1,160 research outputs found
DNS of Laminar to Turbulent Transition on NACA 0012 Airfoil with Sand Grain Roughness
The Lattice-Boltzmann-based solver PowerFLOW is used to perform direct numerical simulations of the transitional flow over an airfoil at Reynolds number equal to 0.657 million. The leading edge of the airfoil is covered with sand particles, represented by polyhedra, to mimic the grit used in experiments. The sensitivity of the laminar to turbulent transition to the size of these particles, grid resolution, spanwise length is evaluated and rectangular trips are also tested
On the environment surrounding close-in exoplanets
Exoplanets in extremely close-in orbits are immersed in a local
interplanetary medium (i.e., the stellar wind) much denser than the local
conditions encountered around the solar system planets. The environment
surrounding these exoplanets also differs in terms of dynamics (slower stellar
winds, but higher Keplerian velocities) and ambient magnetic fields (likely
higher for host stars more active than the Sun). Here, we quantitatively
investigate the nature of the interplanetary media surrounding the hot Jupiters
HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the
three-dimensional winds of their host stars, in which we directly incorporate
their observed surface magnetic fields. With that, we derive mass-loss rates
(1.9 to 8.0 /yr) and the wind properties at the
position of the hot-Jupiters' orbits (temperature, velocity, magnetic field
intensity and pressure). We show that these exoplanets' orbits are
super-magnetosonic, indicating that bow shocks are formed surrounding these
planets. Assuming planetary magnetic fields similar to Jupiter's, we estimate
planetary magnetospheric sizes of 4.1 to 5.6 planetary radii. We also derive
the exoplanetary radio emission released in the dissipation of the stellar wind
energy. We find radio fluxes ranging from 0.02 to 0.13 mJy, which are
challenging to be observed with present-day technology, but could be detectable
with future higher sensitivity arrays (e.g., SKA). Radio emission from systems
having closer hot-Jupiters, such as from tau Boo b or HD189733b, or from nearby
planetary systems orbiting young stars, are likely to have higher radio fluxes,
presenting better prospects for detecting exoplanetary radio emission.Comment: 15 pages, 5 figures, accepted to MNRA
Long-term magnetic field stability of Vega
We present new spectropolarimetric observations of the normal A-type star
Vega, obtained during the summer of 2010 with NARVAL at T\'elescope Bernard
Lyot (Pic du Midi Observatory). This new time-series is constituted of 615
spectra collected over 6 different nights. We use the
Least-Square-Deconvolution technique to compute, from each spectrum, a mean
line profile with a signal-to-noise ratio close to 20,000. After averaging all
615 polarized observations, we detect a circularly polarized Zeeman signature
consistent in shape and amplitude with the signatures previously reported from
our observations of 2008 and 2009. The surface magnetic geometry of the star,
reconstructed using the technique of Zeeman-Doppler Imaging, agrees with the
maps obtained in 2008 and 2009, showing that most recognizable features of the
photospheric field of Vega are only weakly distorted by large-scale surface
flows (differential rotation or meridional circulation).Comment: Proceedings of the conference "Stellar polarimetry: from birth to
death", 2011 Jun 27-30, Madiso
Magnetic field, differential rotation and activity of the hot-Jupiter hosting star HD 179949
HD 179949 is an F8V star, orbited by a giant planet at ~8 R* every 3.092514
days. The system was reported to undergo episodes of stellar activity
enhancement modulated by the orbital period, interpreted as caused by
Star-Planet Interactions (SPIs). One possible cause of SPIs is the large-scale
magnetic field of the host star in which the close-in giant planet orbits.
