22,207 research outputs found
Improved forecasts for the baryon acoustic oscillations and cosmological distance scale
We present the cosmological distance errors achievable using the baryon
acoustic oscillations as a standard ruler. We begin from a Fisher matrix
formalism that is upgraded from Seo & Eisenstein (2003). We isolate the
information from the baryonic peaks by excluding distance information from
other less robust sources. Meanwhile we accommodate the Lagrangian displacement
distribution into the Fisher matrix calculation to reflect the gradual loss of
information in scale and in time due to nonlinear growth, nonlinear bias, and
nonlinear redshift distortions. We then show that we can contract the
multi-dimensional Fisher matrix calculations into a 2-dimensional or even
1-dimensional formalism with physically motivated approximations. We present
the resulting fitting formula for the cosmological distance errors from galaxy
redshift surveys as a function of survey parameters and nonlinearity, which
saves us going through the 12-dimensional Fisher matrix calculations. Finally,
we show excellent agreement between the distance error estimates from the
revised Fisher matrix and the precision on the distance scale recovered from
N-body simulations.Comment: Submitted to ApJ, 21 pages, LaTe
Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of -(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl)
The infrared spectra of the quasi-two-dimensional organic conductors
-(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl) were measured in
the range from 50 to 7000 \cm down to low temperatures in order to explore the
influence of electronic correlations in quarter-filled metals. The
interpretation of electronic spectra was confirmed by measurements of pressure
dependant reflectance of -(BEDT-TTF)KHg(SCN) at T=300 K. The
signatures of charge order fluctuations become more pronounced when going from
the NH salt to Rb and further to Tl compounds. On reducing the temperature,
the metallic character of the optical response in the NH and Rb salts
increases, and the effective mass diminishes. For the Tl compound, clear
signatures of charge order are found albeit the metallic properties still
dominate. From the temperature dependence of the electronic scattering rate the
crossover temperature is estimated below which the coherent charge-carriers
response sets in. The observations are in excellent agreement with recent
theoretical predictions for a quarter-filled metallic system close to charge
order
Pressure effects on the heavy-fermion antiferromagnet CeAuSb2
The f-electron compound CeAuSb2, which crystallizes in the ZrCuSi2-type
tetragonal structure, orders antiferromagnetically between 5 and 6.8 K, where
the antiferromagnetic transition temperature T_N depends on the occupancy of
the Au site. Here we report the electrical resistivity and heat capacity of a
high-quality crystal CeAuSb2 with T_N of 6.8 K, the highest for this compound.
The magnetic transition temperature is initially suppressed with pressure, but
is intercepted by a new magnetic state above 2.1 GPa. The new phase shows a
dome shape with pressure and coexists with another phase at pressures higher
than 4.7 GPa. The electrical resistivity shows a T^2 Fermi liquids behavior in
the complex magnetic state, and the residual resistivity and the T^2
resistivity coefficient increases with pressure, suggesting the possibility of
a magnetic quantum critical point at a higher pressure.Comment: 5 pages, 5 firure
Impacts of water pH on the toxicity of fluoxetine on Daphnia magna: a multi-generational study
Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), has been widely
prescribed as anti-depressant. While FLX has been frequently detected in surface
waters, sediments and biota, only limited information is available on its in vivo toxicity, particularly in invertebrates, under changing water pH. In the present
study, the ecotoxicity of FLX (pKa = 9.8) was investigated in different pH levels
(6.8, 8.3, and 9.2) using Daphnia magna. Daphnia neonates ( (F0) were exposed
to 0, solvent control, 31.3, 62.5, 125, 250, 500, or 1000 Ī¼g/L for 48 hr and its
effects on survivals (EC20, 50 and 75) were determined. Moreover, Daphnia
neonates (The first brood daphnids from the chronic tests were discarded and the
second brood daphnids (F1) were employed for the multigenerational acute test
within 12 hours. F1 neonates were further exposed to 0, solvent control, 31.3,
62.5, 125, 250, or 500 Ī¼g/L for 48 hr and their survivals (EC20, 50 and 75) were
determined. F0 juveniles exposed to 0 or 55.6 Ī¼g/L at 10 d were measured for
MDA. After 48 hr of F0 and F1 exposure, the EC50 significantly decreased (p <
0.05) at 6.17 Ī¼g/L of FLX at all tested pHs. Moreover, after 21 d F0 exposure, the
reproduction showed an increasing trend until 55.6 Ī¼g/L and significantly
decreased at 166.7 Ī¼g/L at pH 9.2. F1 neonates showed significantly decreased
body length after 21 d exposure to 2.06, 6.17, 18.5 and 55.6 Ī¼g/L at pH 9.2.
Malformation of F1 daphnids development was also observed at 2.06 Ī¼g/L to 500
Ī¼g/L. MDA concentration was also demonstrated increasing trends in all pHs and
significantly increased at 55.6 Ī¼g/L at pH 6.8 and 9.2. Our observation clearly
indicates that survival, reproduction, and growth performance in aquatic
invertebrate can be adversely affected by FLX and the toxicity increases as water
pH increases. A greater amount of uncharged ions from FLX has increased
Reactive Oxidative Stress (ROS), MDA, by the ionic speciation at higher pH.
Increased MDA concentration affected the mortality of F0 daphnids. Increased F1
daphnids population demonstrated significantly greater toxicity. As a result, the
toxicity of FLX has increased acutely, chronically, and multigenerational effects
by increasing pH levels. Consequences of longer-term exposure over multigenerations warrant further investigation
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Effect of Time-of-Flight and Regularized Reconstructions on Quantitative Measurements and Qualitative Assessments in Newly Diagnosed Prostate Cancer With 18F-Fluorocholine Dual Time Point PET/MRI.
Recent technical advances in positron emission tomography/magnetic resonance imaging (PET/MRI) technology allow much improved time-of-flight (TOF) and regularized iterative PET reconstruction regularized iterative reconstruction (RIR) algorithms. We evaluated the effect of TOF and RIR on standardized uptake values (maximum and peak SUV [SUVmax and SUVpeak]) and their metabolic tumor volume dependencies and visual image quality for 18F-fluorocholine PET/MRI in patients with newly diagnosed prostate cancer. Fourteen patients were administered with 3 MBq/kg of 18F-fluorocholine and scanned dynamically for 30 minutes. Positron emission tomography images were divided to early and late time points (1-6 minutes summed and 7-30 minutes summed). The values of the different SUVs were documented for dominant PET-avid lesions, and metabolic tumor volume was estimated using a 50% isocontour and SUV threshold of 2.5. Image quality was assessed via visual acuity scoring (VAS). We found that incorporation of TOF or RIR increased lesion SUVs. The lesion to background ratio was not improved by TOF reconstruction, while RIR improved the lesion to background ratio significantly ( P < .05). The values of the different VAS were all significantly higher ( P < .05) for RIR images over TOF, RIR over non-TOF, and TOF over non-TOF. In conclusion, our data indicate that TOF or RIR should be incorporated into current protocols when available
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