74 research outputs found
Multifluid magnetohydrodynamic turbulent decay
It is generally believed that turbulence has a significant impact on the
dynamics and evolution of molecular clouds and the star formation which occurs
within them. Non-ideal magnetohydrodynamic effects are known to influence the
nature of this turbulence. We present the results of a suite of 512-cubed
resolution simulations of the decay of initially super-Alfvenic and supersonic
fully multifluid MHD turbulence. We find that ambipolar diffusion increases the
rate of decay of the turbulence while the Hall effect has virtually no impact.
The decay of the kinetic energy can be fitted as a power-law in time and the
exponent is found to be -1.34 for fully multifluid MHD turbulence. The power
spectra of density, velocity and magnetic field are all steepened significantly
by the inclusion of non-ideal terms. The dominant reason for this steepening is
ambipolar diffusion with the Hall effect again playing a minimal role except at
short length scales where it creates extra structure in the magnetic field.
Interestingly we find that, at least at these resolutions, the majority of the
physics of multifluid turbulence can be captured by simply introducing fixed
(in time and space) resistive terms into the induction equation without the
need for a full multifluid MHD treatment. The velocity dispersion is also
examined and, in common with previously published results, it is found not to
be power-law in nature.Comment: 16 pages, 15 figures, Accepted for publication in Ap
Spectral Properties of Compressible Magnetohydrodynamic Turbulence from Numerical Simulations
We analyze the spectral properties of driven, supersonic compressible
magnetohydrodynamic (MHD) turbulence obtained via high-resolution numerical
experiments, for application to understanding the dynamics of giant molecular
clouds. Via angle-averaged power spectra, we characterize the transfer of
energy from the intermediate, driving scales down to smaller dissipative
scales, and also present evidence for inverse cascades that achieve
modal-equipartition levels on larger spatial scales. Investigating compressive
versus shear modes separately, we evaluate their relative total power, and find
that as the magnetic field strength decreases, (1) the shear fraction of the
total kinetic power decreases, and (2) slopes of power-law fits over the
inertial range steepen. To relate to previous work on incompressible MHD
turbulence, we present qualitative and quantitative measures of the
scale-dependent spectral anisotropy arising from the shear-Alfv\'{e}n cascade,
and show how these vary with changing mean magnetic field strength. Finally, we
propose a method for using anisotropy in velocity centroid maps as a diagnostic
of the mean magnetic field strength in observed cloud cores.Comment: 22 pages, 11 figures; Ap.J., accepte
Antitumor Mechanisms of Lycium barbarum Fruit: An Overview of In Vitro and In Vivo Potential
Lycium barbarum, known as goji berry or wolfberry, is a fruit long associated with health
benefits, showing a plethora of effects ranging from antioxidant, anticancer, anti-inflammatory, and
immunomodulatory effects. Its potential is attributed to the significant presence of polysaccharides, glycopeptides, polyphenols, flavonoids, carotenoids, and their derivatives. These compounds effectively ounteract the action of free radicals, positively influencing cellular balance and intracellular
signaling, contributing to overall cell health and function acting on multiple molecular pathways. Several fractions extracted from goji berries demonstrate antitumor properties, particularly effective
against breast cancer, without showing cytotoxic effects on normal human cells. Hence, the review
explored the fundamental traits of bioactive elements in Lycium barbarum and their potential in cancer
treatment and, specifically, breast cancer. It focused on elucidating wolfberryâs influenced biochemical
pathways, its synergism with anticancer drugs, and its potential to alleviate the side effects associated
with existing cancer treatments
Numerical Simulations of Driven Relativistic MHD Turbulence
A wide variety of astrophysical phenomena involve the flow of turbulent
magnetized gas with relativistic velocity or energy density. Examples include
gamma-ray bursts, active galactic nuclei, pulsars, magnetars, micro-quasars,
merging neutron stars, X-ray binaries, some supernovae, and the early universe.
In order to elucidate the basic properties of the relativistic
magnetohydrodynamical (RMHD) turbulence present in these systems, we present
results from numerical simulations of fully developed driven turbulence in a
relativistically warm, weakly magnetized and mildly compressible ideal fluid.