In this paper we present spectropolarimetric observations of HD 179949 during
two observing campaigns (2009 September and 2007 June). We detect a weak
large-scale magnetic field of a few Gauss at the surface of the star. The field
configuration is mainly poloidal at both observing epochs. The star is found to
rotate differentially, with a surface rotation shear of dOmega=0.216\pm0.061
rad/d, corresponding to equatorial and polar rotation periods of 7.62\pm0.07
and 10.3\pm0.8 d respectively. The coronal field estimated by extrapolating the
surface maps resembles a dipole tilted at ~70 degrees. We also find that the
chromospheric activity of HD 179949 is mainly modulated by the rotation of the
star, with two clear maxima per rotation period as expected from a highly
tilted magnetosphere. In September 2009, we find that the activity of HD 179949
shows hints of low amplitude fluctuations with a period close to the beat
period of the system.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical
Societ
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle
On the environment surrounding close-in exoplanets
Exoplanets in extremely close-in orbits are immersed in a local interplanetary medium (i.e. the stellar wind) much denser than the local conditions encountered around the Solar system planets. The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (likely higher for host stars more active than the Sun). Here, we quantitatively investigate the nature of the interplanetary media surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b and HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive mass-loss rates (1.9-8.0 × 10−13 M⊙ yr−1) and the wind properties at the position of the hot Jupiters' orbits (temperature, velocity, magnetic field intensity and pressure). We show that these exoplanets' orbits are supermagnetosonic, indicating that bow shocks are formed surrounding these planets. Assuming planetary magnetic fields similar to Jupiter's, we estimate planetary magnetospheric sizes of 4.1-5.6 planetary radii. We also derive the exoplanetary radio emission released in the dissipation of the stellar wind energy. We find radio fluxes ranging from 0.02 to 0.13mJy, which are challenging to be observed with present-day technology, but could be detectable with future higher sensitivity arrays (e.g. Square Kilometre Array). Radio emission from systems having closer hot Jupiters, such as from τBoob or HD189733b, or from nearby planetary systems orbiting young stars, are likely to have higher radio fluxes, presenting better prospects for detecting exoplanetary radio emissio
The Indolic Diet-Derivative, 3,3′-Diindolylmethane, Induced Apoptosis in Human Colon Cancer Cells through Upregulation of NDRG1
N-myc downstream regulated gene-1 participates in carcinogenesis, angiogenesis, metastases, and anticancer drug resistance. In the present study, we analyzed the expression pattern of N-myc downstream regulated gene-1 following treatment of human colonic cancer cell lines; HCT-116 (well differentiated with wild-type p53 gene) and Colo-320 (poorly differentiated with mutant p53 gene), with 3,3′-diindolylmethane, a well-established proapoptotic agent product derived from indole-3-carbinol. Treatment of Colo-320 and HCT-116 with 3,3′-diindolylmethane disclosed inhibition of cell viability in a dose-dependent manner, mediated through apoptosis induction. The increased expression of N-myc downstream regulated gene-1 was detected only in poorly differentiated colon cancer cells, Colo-320 cell line. Our results suggest that N-myc downstream regulated gene-1 expression is enhanced by 3,3′-diindolylmethane in poorly differentiated cells and followed by induction of apoptosis. 3,3′-diindolylmethane induced apoptosis may represent a new regulator of N-myc downstream regulated gene-1 in poorly differentiated colonic cancer cells
Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
Since the discovery of the transiting super-Earth CoRoT-7b, several
investigations have yielded different results for the number and masses of
planets present in the system, mainly owing to the star's high level of
activity. We re-observed CoRoT-7 in January 2012 with both HARPS and CoRoT, so
that we now have the benefit of simultaneous radial-velocity and photometric
data. This allows us to use the off-transit variations in the star's light
curve to estimate the radial-velocity variations induced by the suppression of
convective blueshift and the flux blocked by starspots. To account for
activity-related effects in the radial-velocities which do not have a
photometric signature, we also include an additional activity term in the
radial-velocity model, which we treat as a Gaussian process with the same
covariance properties (and hence the same frequency structure) as the light
curve. Our model was incorporated into a Monte Carlo Markov Chain in order to
make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We measure
the masses of planets b and c to be 4.73 +/- 0.95 Mearth and 13.56 +/- 1.08
Mearth, respectively. The density of CoRoT-7b is (6.61 +/- 1.72)(Rp/1.58
Rearth)^(-3) g.cm^(-3), which is compatible with a rocky composition. We search
for evidence of an additional planet d, identified by previous authors with a
period close to 9 days. We are not able to confirm the existence of a planet
with this orbital period, which is close to the second harmonic of the stellar
rotation at around 7.9 days. Using Bayesian model selection we find that a
model with two planets plus activity-induced variations is most favoured.Comment: Accepted 2014 July 2. Received 2014 June 30; in original form 2013
May 30 (17 pages, 9 figures
Psychostimulant Misuse Among American Indian, Alaskan Native, or Native Hawaiian College Students in the U.S. From 2015 to 2019
Introduction: This study examines factors associated with psychostimulant misuse, including polysubstance use and social factors, among the understudied American Indian/Alaska Native/Native Hawaiian (AI/AN/NH) college student population.
