3,959 research outputs found
X-ray method to study temperature-dependent stripe domains in MnAs/GaAs(001)
MnAs films grown on GaAs (001) exhibit a progressive transition between
hexagonal (ferromagnetic) and orthorhombic (paramagnetic) phases at wide
temperature range instead of abrupt transition during the first-order phase
transition. The coexistence of two phases is favored by the anisotropic strain
arising from the constraint on the MnAs films imposed by the substrate. This
phase coexistence occurs in ordered arrangement alternating periodic terrace
steps. We present here a method to study the surface morphology throughout this
transition by means of specular and diffuse scattering of soft x-rays, tuning
the photon energy at the Mn 2p resonance. The results show the long-range
arrangement of the periodic stripe-like structure during the phase coexistence
and its period remains constant, in agreement with previous results using other
techniques.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Magnetic reconfiguration of MnAs/GaAs(001) observed by Magnetic Force Microscopy and Resonant Soft X-ray Scattering
We investigated the thermal evolution of the magnetic properties of MnAs
epitaxial films grown on GaAs(001) during the coexistence of
hexagonal/orthorhombic phases using polarized resonant (magnetic) soft X-ray
scattering and magnetic force microscopy. The results of the diffuse satellite
X-ray peaks were compared to those obtained by magnetic force microscopy and
suggest a reorientation of ferromagnetic terraces as temperature rises. By
measuring hysteresis loops at these peaks we show that this reorientation is
common to all ferromagnetic terraces. The reorientation is explained by a
simple model based on the shape anisotropy energy. Demagnetizing factors were
calculated for different configurations suggested by the magnetic images. We
noted that the magnetic moments flip from an in-plane mono-domain orientation
at lower temperatures to a three-domain out-of-plane configuration at higher
temperatures. The transition was observed when the ferromagnetic stripe width L
is equal to 2.9 times the film thickness d. This is in good agreement with the
expected theoretical value of L = 2.6d.Comment: 16 pages in PD
Ventricular BNP gene expression in acute cardiac overload
INTRODUCTION:B-type natriuretic peptide (BNP) plasma levels have important diagnostic and prognostic implications in heart failure (HF). Recently, aside from its natriuretic effect, antiproliferative and antifibrotic actions of BNP on the cardiovascular system have been described. Under physiological conditions the atria are the main source of this peptide, while its ventricular expression is still controversial. The aim of this work was to evaluate, in an animal model, the ventricular expression of BNP in normal hearts, at baseline and under acute cardiac overload.METHODS:Anesthetized open chest male Wistar rats (n=18) were instrumented with a micromanometer in the right ventricular cavity for pressure assessment. Randomization for three different protocols was then performed: (i) pressure overload for a period of 6 hours (SPr; n = 6), by pulmonary trunk banding, in order to double basal right ventricular systolic pressure; (ii) volume overload with a six-hour perfusion of Dextran 40 (SVol; n = 6), to raise end-diastolic right ventricular pressure fourfold; (iii) sham operated rats (n = 6). Transmural samples from the right ventricular free wall were then obtained for quantification of BNP mRNA by RT and quantitative real-time PCR. The results are expressed as mean+/-SEM (number molecules of mRNA BNP)/(ng total mRNA); p < 0.05.RESULTS:A basal expression of BNP was identified in the sham group (3.6x10(7) +/- 1.7x10(7)). BNP mRNA levels were elevated in both the SPr and SVol groups (+123.1 +/- 46.3% SPr and +171.6 +/- 87.7% SVol).CONCLUSIONS:Acute cardiac pressure and volume overload are associated with increased ventricular BNP gene expression. Our results suggest that BNP may be involved in early ventricular remodeling
Preparation of tetrahydro-1H-xanthen-1-one and chromen-1-one derivatives via a Morita-Baylis-Hillman/oxa-Michael/elimination cascade
