1,688 research outputs found
Slow and velocity-tunable beams of metastable He by multistage Zeeman deceleration
Metastable helium molecules (He) have been generated by striking a
discharge in a supersonic expansion of helium gas from a pulsed valve. When
operating the pulsed valve at room temperature, 77K, and 10K, the mean velocity
of the supersonic beam was measured to be 1900m/s, 980m/s, and 530m/s,
respectively. A 55-stage Zeeman decelerator operated in a phase-stable manner
was then used to further reduce the beam velocity and tune it in the range
between 100 and 150m/s. The internal-state distribution of the decelerated
sample was established by photoionization spectroscopy.Comment: 10 pages, 7 figure
The Nearby and Extremely Metal-Poor Galaxy CGCG 269-049
We present Hubble Space Telescope (HST) and Spitzer Space Telescope images
and photometry of the extremely metal-poor (Z = 0.03 Z_sol) blue dwarf galaxy
CGCG 269-049. The HST images reveal a large population of red giant and
asymptotic giant branch stars, ruling out the possibility that the galaxy has
recently formed. From the magnitude of the tip of the red giant branch, we
measure a distance to CGCG 269-049 of only 4.9 +/- 0.4 Mpc. The spectral energy
distribution of the galaxy between ~3.6 - 70 microns is also best fitted by
emission from predominantly ~10 Gyr old stars, with a component of thermal dust
emission having a temperature of 52 +/- 10 K. The HST and Spitzer photometry
indicate that more than 60% of CGCG 269-049's stellar mass consists of stars
~10 Gyr old, similar to other local blue dwarf galaxies. Our HST H-alpha image
shows no evidence of a supernova-driven outflow that could be removing metals
from the galaxy, nor do we find evidence that such outflows occurred in the
past. Taken together with CGCG 269-049's large ratio of neutral hydrogen mass
to stellar mass (~10), these results are consistent with recent simulations in
which the metal deficiency of local dwarf galaxies results mainly from
inefficient star formation, rather than youth or the escape of supernova
ejecta.Comment: 35 Pages, 7 Figures, accepted for publication in ApJ; new version
corrects errors in Table 1, Figure 3, and related calculations in tex
Improved Pseudofermion Approach for All-Point Propagators
Quark propagators with arbitrary sources and sinks can be obtained more
efficiently using a pseudofermion method with a mode-shifted action.
Mode-shifting solves the problem of critical slowing down (for light quarks)
induced by low eigenmodes of the Dirac operator. The method allows the full
physical content of every gauge configuration to be extracted, and should be
especially helpful for unquenched QCD calculations. The method can be applied
for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert,
Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The
statistical properties of the method are examined and examples of physical
processes under study are presented.Comment: LateX, 26 pages, 10 eps figure
Effects of endotoxin infusion on mean systemic filling pressure and flow resistance to venous return
Mean systemic filling pressure (Psf) is an indicator of the filling state of the systemic circulation. Cardiac output (Q′) is related linearly to the difference between Psf and central venous pressure (Pcv), according to:Q′ = (Psf -Pcv)/Rsf, where Rsf is the flow resistance downstream from the sites where blood pressure is equal to Psf In 16 anaesthetized pigs we evaluated Psf, Rsf and Q′ during baseline conditions, continuous endotoxin infusion and after subsequent fluid loading. Psf and Rsf were determined from simultaneous measurements of Q′ and Pcv at seven levels of lung inflation. The following results were obtained. Psf was 8.1 ±1.8 mm Hg (mean ± SD) during baseline conditions, increased after endotoxin infusion to 9.9 ± 3.2 mm Hg (P = 0.04) and remained the same after infusion of 18 ml · kg-1 of Ringer's lactate. Rsf increased from 0.34 ± 0.07 to 0.80 ± 0.34 mm Hg · ml-1 · s by endotoxin and decreased after fluid infusion to 0.58 ± 0.14. Q′ changed inversely proportional to Rsf (P = 0.001). Rsf changes were highly correlated with the changes in total systemic flow resistance (RS) (P < 0.001). Endotoxin caused haemoconcentration and a decrease in plasma volume. The stability of Psf during endotoxin infusion and after volume loading indicate that the stressed volume was well maintained and changes in blood volume are compensated by changes in nonstressed volume. The increase in Rsf can be attributed to arteriolar vasoconstriction, venous vasoconstriction and haemoconcentration
Flavour Breaking Effects of Wilson twisted mass fermions
We study the flavour breaking effects appearing in the Wilson twisted mass
formulation of lattice QCD. In this quenched study, we focus on the mass
splitting between the neutral and the charged pion, determining the neutral
pion mass with a stochastic noise method to evaluate the disconnected
contributions. We find that these disconnected contributions are significant.