We have evolved the RMHD equations for many dynamical times on a uniform grid
with 1024^3 zones using a high order Godunov code. We observe the growth of
magnetic energy from a seed field through saturation at about 1% of the total
fluid energy. We compute the power spectrum of velocity and density-weighted
velocity and conclude that the inertial scaling is consistent with a slope of
-5/3. We compute the longitudinal and transverse velocity structure functions
of order p up to 11, and discuss their possible deviation from the expected
scaling for non-relativistic media. We also compute the scale-dependent
distortion of coherent velocity structures with respect to the local magnetic
field, finding a weaker scale dependence than is expected for incompressible
non-relativistic flows with a strong mean field.Comment: Accepted to Ap
On the role of stochastic Fermi acceleration in setting the dissipation scale of turbulence in the interstellar medium
We consider the dissipation by Fermi acceleration of magnetosonic turbulence
in the Reynolds Layer of the interstellar medium. The scale in the cascade at
which electron acceleration via stochastic Fermi acceleration (STFA) becomes
comparable to further cascade of the turbulence defines the inner scale. For
any magnetic turbulent spectra equal to or shallower than Goldreich-Sridhar
this turns out to be cm, which is much larger than the shortest
length scales observed in radio scintillation measurements. While STFA for such
spectra then contradict models of scintillation which appeal directly to an
extended, continuous turbulent cascade, such a separation of scales is
consistent with the recent work of \citet{Boldyrev2} and \citet{Boldyrev3}
suggesting that interstellar scintillation may result from the passage of radio
waves through the galactic distribution of thin ionized boundary surfaces of
HII regions, rather than density variations from cascading turbulence. The
presence of STFA dissipation also provides a mechanism for the non-ionizing
heat source observed in the Reynolds Layer of the interstellar medium
\citep{Reynolds}. STFA accommodates the proper heating power, and the input
energy is rapidly thermalized within the low density Reynolds layer plasma.Comment: 12 Pages, no figures. Accepted for publication in MNRA
Cascade and Damping of Alfv\'{e}n-Cyclotron Fluctuations: Application to Solar Wind Turbulence Spectrum
With the diffusion approximation, we study the cascade and damping of
Alfv\'{e}n-cyclotron fluctuations in solar plasmas numerically. Motivated by
wave-wave couplings and nonlinear effects, we test several forms of the
diffusion tensor. For a general locally anisotropic and inhomogeneous diffusion
tensor in the wave vector space, the turbulence spectrum in the inertial range
can be fitted with power-laws with the power-law index varying with the wave
propagation direction. For several locally isotropic but inhomogeneous
diffusion coefficients, the steady-state turbulence spectra are nearly
isotropic in the absence of damping and can be fitted by a single power-law
function. However, the energy flux is strongly polarized due to the
inhomogeneity that leads to an anisotropic cascade. Including the anisotropic
thermal damping, the turbulence spectrum cuts off at the wave numbers, where
the damping rates become comparable to the cascade rates. The combined
anisotropic effects of cascade and damping make this cutoff wave number
dependent on the wave propagation direction, and the propagation direction
integrated turbulence spectrum resembles a broken power-law, which cuts off at
the maximum of the cutoff wave numbers or the He cyclotron frequency.
