796 research outputs found
Revisiting the statistical analysis of pyroclast density and porosity data
Explosive volcanic eruptions are commonly characterized based on a thorough analysis of the generated deposits. Amongst other characteristics in physical volcanology, density and porosity of juvenile clasts are some of the most frequently used to constrain eruptive dynamics. In this study, we evaluate the sensitivity of density and porosity data to statistical methods and introduce a weighting parameter to correct issues raised by the use of frequency analysis. Results of textural investigation can be biased by clast selection. Using statistical tools as presented here, the meaningfulness of a conclusion can be checked for any data set easily. This is necessary to define whether or not a sample has met the requirements for statistical relevance, i.e. whether a data set is large enough to allow for reproducible results. Graphical statistics are used to describe density and porosity distributions, similar to those used for grain-size analysis. This approach helps with the interpretation of volcanic deposits. To illustrate this methodology, we chose two large data sets: (1) directed blast deposits of the 3640-3510 BC eruption of Chachimbiro volcano (Ecuador) and (2) block-and-ash-flow deposits of the 1990-1995 eruption of Unzen volcano (Japan). We propose the incorporation of this analysis into future investigations to check the objectivity of results achieved by different working groups and guarantee the meaningfulness of the interpretation
The Domain Chaos Puzzle and the Calculation of the Structure Factor and Its Half-Width
The disagreement of the scaling of the correlation length xi between
experiment and the Ginzburg-Landau (GL) model for domain chaos was resolved.
The Swift-Hohenberg (SH) domain-chaos model was integrated numerically to
acquire test images to study the effect of a finite image-size on the
extraction of xi from the structure factor (SF). The finite image size had a
significant effect on the SF determined with the Fourier-transform (FT) method.
The maximum entropy method (MEM) was able to overcome this finite image-size
problem and produced fairly accurate SFs for the relatively small image sizes
provided by experiments.
Correlation lengths often have been determined from the second moment of the
SF of chaotic patterns because the functional form of the SF is not known.
Integration of several test functions provided analytic results indicating that
this may not be a reliable method of extracting xi. For both a Gaussian and a
squared SH form, the correlation length xibar=1/sigma, determined from the
variance sigma^2 of the SF, has the same dependence on the control parameter
epsilon as the length xi contained explicitly in the functional forms. However,
for the SH and the Lorentzian forms we find xibar ~ xi^1/2.
Results for xi determined from new experimental data by fitting the
functional forms directly to the experimental SF yielded xi ~ epsilon^-nu} with
nu ~= 1/4 for all four functions in the case of the FT method, but nu ~= 1/2,
in agreement with the GL prediction, in the the case of the MEM. Over a wide
range of epsilon and wave number k, the experimental SFs collapsed onto a
unique curve when appropriately scaled by xi.Comment: 15 pages, 26 figures, 1 tabl
Square patterns in Rayleigh-Benard convection with rotation about a vertical axis
We present experimental results for Rayleigh-Benard convection with rotation
about a vertical axis at dimensionless rotation rates in the range 0 to 250 and
upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with
predictions of linear stability analysis. For rotation rates greater than 70
and close to onset, the patterns are cellular with local four-fold coordination
and differ from the theoretically expected Kuppers-Lortz unstable state. Stable
as well as intermittent defect-free square lattices exist over certain
parameter ranges. Over other ranges defects dynamically disrupt the lattice but
cellular flow and local four-fold coordination is maintained.Comment: ReVTeX, 4 pages, 7 eps figures include
Ammonia and other parent molecules in comet 10P/Tempel 2 from Herschel/HIFI and ground-based radio observations
The Jupiter-family comet 10P/Tempel 2 was observed during its 2010 return
with the Herschel Space Observatory. We present here the observation of the (J,
K) = (1, 0)-(0, 0) transition of ammonia at 572 GHz in this comet with the
Heterodyne Instrument for the Far Infrared (HIFI) of Herschel. We also report
on radio observations of other molecules (HCN, CH3OH, H2S and CS) obtained
during the 1999 return of the comet with the CSO telescope and the JCMT, and
during its 2010 return with the IRAM 30-m telescope. Molecular abundances
relative to water are 0.09%, 1.8%, 0.4%, and 0.08% for HCN, CH3OH, H2S, and CS,
respectively. An abundance of 0.5% for NH3 is obtained, which is similar to the
values measured in other comets. The hyperfine structure of the ammonia line is
resolved for the first time in an astronomical source. Strong anisotropy in the
outgassing is present in all observations from 1999 to 2010 and is modelled to
derive the production rates.Comment: 6 pages and 8 figures. Accepted for publication in Astronomy &
Astrophysic
Evidence for the interaction of Endophilin A3 with endogenous K(Ca)2.3 channels in PC12 cells
