893 research outputs found
Submillimetric spectroscopic observations of volatiles in comet C/2004 Q2 (Machholz)
We aim to determine the production rates of several parent and product
volatiles and the 12C/13C isotopic carbon ratio in the long-period comet C/2004
Q2 (Machholz), which is likely to originate from the Oort Cloud. The line
emission from several molecules in the coma was measured with high
signal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU by
means of high-resolution spectroscopic observations using the Submillimeter
Telescope (SMT). We have obtained production rates of several volatiles (CH3OH,
HCN, H13CN, HNC, H2CO, CO and CS) by comparing the observed and simulated
line-integrated intensities. Furthermore, multiline observations of the CH3OH
(7-6) series allow us to estimate the rotational temperature using the rotation
diagram technique. We find that the CH3OH population distribution of the levels
sampled by these lines can be described by a rotational temperature of 40 \pm 3
K. Derived mixing ratios relative to hydrogen cyanide are
CO/CH3OH/H2CO/CS/HNC/H13CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a
pointing offset of 8" due to the uncertain ephemeris at the time of the
observations and the telescope pointing error. The measured relative molecular
abundances in C/2004 Q2 (Machholz) are between low- to typical values of those
obtained in Oort Cloud comets, suggesting that it has visited the inner solar
system previously and undergone thermal processing. The HNC/HCN abundance ratio
of ~3.1% is comparable to that found in other comets, accounting for the
dependence on the heliocentric distance, and could possibly be explained by
ion-molecule chemical processes in the low-temperature atmosphere. From a
tentative H13CN detection, the measured value of 97 \pm 30 for the H12CN/H13CN
isotopologue pair is consistent with a telluric value.Comment: 14 pages with 11 figures, abridged abstrac
Effects of micelle nature and concentration on the acid dissociation constants of the metal extractor PADA
The pyridine-2-azo-p-dimethylaniline (PADA) ligand presents two acid dissociation constants, being pKa1 related to the pyridinium and pKa2 related to the anilinium residue. These have been measured by spectrophotometric titrations in aqueous solutions containing either the anionic (SDS), or the non–ionic (Triton X-100) or the cationic (DTAC) surfactants. The pKai shifts of the charged systems from that of the PADA/Triton X-100 reference (∆pKai0) are compared. For PADA/DTAC ∆pKa10 = 0.05 and ∆pKa20 = 0.6. For PADA/SDS ∆pKa10 = 2.1 and ∆pKa20 = 2.1 both yielding the value of -126 mV for the surface potential (ψ) of SDS. The ψ value, lying between the calculated Stern potential and the zeta potential, indicates that the dye is located on the SDS micelles between the fixed and the shear layer. In contrast, the behaviour of PADA/DTAC is explained assuming that the positively charged deprotonation sites of PADA are forced to protrude towards the bulk solvent by the positive charges of DTAC micelles. The shifts of the apparent pKai from the aqueous values (∆pKaiw) have also been analysed. Concerning PADA/Triton X-100, the shifts ∆pKa1w = -0.1 and ∆pKa2w = -0.9 are rationalized in terms of dielectric constant reduction at the reaction sites. Concerning PADA/DTAC, ∆pKa1w= -0.05 and ∆pKa2w= -0.3 whereas, for PADA/SDS, ∆pKa1w = 2.0 and ∆pKa2w = 1.2. The pKa2w values decrease on raising the surfactant concentrations for all the investigated systems. This behaviour is explained assuming that the increase of the overall micellar surface and, by consequence, of the reaction sites number, results in a site dilution effect which disfavours proton association. The addition of NaCl induces changes of pKa1 and pKa2 which are explained in terms of (large) reduction of ψ for PADA/SDS and of (small) reduction of the dielectric constant for the other systems
A survey of volatile species in Oort cloud comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) at millimeter wavelengths
The line emission in the coma was measured in the comets C/2001 Q4 (NEAT) and
C/2002 T7 (LINEAR), that were observed on five consecutive nights, 7-11 May
2004, at heliocentric distances of 1.0 and 0.7 AU, respectively, by means of
high-resolution spectroscopy using the 10-m Submillimeter Telescope (SMT). We
present a search for six parent- and product-volatile species (HCN, H2CO, CO,
CS, CH3OH, and HNC) in both comets. Multiline observations of the CH3OH J = 5-4
series allow us to estimate the rotational temperature using the rotation
diagram technique. We derive rotational temperatures of 54(9) K for C/2001 Q4
(NEAT) and 119(34) K for C/2002 T7 (LINEAR) that are roughly consistent with
observations of other comets at similar distances from the Sun. The gas
production rates of material are computed using a spherically symmetric
molecular excitation code that includes collisions between neutrals and
electrons. We find an HCN production rate of 2.96(5)e26 molec.s-1 for comet
C/2001 Q4 (NEAT), corresponding to a mixing ratio with respect to H2O of
1.12(2)e-3. The mean HCN production rate during the observing period is
4.54(10)e26 molec.s-1 for comet C/2002 T7 (LINEAR), which gives a Q_HCN/Q_H2O
mixing ratio of 1.51(3)e-3. With systematically lower mixing ratios in comet
C/2001 Q4 (NEAT), production rate ratios of the observed species with respect
to H2O lie within the typical ranges of dynamically new comets in both objects.
We find a relative low abundance of CO in C/2001 Q4 (NEAT) compared to the
observed range in other comets based on millimeter/submillimeter observations,
and a significant upper limit on the CO production in C/2002 T7 (LINEAR) is
derived. Depletion of CO suggests partial evaporation from the surface layers
during previous visits to the outer Solar System and agrees with previous
measurements of dynamically new comets.Comment: 20 pages, 18 figures. Minor changes to match the published versio
Identity formation and public perception in the history of American Mormonism
This study inquires into the institutional identity of the Church of Jesus Christ of Latter-day Saints since its founding in 1830. The study takes a historical stance in discussing the relationship between American public perceptions and the Church\u27s developing internal identity, tracing these changes through three distinct historical stages. Building on the works of historians and sociologists such as Jan Shipps, Armand Mauss, and Terryl Givens, this study hopes to contribute to the understanding of new religious movements and the progression from sect to church.