The Morita-Baylis-Hillman (MBH) reaction is a carbon-carbon bond forming transformation between an electrophile, typically an aldehyde, and an activated olefin. MBH adducts obtained from 2-hydroxy- benzaldehydes and cyclic enones are potential substrates for the synthesis of xanthenone and chromenone derivatives. In this work, we investigated conditions to obtain tetrahydro-1H-xanthen-1-ones and chromen- 1-ones directly via a Morita-Baylis-Hillman/oxa-Michael/elimination cascade catalyzed by a bifunctional, bicyclic imidazolyl alcohol (BIA), which proved to be an effective catalyst for this transformation. The reactions were performed at room temperature in water to give the products in 10-74 % yield
Submesoscale dispersion in the vicinity of the Deepwater Horizon spill
Reliable forecasts for the dispersion of oceanic contamination are important
for coastal ecosystems, society and the economy as evidenced by the Deepwater
Horizon oil spill in the Gulf of Mexico in 2010 and the Fukushima nuclear plant
incident in the Pacific Ocean in 2011. Accurate prediction of pollutant
pathways and concentrations at the ocean surface requires understanding ocean
dynamics over a broad range of spatial scales. Fundamental questions concerning
the structure of the velocity field at the submesoscales (100 meters to tens of
kilometers, hours to days) remain unresolved due to a lack of synoptic
measurements at these scales. \textcolor{black} {Using high-frequency position
data provided by the near-simultaneous release of hundreds of accurately
tracked surface drifters, we study the structure of submesoscale surface
velocity fluctuations in the Northern Gulf Mexico. Observed two-point
statistics confirm the accuracy of classic turbulence scaling laws at
200m50km scales and clearly indicate that dispersion at the submesoscales is
\textit{local}, driven predominantly by energetic submesoscale fluctuations.}
The results demonstrate the feasibility and utility of deploying large clusters
of drifting instruments to provide synoptic observations of spatial variability
of the ocean surface velocity field. Our findings allow quantification of the
submesoscale-driven dispersion missing in current operational circulation
models and satellite altimeter-derived velocity fields.Comment: 9 pages, 6 figure
Contractile effects of Ghrelin and expression of its receptor GHS-R1a in normal and hypertrophic myocardium
INTRODUCTION:Ghrelin, isolated in 1999, is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R1a). Recent studies suggest that it may influence the function of normal and failing hearts. Nonetheless, it has been difficult to differentiate its effects on the intrinsic properties of the myocardium from the secondary effects resulting from growth hormone release and vasomotor action. This study investigated the contractile effects of ghrelin and expression of its receptor GHS-R1a in normal and hypertrophic myocardium.METHODS:Adult Wistar rats randomly received monocrotaline (MCT; n=9; 60 mg/kg, s.c.) or vehicle (n=7; 1 ml/kg). Three weeks later, after right ventricular (RV) hemodynamic evaluation, the effects of 10(-6) M of a pentapeptide active fragment of ghrelin (fG) were tested on contractile parameters of RV papillary muscles (Normal, n=7; MCT, n=9). GHS-R1a mRNA expression was estimated in RV transmural free-wall samples (Normal, n=7; MCT, n=9), using real-time RT-PCR.RESULTS:In the Normal group, fG reduced active tension (AT), maximum velocity of tension rise (dT/dt(max)) and maximum velocity of tension decline (dT/dt(min)), by 27.9 +/- 4.0%, 28.5 +/- 6.7% and 21.4 +/- 4.2% respectively. In the MCT group, fG reduced AT, dT/dt(max) and dT/dt(min) by 24.1 +/- 6.3%, 24.3 +/- 6.5% and 24.5 +/- 6.1% respectively. GHS-R1a mRNA expression was similar in the two groups (Normal: 2.3*10(5) +/- 5.4*10(4); MCT: 3.0*10(5) +/- 1.1*10(5): p > 0.05).CONCLUSION:This study shows that ghrelin has negative inotropic and lusitropic effects. These effects and expression of its receptor are preserved in RV hypertrophy, suggesting that ghrelin may be a new target in progression to heart failure
Activation profile of pro-inflammatory cytokines in acute cardiac overload