Taking into account the Doppler effects, the model can naturally reproduce the
broken power-law wave spectra observed in the solar wind and predicts that a
higher break frequency is aways accompanied with a greater spectral index
change that may be caused by the increase of the Alfv\'{e}n Mach number, the
reciprocal of the plasma beta, and/or the angle between the solar wind velocity
and the mean magnetic field. These predictions can be tested by future
observations
Density Probability Distribution Functions in Supersonic Hydrodynamic and MHD Turbulence
We study the probability distribution function (PDF) of the mass density in
simulations of supersonic turbulence with properties appropriate for molecular
clouds. For this study we use Athena, a new higher-order Godunov code. We find
there are surprisingly similar relationships between the mean of the
time-averaged PDF and the turbulent Mach number for driven hydrodynamic and
strong-field MHD turbulence. There is, however, a large scatter about these
relations, indicating a high level of temporal and spatial variability in the
PDF. Thus, the PDF of the mass density is unlikely to be a good measure of
magnetic field strength. We also find the PDF of decaying MHD turbulence
deviates from the mean-Mach relation found in the driven case. This implies
that the instantaneous Mach number alone is not enough to determine the
statistical properties of turbulence that is out of equilibrium. The scatter
about the mean-Mach relation for driven turbulence, along with the large
departure of decaying turbulence PDFs from those of driven turbulence, may
illuminate one factor contributing to the large observed cloud-to-cloud
variation in the star formation rate per solar mass.Comment: 4 pages, 2 figures, published in ApJL; corrected sign in eqn. (4
A method for reconstructing the variance of a 3D physical field from 2D observations: Application to turbulence in the ISM
We introduce and test an expression for calculating the variance of a
physical field in three dimensions using only information contained in the
two-dimensional projection of the field. The method is general but assumes
statistical isotropy. To test the method we apply it to numerical simulations
of hydrodynamic and magnetohydrodynamic turbulence in molecular clouds, and
demonstrate that it can recover the 3D normalised density variance with ~10%
accuracy if the assumption of isotropy is valid. We show that the assumption of
isotropy breaks down at low sonic Mach number if the turbulence is
sub-Alfvenic. Theoretical predictions suggest that the 3D density variance
should increase proportionally to the square of the Mach number of the
turbulence. Application of our method will allow this prediction to be tested
observationally and therefore constrain a large body of analytic models of star
formation that rely on it.Comment: 8 pages, 9 figures, accepted for publication in MNRA
Potential Role of Natural Antioxidant Products in Oncological Diseases
Nutrition has a significant effect and a crucial role in disease prevention. Low consumption
of fruit and vegetables and a sedentary lifestyle are closely related with the onset and development of many types of cancer. Recently, nutraceuticals have gained much attention in cancer research due to their pleiotropic effects and relatively non-toxic behavior. In fact, although in the past there
have been conflicting results on the role of some antioxidant compounds as allies against cancer,
numerous recent clinical studies highlight the efficacy of dietary phytochemicals in the prevention and treatment of cancer. However, further investigation is necessary to gain a deeper understanding of the potential anticancer capacities of dietary phytochemicals as well as the mechanisms of their
action. Therefore, this review examined the current literature on the key properties of the bioactive
components present in the diet, such as carotenoids, polyphenols, and antioxidant compounds, as
well as their use in cancer therapy. The review focused on potential chemopreventive properties,
evaluating their synergistic effects with anticancer drugs and, consequently, the side effects associated
with current cancer treatments
Anticancer Therapies Based on Oxidative Damage: Lycium barbarum Inhibits the Proliferation of MCF-7 Cells by Activating Pyroptosis through Endoplasmic Reticulum Stress
Abstract: Lycium barbarum, commonly recognized as goji berry or wolfberry, is highly appreciated
not only for its organoleptic and nutritional properties but also as an important source of bioactive
compounds such as polysaccharides, carotenoids, phenolics, and various other non-nutritive
compounds. These constituents give it a multitude of health benefits, including antioxidant, antiinflammatory,
and anticancer properties. However, the precise biochemical mechanisms responsible
for its anticancer effects remain unclear, and the comprehensive composition of goji berry extracts is
often insufficiently explored. This study aimed to investigate the biochemical pathways modulated
in breast cancer cells by an ethanolic extract of Lycium barbarum fruit (LBE). Following metabolomic
profiling using UHPLC-HRMS/MS, we assessed the antitumoral properties of LBE on different
breast cancer cell lines. This investigation revealed that LBE exhibited cytotoxic effects, inducing a
pro-oxidant effect that triggered pyroptosis activation through endoplasmic reticulum (ER) stress
and subsequent activation of the P-IRE1α/XBP1/NLRP3 axis in MCF-7 cells. In addition, LBE did
not display cytotoxicity toward healthy human cells but demonstrated antioxidant properties by
neutralizing ROS generated by doxorubicin. These findings underscore the potential of LBE as a
highly promising natural extract in cancer therap
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