854 research outputs found
Anomalously Weak Solar Convection
Convection in the solar interior is thought to comprise structures on a
spectrum of scales. This conclusion emerges from phenomenological studies and
numerical simulations, though neither covers the proper range of dynamical
parameters of solar convection. Here, we analyze observations of the wavefield
in the solar photosphere using techniques of time-distance helioseismology to
image flows in the solar interior. We downsample and synthesize 900 billion
wavefield observations to produce 3 billion cross-correlations, which we
average and fit, measuring 5 million wave travel times. Using these travel
times, we deduce the underlying flow systems and study their statistics to
bound convective velocity magnitudes in the solar interior, as a function of
depth and spherical-harmonic degree . Within the wavenumber band
, Convective velocities are 20-100 times weaker than current
theoretical estimates. This suggests the prevalence of a different paradigm of
turbulence from that predicted by existing models, prompting the question: what
mechanism transports the heat flux of a solar luminosity outwards? Advection is
dominated by Coriolis forces for wavenumbers , with Rossby numbers
smaller than at , suggesting that the Sun may be
a much faster rotator than previously thought, and that large-scale convection
may be quasi-geostrophic. The fact that iso-rotation contours in the Sun are
not co-aligned with the axis of rotation suggests the presence of a latitudinal
entropy gradient.Comment: PNAS; 5 figures, 5 page
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Sustainability Study in Selective Laser Sintering – An Energy Perspective
This paper presents a sustainability analysis of Selective Laser Sintering (SLS)
from an energy standpoint. Data of electrical power consumed by the system over an
entire build were acquired using a LabVIEW 8.6 circuit. The power drawn by individual
subsystems were also measured, and an energy balance was performed. These data were
then used to arrive at a Total Energy Indicator of the process with the help of a specific
type of Environmental and Resource Management Data (ERMD) known as Eco-Indicators, which indicates the level of sustainability of the process.Mechanical Engineerin
On the formation of cyclones and anticyclones in a rotating fluid
It is commonly observed that the columnar vortices that dominate the large scales in homogeneous, rapidly rotating turbulence are predominantly cyclonic. This has prompted us to ask how this asymmetry arises. To provide a partial answer to this we look at the process of columnar vortex formation in a rotating fluid and, in particular, we examine how a localized region of swirl (an eddy) can convert itself into a columnar structure by inertial wave propagation. We show that, when the Rossby number (Ro) is small, the vortices evolve into columnar eddies through the radiation of linear inertial waves. When the Rossby number is large, on the other hand, no such column is formed. Rather, the eddy bursts radially outward under the action of the centrifugal force. There is no asymmetry between cyclonic and anticyclonic eddies for these two regimes. However, cyclones and anticyclones behave differently in the intermediate regime of Ro~1. Here we find that the transition from columnar vortex formation to radial bursting occurs at lower values of Ro for anticyclones, with the transition for anticyclones occurring at Ro~0.5, and that for cyclones at Ro~2. Thus, in a homogeneous turbulence experiment conducted at, say, Ro=1, we would expect to see more cyclones than anticyclones. The reason for this asymmetry at Ro~1 is explained
Derivative moments in turbulent shear flows
We propose a generalized perspective on the behavior of high-order derivative
moments in turbulent shear flows by taking account of the roles of small-scale
intermittency and mean shear, in addition to the Reynolds number. Two
asymptotic regimes are discussed with respect to shear effects. By these means,
some existing disagreements on the Reynolds number dependence of derivative
moments can be explained. That odd-order moments of transverse velocity
derivatives tend not vanish as expected from elementary scaling considerations
does not necessarily imply that small-scale anisotropy persists at all Reynolds
numbers.Comment: 11 pages, 7 Postscript figure
Weak nuclear forces cause the strong nuclear force
We determine the strength of the weak nuclear force which holds the lattices
of the elementary particles together. We also determine the strength of the
strong nuclear force which emanates from the sides of the nuclear lattices. The
strong force is the sum of the unsaturated weak forces at the surface of the
nuclear lattices. The strong force is then about ten to the power of 6 times
stronger than the weak force between two lattice points.Comment: 12 pages, 1 figur
Beyond scaling and locality in turbulence
An analytic perturbation theory is suggested in order to find finite-size
corrections to the scaling power laws. In the frame of this theory it is shown
that the first order finite-size correction to the scaling power laws has
following form , where
