3,073 research outputs found
Influence of rotational force fields on the determination of the work done on a driven Brownian particle
For a Brownian system the evolution of thermodynamic quantities is a
stochastic process. In particular, the work performed on a driven colloidal
particle held in an optical trap changes for each realization of the
experimental manipulation, even though the manipulation protocol remains
unchanged. Nevertheless, the work distribution is governed by established laws.
Here, we show how the measurement of the work distribution is influenced by the
presence of rotational, i.e. nonconservative, radiation forces. Experiments on
particles of different materials show that the rotational radiation forces, and
therefore their effect on the work distributions, increase with the particle
refractive index.Comment: 12 pages, 4 figure
Dating of Old Lime Based Mixtures with the "Pure Lime Lumps" Technique
A number of studies carried out over the last forty years describe the application of radiocarbon dating of lime mixtures such as mortars, plasters and renders. Despite the fact that this method is very simple in principle, several studies have highlighted various practical challenges and factors that must be considered. These arise mainly from the contamination of samples with carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin including limestone sand.
However, recently studies have shown that accurate sample processing allow a significant reduction of these error sources and moreover adoption of a special sampling procedure based on the careful selection of lumps of incompletely mixed lime, provides an interesting alternative that avoids problems associated with contamination. The founding principle underlying this technique is the use of the pure lime lumps. These are thought to originate from imperfect mixing and are most prevalent in mortars, renders and plasters predating mechanical mixing. Previous sampling methods for radiocarbon dating did not discriminate between pure and contaminated lime lumps. As pure lumps contain the same lime as that used in other parts of the mixtures but importantly are free of contaminants such as sand grains or under burned pieces of limestone, they can dramatically reduce the errors in the radiocarbon dating
The Megamaser Cosmology Project. VII. Investigating disk physics using spectral monitoring observations
We use single-dish radio spectra of known 22 GHz HO megamasers, primarily
gathered from the large dataset observed by the Megamaser Cosmology Project, to
identify Keplerian accretion disks and to investigate several aspects of the
disk physics. We test a mechanism for maser excitation proposed by Maoz & McKee
(1998), whereby population inversion arises in gas behind spiral shocks
traveling through the disk. Though the flux of redshifted features is larger on
average than that of blueshifted features, in support of the model, the
high-velocity features show none of the predicted systematic velocity drifts.
We find rapid intra-day variability in the maser spectrum of ESO 558-G009 that
is likely the result of interstellar scintillation, for which we favor a nearby
( pc) scattering screen. In a search for reverberation in six
well-sampled sources, we find that any radially-propagating signal must be
contributing 10% of the total variability. We also set limits on the
magnetic field strengths in seven sources, using strong flaring events to check
for the presence of Zeeman splitting. These limits are typically 200--300 mG
(), but our most stringent limits reach down to 73 mG for the galaxy
NGC 1194.Comment: Accepted for publication in Ap
Direct UV observations of the circumstellar envelope of alpha Orionis
Observations were made in the IUE LWP camera, low dispersion mode, with alpha Ori being offset various distances from the center of the Long Wavelength Large Aperture along its major axis. Signal was acquired at all offset positions and is comprised of unequal components of background/dark counts, telescope-scattered light, and scattered light emanating from the extended circumstellar shell. The star is known from optical and infrared observations to possess an extended, arc-minute sized, shell of cool material. Attempts to observe this shell with the IUE are described, although the deconvolution of the stellar signal from the telescope scattered light requires further calibration effort
The Megamaser Cosmology Project. X. High Resolution Maps and Mass Constraint for SMBHs
We present high resolution (sub-mas) VLBI maps of nuclear H2O megamasers for
seven galaxies. In UGC6093, the well-aligned systemic masers and high-velocity
masers originate in an edge-on, flat disk and we determine the mass of the
central SMBH to be M_SMBH = 2.58*10^7Msun(+-7%). For J1346+5228, the
distribution of masers is consistent with a disk, but the faint high-velocity
masers are only marginally detected, and we constrain the mass of the SMBH to
be in the range 1.5-2.0*10^7Msun. The origin of the masers in Mrk1210 is less
clear, as the systemic and high-velocity masers are misaligned and show a
disorganized velocity structure. We present one possible model in which the
masers originate in a tilted, warped disk, but we do not rule out the
possibility of other explanations including outflow masers. In NGC6926, we
detect a set of redshifted masers, clustered within a pc of each other, and a
single blueshifted maser about 4.4pc away, an offset that would be unusually
large for a maser disk system. Nevertheless, if it is a disk system, we
estimate the enclosed mass to be M_SMBH<4.8*10^7 Msun . For NGC5793, we detect
redshifted masers spaced about 1.4pc from a clustered set of blueshifted
features. The orientation of the structure supports a disk scenario as
suggested by Hagiwara et al.(2001). We estimate the enclosed mass to be M
SMBH<1.3*10^7 Msun. For NGC2824 and J0350-0127, the masers may be associated
with pc or sub-pc scale jets or outflows.Comment: Accepted by Ap
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