INTRODUCTION:Pro-inflammatory cytokines have been implicated in ventricular remodeling during heart failure progression. In the present study, we investigated the effects of acute volume and RV pressure overload on biventricular hemodynamics and myocardial gene expression of IL-6 and TNF-alpha.METHODS:Male Wistar rats (n = 45) instrumented with RV and LV tip micromanometers were randomly assigned to one of three protocols: i) acute RV pressure overload (PrOv) induced by pulmonary trunk banding in order to double RV peak systolic pressure, for 120 or 360 min; ii) acute volume overload (VolOv) induced by dextran40 infusion (5 ml/h), for 120 or 360 min; iii) Sham. Free wall samples from the RV and LV were collected for mRNA quantification.RESULTS:In the RV, acute overload induced IL-6 and TNF-alpha gene expression, higher in VolOv (IL-6: + 669.7 +/- 263.4%; TNF-alpha: + 5149.9 +/- 1099.0%; 360 min) than in PrOv (IL-6: + 64.9 +/- 44.2%; TNF-alpha: + 628.1 +/- 229.3%; 360 min). In PrOv, TNF-alpha mRNA levels in the LV were increased, in the absence of ventricular overload. IL-6 and TNF-alpha mRNA levels did not correlate in the LV, while in the RV a positive correlation was found (r = 0.574; p < 0.001).CONCLUSIONS:Acute cardiac overload induces overexpression of pro-inflammatory cytokines. This gene activation is not uniform, being higher in volume overload and involving both load-dependent and load-independent mechanisms
J-PLUS: analysis of the intracluster light in the Coma cluster
The intracluster light (ICL) is a luminous component of galaxy clusters
composed of stars that are gravitationally bound to the cluster potential but
do not belong to the individual galaxies. Previous studies of the ICL have
shown that its formation and evolution are intimately linked to the
evolutionary stage of the cluster. Thus, the analysis of the ICL in the Coma
cluster will give insights into the main processes driving the dynamics in this
highly complex system. Using a recently developed technique, we measure the ICL
fraction in Coma at several wavelengths, using the J-PLUS unique filter system.
The combination of narrow- and broadband filters provides valuable information
on the dynamical state of the cluster, the ICL stellar types, and the
morphology of the diffuse light. We use the Chebyshev-Fourier Intracluster
Light Estimator (CICLE) to disentangle the ICL from the light of the galaxies,
and to robustly measure the ICL fraction in seven J-PLUS filters. We obtain the
ICL fraction distribution of the Coma cluster at different optical wavelengths,
which varies from , showing the highest values in the narrowband
filters J0395, J0410, and J0430. This ICL fraction excess is distinctive
pattern recently observed in dynamically active clusters (mergers), indicating
a higher amount of bluer stars in the ICL compared to the cluster galaxies.
Both the high ICL fractions and the excess in the bluer filters are indicative
of a merging state. The presence of younger/lower-metallicity stars the ICL
suggests that the main mechanism of ICL formation for the Coma cluster is the
stripping of the stars in the outskirts of infalling galaxies and, possibly,
the disruption of dwarf galaxies during past/ongoing mergers.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in A&
One-pot organocatalyzed synthesis of tricyclic indolizines
Indolizines and their saturated derivatives are important structural motifs present in several biologically active compounds of both natural and synthetic origin. We describe herein a one-pot approach for the synthesis of tricyclic indolizines catalyzed by a bicyclic imidazole-alcohol. The protocol is based on an aqueous Morita-Baylis-Hillman reaction between pyridine-2-carboxaldehydes and six- or seven-membered cyclic enones, followed by sequential intramolecular cyclization and dehydration. So, in a single operational step two new bonds (C-C and C-N) are formed in an organocatalyzed process that takes place in simple conditions (stirring in water at 60 °C for 12 h) and with great atom economy (water as the sole byproduct), affording the purified compounds in yields ranging from 19 to 70%. The facility of the cyclization strongly depends on the size of the cycloalkenone ring: while MBH adducts derived from six-, seven- or eight-membered cycloenones are readily transformed into the corresponding indolizines, cyclopentenone-derived MBH adducts do not cyclize. A competition experiment revealed that cycloheptenone- derived MBH adducts cyclize faster than cyclohexenone-derived adducts. Model DFT calculations have been performed to rationalize these reactivity trends
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