is a finite-size scale (in particular for turbulence, it can be the Kolmogorov
dissipation scale). Using data of laboratory experiments and numerical
simulations it is shown shown that a degenerate case with can
describe turbulence statistics in the near-dissipation range , where
the ordinary (power-law) scaling does not apply. For moderate Reynolds numbers
the degenerate scaling range covers almost the entire range of scales of
velocity structure functions (the log-corrections apply to finite Reynolds
number). Interplay between local and non-local regimes has been considered as a
possible hydrodynamic mechanism providing the basis for the degenerate scaling
of structure functions and extended self-similarity. These results have been
also expanded on passive scalar mixing in turbulence. Overlapping phenomenon
between local and non-local regimes and a relation between position of maximum
of the generalized energy input rate and the actual crossover scale between
these regimes are briefly discussed.Comment: extended versio
A Minimalist Turbulent Boundary Layer Model
We introduce an elementary model of a turbulent boundary layer over a flat
surface, given as a vertical random distribution of spanwise Lamb-Oseen vortex
configurations placed over a non-slip boundary condition line. We are able to
reproduce several important features of realistic flows, such as the viscous
and logarithmic boundary sublayers, and the general behavior of the first
statistical moments (turbulent intensity, skewness and flatness) of the
streamwise velocity fluctuations. As an application, we advance some heuristic
considerations on the boundary layer underlying kinematics that could be
associated with the phenomenon of drag reduction by polymers, finding a
suggestive support from its experimental signatures.Comment: 5 pages, 10 figure
Antioxidant Activity and Hepatoprotective Potential of Polyalthia longifolia and Cassia spectabilis Leaves against Paracetamol-Induced Liver Injury
In the present study, in vitro antioxidant, free radical scavenging capacity, and hepatoprotective activity of methanol extracts from
Polyalthia longifolia and Cassia spectabilis were evaluated using established in vitro models such as ferric-reducing antioxidant
power (FRAP), 2,2-diphenyl-1-picryl-hydrazyl (DPPH•), hydroxyl radical (OH•), nitric oxide radical (NO•) scavenging, metal
chelating, and antilipidperoxidation activities. Interestingly, all the extracts showed considerable in vitro antioxidant and free
radical scavenging activities in a dose-dependent manner when compared to the standard antioxidant which verified the presence
of strong antioxidant compound in leaf extracts tested. Phenolic and flavonoid content of these extracts is significantly correlated
with antioxidant capacity. Since P. longifolia extract was exhibited better in vitro antioxidant activities, it was subjected for in
vivo hepatoprotective activity in paracetamol-intoxicated mice. Therapy of P. longifolia showed the liver protective effect on
biochemical and histopathological alterations. Moreover, histological studies also supported the biochemical finding, that is, the
maximum improvement in the histoarchitecture of the liver. Results revealed that P. longifolia leaf extract could protect the liver
against paracetamol-induced oxidative damage by possibly increasing the antioxidant protection mechanism inmice. Our findings
indicated that P. longifolia and C. spectabilis have potential as good sources of natural antioxidant/antiaging compounds
Asteroseismic detection of latitudinal differential rotation in 13 Sun-like stars
The differentially rotating outer layers of stars are thought to play a role
in driving their magnetic activity, but the underlying mechanisms that generate
and sustain differential rotation are poorly understood. We report the
measurement of latitudinal differential rotation in the convection zones of 40
Sun-like stars using asteroseismology. For the most significant detections, the
stars' equators rotate approximately twice as fast as their mid-latitudes. The
latitudinal shear inferred from asteroseismology is much larger than
predictions from numerical simulations.Comment: 45 pages, 11 figures, 4 tables, published in Scienc
Butterfly diagram of a Sun-like star observed using asteroseismology
Stellar magnetic fields are poorly understood but are known to be important
for stellar evolution and exoplanet habitability. They drive stellar activity,
which is the main observational constraint on theoretical models for magnetic
field generation and evolution. Starspots are the main manifestation of the
magnetic fields at the stellar surface. In this study we measure the variation
of their latitude with time, called a butterfly diagram in the solar case, for
the solar analogue HD 173701 (KIC 8006161). To that effect, we use Kepler data,
to combine starspot rotation rates at different epochs and the
asteroseismically determined latitudinal variation of the stellar rotation
rates. We observe a clear variation of the latitude of the starspots. It is the
first time such a diagram is constructed using asteroseismic data.Comment: 8 pages, 4 figures, accepted in A&A Letter
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