Background/Aims: Small-conductance calcium-activated (SK) channels play an important role by controlling the after-hyperpolarization of excitable cells. The level of expression and density of these channels is an essential factor for controlling different cellular functions. Several studies showed a co-localization of KCa2.3 channels and Endophilin A3 in different tissues. Endophilin A3 belongs to a family of BAR- and SH3 domain containing proteins that bind to dynamin and are involved in the process of vesicle scission in clathrin-mediated endocytosis. Methods: Using the yeast two-hybrid system and the GST pull down assay we demonstrated that Endophilin A3 interacts with the N-terminal part of KCa2.3 channels. In addition, we studied the impact of this interaction on channel activity by patch clamp measurements in PC12 cells expressing endogenous KCa2.3 channels. KCa2.3 currents were activated by using pipette solutions containing 1 µM free Ca(2+). Results: Whole-cell measurements of PC12 cells transfected with Endophilin A3 showed a reduction of KCa2.3 specifc Cs(+) currents indicating that the interaction of Endophilin A3 with KCa2.3 channels also occurs in mammalian cells and that this interaction has functional consequences for current flowing through KCa2.3 channels. Since KCa2.3 specific currents could be increased in PC12 cells transfected with Endophilin A3 with DC-EBIO (30 µM), a known SK-channel activator, these data also implicate that Endophilin A3 did not significantly remove KCa2.3 channels from the membrane but changed the sensitivity of the channels to Ca(2+) which could be overcome by DC-EBIO. Conclusion: This interaction seems to be important for the function of KCa2.3 channels and might therefore play a significant role in situations where channel activation is pivotal for cellular function
Contribution to a macromycete survey of the states of Rio Grande do Sul and Santa Catarina in Brazil
Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact
On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission
crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material
ejected by the impact expanded into the normal coma, produced by ordinary
cometary activity.
The characteristics of the non-impact coma and cloud produced by the impact
were studied by observations in the visible wavelengths and in the near-IR. The
scattering characteristics of the "normal" coma of solid particles were studied
by comparing images in various spectral regions, from the UV to the near-IR.
For the non-impact coma, a proxy of the dust production has been measured in
various spectral regions. The presence of sublimating grains has been detected.
Their lifetime was found to be about 11 hours. Regarding the cloud produced by
the impact, the total geometric cross section multiplied by the albedo was
measured as a function of the color and time. The projected velocity appeared
to obey a Gaussian distribution with the average velocity of the order of 115
m/s. By comparing the observations taken about 3 hours after the impact, we
have found a strong decrease in the cross section in J filter, while that in Ks
remained almost constant. This is interpreted as the result of sublimation of
grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&
Bowel Preparation for Colonoscopy with Sodium Phosphate Solution versus Polyethylene Glycol-Based Lavage: A Multicenter Trial
Background: Adequate bowel preparation is essential for
accurate colonoscopy. Both oral sodium phosphate (NaP) and
polyethylene glycol-based lavage (PEG-ELS) are used predominantly
as bowel cleansing modalities. NaP has gained popularity due to
low drinking volume and lower costs. The purpose of this
randomized multicenter observer blinded study was to compare
three groups of cleansing (NaP, NaP + sennosides, PEG-ELS +
sennosides) in reference to tolerability, acceptance, and
cleanliness. Patient and Methods: 355 outpatients between 18 and
75 years were randomized into three groups (A, B, C) receiving NaP =
A, NaP, and sennosides = B or PEG-ELS and sennosides = C.
Gastroenterologists performing colonoscopies were blinded to the
type of preparation. All patients documented tolerance and adverse
events. Vital signs, premedication, completeness, discomfort, and
complications were recorded. A quality score (0–4) of cleanliness
was generated. Results: The three groups were similar
with regard to age, sex, BMI, indication for colonoscopy, and
comorbidity. Drinking volumes (L) (A = 4.33 + 1.2, B = 4.56 + 1.18, C = 4.93 + 1.71) were in favor of NaP
(P = .005). Discomfort from
ingested fluid was recorded in A = 39.8% (versus C: P = .015),
B = 46.6% (versus C: P = .147), and C = 54.6%. Differences in tolerability and acceptance between the three groups were
statistically not significant. No differences in adverse events
and the cleanliness effects occurred in the three groups (P = .113).
The cleanliness quality scores 0–2 were calculated in A:
77.7%, B: 86.7%, and C: 85.2%. Conclusions:
These data fail to demonstrate significant differences in
tolerability, acceptance, and preparation quality between the
three types of bowel preparation for colonoscopy. Cleansing with
NaP was not superior to PEG-ELS
Rotating Convection in an Anisotropic System
We study the stability of patterns arising in rotating convection in weakly
anisotropic systems using a modified Swift-Hohenberg equation. The anisotropy,
either an endogenous characteristic of the system or induced by external
forcing, can stabilize periodic rolls in the K\"uppers-Lortz chaotic regime.
For the particular case of rotating convection with time-modulated rotation
where recently, in experiment, chiral patterns have been observed in otherwise
K\"uppers-Lortz-unstable regimes, we show how the underlying base-flow breaks
the isotropy, thereby affecting the linear growth-rate of convection rolls in
such a way as to stabilize spirals and targets. Throughout we compare
analytical results to numerical simulations of the Swift-Hohenberg equation
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