Using the Osterwalder-Seiler interpretation of the connected piece of the
neutral pion correlator, we compute the corresponding neutral pion mass to
study with more precision the scaling behaviour of the mass splitting.Comment: 15 pages, 2 figure
The H-alpha and Infrared Star Formation Rates for the Nearby Field Galaxy Survey
We investigate the H-alpha and infrared star formation rate (SFR) diagnostics
for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in
our sample, we derive H-alpha fluxes (included here) from integrated spectra.
There is a strong correlation between the ratio of far-infrared to optical
luminosities L(FIR)/L(H-alpha) and the extinction E(B-V) measured with the
Balmer decrement. Before reddening correction, the SFR(IR) and SFR(H-alpha) are
related to each other by a power-law. Correction of the SFR(H-alpha) for
extinction using the Balmer decrement and a classical reddening curve both
reduces the scatter in the SFR(IR)-SFR(H-alpha) correlation and results in a
much closer agreement (within ~10%) between the two SFR indicators. This SFR
relationship spans 4 orders of magnitude and holds for all Hubble types with
IRAS detections in the NFGS. A constant ratio between the SFR(IR) and
SFR(H-alpha) for all Hubble types, including early types (S0-Sab), suggests
that the IR emission in all of these objects results from a young stellar
population.Comment: 23 pages, 5 figures, 1 table. Accepted for publication in the
Astronomical Journal. V2: Important changes: IRAS fluxes updated. Only
moderate and good quality IRAS FIR fluxes are now used, resulting in slight
changes to the equations and figures. The IR and H-alpha SFRs now agree to
within ~10%, rather than ~30% as quoted previousl
{\eta} and {\eta}' mesons from Nf=2+1+1 twisted mass lattice QCD
We determine mass and mixing angles of eta and eta' states using Nf=2+1+1
Wilson twisted mass lattice QCD. We describe how those flavour singlet states
need to be treated in this lattice formulation. Results are presented for three
values of the lattice spacing, a=0.061 fm, a=0.078 fm and a=0.086 fm, with
light quark masses corresponding to values of the charged pion mass in a range
of 230 to 500 MeV and fixed bare strange and charm quark mass values. We obtain
557(15)(45) MeV for the eta mass (first error statistical, second systematic)
and 44(5) degrees for the mixing angle in the quark flavour basis,
corresponding to -10(5) degrees in the octet-singlet basis.Comment: 28 pages, 9 figures, version to appear in JHEP, extended discussion
of autocorrelation times and comparison to results available in the
literature, added a comment for FS-effects and clarified the description of
our blocking procedur
METHANOGENIC CONVERSION OF 3-S-METHYLMERCAPTOPROPIONATE TO 3-MERCAPTOPROPIONATE
Anaerobic metabolism of dimethylsulfoniopropionate, an osmolyte of marine algae, in anoxic intertidal sediments involves either cleavage to dimethylsulfide or demethylation to 3-S-methylmercaptopropionate (MMPA) and subsequently to 3-mercaptopropionate. The methanogenic archaea Methanosarcina sp. strain MTP4 (DSM 6636), Methanosarcina acetivorans DSM 2834, and Methanosarcina (Methanolobus) siciliae DSM 3028 were found to use MMPA as a growth substrate and to convert it stoichiometrically to 3-mercaptopropionate. Approximately 0.75 mol of methane was formed per mol of MMPA degraded; methanethiol was not detected as an intermediate. Eight other methanogenic strains did not carry out this conversion. We also studied the conversion of MMPA in anoxic marine sediment slurries. Addition of MMPA (500 mu M) resulted in the production of methanethiol which was subsequently converted to methane (417 mu M). In the presence of the antibiotics ampicillin, vancomycin, and kanamycin (20 mu g/ml each), 275 mu M methane was formed from 380 mu M MMPA; no methanethiol was formed during these incubations. Only methanethiol was formed from MMPA when 2-bromoethanesulfonate (25 mM) was added to a sediment suspension. These results indicate that in natural environments MMPA could be directly or indirectly a substrate for methanogenic archaea.</p
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