Methods: Data were from the 2015 to 2019 American College Health Association-National College Health Assessment IIc (ACHA-NCHA IIc) survey. Multivariable logistic regression models and odds ratios were used to estimate associations between psychostimulant misuse and potential risk and protective factors among AI/AN/NH college students, including licit and illicit substance use, social support, relationship factors, exposure to violence or abuse, mental health symptoms, drug and alcohol education, and sample demographics.
Results: Opioid misuse among AI/AN/NH college students significantly increased the odds of using psychostimulants. Specifically, for cocaine use, the adjusted odds ratio (aOR) was 3.17 with a 95% confidence interval (C.I.) of 2.17 to 4.63; for methamphetamine use, the aOR was 38.87 (95% C.I. 19.24-78.52). For amphetamine misuse among non-Tobacco users, the aOR was 5.47 (95% C.I. 3.49-8.55), while among Tobacco users, the aOR was 2.65 (95% C.I. 2.07-3.41). For cocaine and other stimulant misuse, the aOR was 3.64 (95% C.I. 2.30-5.67). Additionally, the use of other types of licit and illicit substances was associated with greater odds of psychostimulant use and misuse. Conversely, factors such as age, living on campus, and residing in parental/guardian housing were linked with lower odds of psychostimulant use and misuse.
Conclusion: Substance use prevention and treatment interventions targeting AI/AN/NH college students should address polysubstance use, including the combined use of opioids and psychostimulants. Substance use interventions should not be siloed to focus narrowly on single substances but rather should leverage potential protective factors against substance use, such as promoting supportive campus and family living conditions and other social support networks, in broad efforts to reduce multiple forms of substance use among AI/AN/NH students
Effect of salt intake on beat‐to‐beat blood pressure nonlinear dynamics and entropy in salt‐sensitive versus salt‐protected rats
Blood pressure exhibits substantial short‐ and long‐term variability (BPV). We assessed the hypothesis that the complexity of beat‐to‐beat BPV will be differentially altered in salt‐sensitive hypertensive Dahl rats (SS) versus rats protected from salt‐induced hypertension (SSBN13) maintained on high‐salt versus low‐salt diet. Beat‐to‐beat systolic and diastolic BP series from nine SS and six SSBN13 rats (http://www.physionet.org) were analyzed following 9 weeks on low salt and repeated after 2 weeks on high salt. BP complexity was quantified by detrended fluctuation analysis (DFA), short‐ and long‐range scaling exponents (αS and αL), sample entropy (SampEn), and traditional standard deviation (SD) and coefficient of variation (CV(%)). Mean systolic and diastolic BP increased on high‐salt diet (P < 0.01) particularly for SS rats. SD and CV(%) were similar across groups irrespective of diet. Salt‐sensitive and ‐protected rats exhibited similar complexity indices on low‐salt diet. On high salt, (1) SS rats showed increased scaling exponents or smoother, systolic (P = 0.007 [αL]) and diastolic (P = 0.008 [αL]) BP series; (2) salt‐protected rats showed lower SampEn (less complex) systolic and diastolic BP (P = 0.046); and (3) compared to protected SSBN13 rats, SS showed higher αL for systolic (P = 0.01) and diastolic (P = 0.005) BP. Hypertensive SS rats are more susceptible to high salt with a greater rise in mean BP and reduced complexity. Comparable mean pressures in sensitive and protective rats when on low‐salt diet coupled with similar BPV dynamics suggest a protective role of low‐salt intake in hypertensive rats. This effect likely reflects better coupling of biologic oscillators.We investigated the non‐linear dynamical properties of blood pressure variability, specifically complexity analysis and detrended fluctuation analysis (DFA), of the systolic and diastolic blood pressure time series in 9 salt sensitive and 6 protected rats. We showed that salt sensitive rats exhibit varying non linear BP dynamics compared to protected rats (smoother time series), irrespective of diet; we also showed the differential impat of salt intake on complexity and DFA metrics in both strains of rats.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122419/1/phy212823_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122419/2/phy212823.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122419/3/phy212823-sup-0001-SupInfo.pd
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