatoid arthritis symptoms?
No full textThis systematic review of scientific literature was undertaken to investigate the possibility of a role for diet in the alleviation of rheumatoid arthritis (RA) symptoms, with an objective of highlighting specific nutrients and/or certain food groups and diets that may impact upon the symptoms of RA. Studies displaying conflicting evidence (i.e. show diets that have no effect on RA symptom alleviation) were also reviewed. A comprehensive literature search to identify relevant papers was carried out with the use of criteria, in an attempt to identify as many studies as possible, but also to minimise selection bias for those that were found. Electronic databases, library catalogues and internet search engines played key parts in paper identification. A total of 31 papers were identified after meeting selection criteria and summaries and critical appraisals were compiled for comparison. Some studies show that fish oil supplementation displayed the greatest benefits through a reduction in the number of tender joints and morning stiffness. One paper offers a dosage figure for improvement in clinical symptoms as 40mg/kg body weight/day of oil containing n-3 fatty acids (FAs) combined with <10g/day of dietary (n-6) FAs. Periods of fasting with a vegetarian diet promotes a reduction in RA symptoms. Several studies identify Gammalinolenic Acid as capable of decreasing pro-inflammatory products of Arachidonic Acid. Similarly, elemental diets and foods devoid of allergens may benefit RA activity parameters, however improvements in RA symptoms seen in response to elemental diets are not sustained on individualised diets. Many researchers recognised the influence of a Mediterranean diet, rich in anti-oxidant containing vegetables, n-3 FAs and a lower ratio of n-6 to n-3 FAs as sources of inflammation reduction. Vitamin E treatment was shown to provide a small analgesic property compared to placebo, the mechanism of which and identification of additional vitamins and food sources with such potential require further study. Further work is required on establishing most beneficial supplement dosage, duration and length of treatment interval. Knowledge of correlations of food allergies in RA sufferers to immune responses compared to food antigens in the fluid of blood and joints would be useful
Reynolds numbers near the ultimate state of turbulent Rayleigh-Bénard convection
No full textWe report on measurements of the mean-flow Reynolds number ReU and the rms fluctuation Reynolds number ReV in turbulent Rayleigh-Bénard convection as a function of the Rayleigh number Ra for 4 x 1011 < Ra < 2 1014 and Pr ' 0:8. Both can be described by the same power law with an effective exponent = 0:44, in agreement with predictions for ReU but in disagreement with predictions for ReV
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
Lagrangian Raylaigh-Bénard convection
No full textUsing passive tracers as sensors, we obtain Lagrangian measurements of tracers position, velocity and temperature in Rayleigh-Bénard convection at Ra=10^7-10^9. We report on statistics of temperature, velocity, and heat transport (Nusselt number). We observe that the Nusselt number is characterized by a largely intermittent behavior, likely due to the interaction of temperature with turbulent velocity fluctuations
Photochemical behavior of some p-styryistilbenes and related compounds: Spectral properties and photoisomerization in solution and in solid state
No full textAuthor Posting. © The Authors (2006) This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in PHOTOCHEMISTRY AND PHOTOBIOLOGY, 82(6): 1645-1650. https://doi.org/10.1562/2006-01-17-RA-780ArticlePhotochemistry and Photobiology. 82(6): 1645-1650 (2006)journal articl
Aspect-ratio dependence of the transition to the ultimate state of turbulent Rayleigh-Bénard convection
No full textWe report on measurements of the ultimate-state transition in turbulent Rayleigh-B\'enard convection obtained in a large facility known as the ``Uboot of G\"ottingen" and using pressurized sulfur hexafluoride as the convecting fluid. We found that the transition occurs over a range of which becomes more narrow as increases, ranging from which is at most weakly dependent on and close to to which varies from about for to about for
Wall to wall optimal transport
No full textThe calculus of variations is employed to find steady divergence-free velocity fields that maximize transport of a tracer between two parallel walls held at fixed concentration for one of two constraints on flow strength: a fixed value of the kinetic energy or a fixed value of the enstrophy (the mean square rate of strain in this situation). The optimizing flows realize upper limits on convective transport in this scenario. We interpret the results in the context of buoyancy-driven Rayleigh–Bénard convection problems that satisfy the flow intensity constraints, enabling us to investigate how optimal transport scalings compare with upper bounds on Nu expressed as a function of the Rayleigh number Ra
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