The study finds that Mormon identity and American perceptions of Mormons have had an inter-influential relationship, each responding and re-forming in turn. The LDS Church has progressed from sect to church as tensions with the host society have lessened. Currently, the Church is at an optimum level of tension with the host society, maintaining a distinct identity while enjoying conventional acceptance
An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
176P/LINEAR is a member of the new cometary class known as main-belt comets
(MBCs). It displayed cometary activity shortly during its 2005 perihelion
passage that may be driven by the sublimation of sub-surface ices. We have
therefore searched for emission of the H2O 110-101 ground state rotational line
at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory on UT 8.78 August 2011,
about 40 days after its most recent perihelion passage, when the object was at
a heliocentric distance of 2.58 AU. No H2O line emission was detected in our
observations, from which we derive sensitive 3-sigma upper limits for the water
production rate and column density of < 4e25 molec/s and of < 3e10 cm^{-2},
respectively. From the peak brightness measured during the object's active
period in 2005, this upper limit is lower than predicted by the relation
between production rates and visual magnitudes observed for a sample of comets
by Jorda et al. (2008) at this heliocentric distance. Thus, 176P/LINEAR was
likely less active at the time of our observation than during its previous
perihelion passage. The retrieved upper limit is lower than most values derived
for the H2O production rate from the spectroscopic search for CN emission in
MBCs.Comment: 5 pages, 2 figures. Minor changes to match published versio
Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN and HNC isotopologues
The 15N isotopologue abundance ratio measured today in different bodies of
the solar system is thought to be connected to 15N-fractionation effects that
would have occured in the protosolar nebula. The present study aims at putting
constraints on the degree of 15N-fractionation that occurs during the
prestellar phase, through observations of D, 13C and 15N-substituted
isotopologues towards B1b. Both molecules from the nitrogen hydride family,
i.e. N2H+ and NH3, and from the nitrile family, i.e. HCN, HNC and CN, are
considered in the analysis. As a first step, we model the continuum emission in
order to derive the physical structure of the cloud, i.e. gas temperature and
H2 density. These parameters are subsequently used as an input in a non-local
radiative transfer model to infer the radial abundances profiles of the various
molecules. Our modeling shows that all the molecules are affected by depletion
onto dust grains, in the region that encompasses the B1-bS and B1-bN cores.
While high levels of deuterium fractionation are derived, we conclude that no
fractionation occurs in the case of the nitrogen chemistry. Independently of
the chemical family, the molecular abundances are consistent with 14N/15N~300,
a value representative of the elemental atomic abundances of the parental gas.
The inefficiency of the 15N-fractionation effects in the B1b region can be
linked to the relatively high gas temperature ~17K which is representative of
the innermost part of the cloud. Since this region shows signs of depletion
onto dust grains, we can not exclude the possibility that the molecules were
previously enriched in 15N, earlier in the B1b history, and that such an
enrichment could have been incorporated into the ice mantles. It is thus
necessary to repeat this kind of study in colder sources to test such a
possibility.Comment: accepted in A&
Mechanistic aspects of thioflavin-T self-aggregation and DNA binding: evidence for dimer attack on DNA grooves
Thioflavin-T (TFT) is a fluorescent marker widely employed in biomedical research but the mechanism of
its binding to polynucleotides has been poorly understood. This paper presents a study of the mechanisms
of TFT self-aggregation and binding to DNA. Relaxation kinetics of TFT solutions show that the cyanine
undergoes dimerization followed by dimer isomerisation. The interaction of TFT with DNA has been
investigated using static methods, such as spectrophotometric and spectrofluorometric titrations under
different conditions (salt content, temperature), fluorescence quenching, viscometric experiments and the
T-jump relaxation method. The combined use of these techniques enabled us to show that the TFT
monomer undergoes intercalation between the DNA base pairs and external binding according to a
branched mechanism. Moreover, it has also been observed that, under dye excess conditions, the TFT
dimer binds to the DNA grooves. The molecular structures of intercalated TFT and the groove-bound
TFT dimer are obtained by performing QM/MM MD simulations
Radio observations of comet 9P/Tempel 1 with the Australia Telescope facilities during the Deep Impact encounter
We present radio observations of comet 9P/Tempel 1 associated with the Deep
Impact spacecraft collision of 2005 July 4. Weak 18-cm OH emission was detected
with the Parkes 64-m telescope, in data averaged over July 4 to 6, at a level
of 12 +/- 3 mJy km/s, corresponding to OH production rate 2.8 x 10^{28}
molecules/second (Despois et al. inversion model, or 1.0 x 10^{28} /s for the
Schleicher & A'Hearn model). We did not detect the HCN 1-0 line with the Mopra
22-m telescope over the period July 2 to 6. The 3 sigma limit of 0.06 K km/s
for HCN on July 4 after the impact gives the limit to the HCN production rate
of < 1.8 x 10^{25} /s. We did not detect the HCN 1-0 line, 6.7 GHz CH_3OH line
or 3.4-mm continuum with the Australia Telescope Compact Array (ATCA) on July
4, giving further limits on any small-scale structure due to an outburst. The 3
sigma limit on HCN emission of 2.5 K km/s from the ATCA around impact
corresponds to limit < 4 x 10^{29} HCN molecules released by the impact.Comment: 7 pages, 1 figure, accepted by MNRA
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
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