147 research outputs found
Methanolysis (solvolysis) And Synthesis Of 4′'-substituted 4-benzyloxybenzyl Chlorides And Some Related Compounds: Comparisons With The Corresponding Benzoyl Compounds
The kinetics of methanolysis (solvolysis) in 97.4% MeOH-dioxan of a series of 4′-substituted 4-benzyloxybenzyl chlorides, and of 4-anisyl, 4-phenoxybenzyl, and benzyl chlorides have been studied and discussed, including comparisons with the data for the corresponding series of benzoyl chlorides, previously reported by us. The 4′-substituted precursor alcohols, chlorides, and product methyl ethers are all new compounds. 4-Anisyl chloride and the series of benzyloxybenzyl chlorides react by the SN1 mechanism, whereas benzyl chloride reacts by the SN2 mechanism. 4-Phenoxybenzyl chloride shows intermediate behaviour. A similar pattern was observed with the corresponding benzoyl compounds. In both series the reactivity order is CH3O > 4′-CH3C6H 4CH2O (-0.76) >C5H5CH 2O (-0.74) > 4′-ClC6H4CH2O (-0.69) > 4′-NO2C6H4CH2O (-0.60) > C6H5O > H (values in parentheses are new σ+ values). At 25° the overall range of rates is 4 290 in the benzyl series, compared with only 2.42 in the benzyl series. The Arrhenius parameters in the two series demonstrate, however, an underlying similarity with obvious differences superimposed. In both series, the introduction of 4-OR groups leads to a ΔS‡ increase of ca. 40 J mol-1 K -1. In the benzyl series this is accompanied by ΔE‡ decreases of ca. 6-10 kJ mol-1, whereas in the benzoyl series ΔE‡ values increase by ca. 10-15 kJ mol-1. The equation log k = log k0 + n[MeOH] in mixtures with increasing content of dioxan, was used to study the rate dependence on MeOH concentration. Values of n are ca. 5 between 97.4 and 8.3.% MeOH, and ca. 3 between 83.3 and 50.0% MeOH.110010
Note on Triangle Anomalies and Assignment of Singlet in 331-like Model
It is pointed out that in the like model which uses both fundamental
and complex conjugate representations for an assignment of the representations
to the left-handed quarks and the scalar representation to their corresponding
right-handed counterparts, the nature of the scalar should be taken into
account in order to make the fermion triangle anomalies in the theory
anomaly-free, i.e. renormalizable in a sense with no anomalies, even after the
spontaneous symmetry breaking.Comment: 8 page no figures, acknowledgments adde
Photodetachment study of He^- quartet resonances below the He(n=3) thresholds
The photodetachment cross section of He^- has been measured in the photon
energy range 2.9 eV to 3.3 eV in order to investigate doubly excited states.
Measurements were made channel specific by selectively detecting the residual
He atoms left in a particular excited state following detachment. Three
Feshbach resonances were found in the He(1s2p ^3P)+e^-(epsilon p) partial cross
section: a ^4S resonance below the He(1s3s ^3S) threshold and two ^4P
resonances below the He(1s3p ^3P) threshold. The measured energies of these
doubly excited states are 2.959260(6) eV, 3.072(7) eV and 3.26487(4) eV. The
corresponding widths are found to be 0.20(2) meV, 50(5) meV and 0.61(5) meV.
The measured energies agree well with recent theoretical predictions for the
1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P states, respectively, but the widths
deviate noticeably from calculations for 1s3p^2 ^4P and 1s3p4p ^4P states.Comment: 10 pages, 3 figures, LaTeX2e scrartcl, amsmath. Accepted by Journal
of Physics B; minor changes after referee repor
Stream Members Only: Data-Driven Characterization of Stellar Streams with Mixture Density Networks
Stellar streams are sensitive probes of the Milky Way's gravitational
potential. The mean track of a stream constrains global properties of the
potential, while its fine-grained surface density constrains galactic
substructure. A precise characterization of streams from potentially noisy data
marks a crucial step in inferring galactic structure, including the dark
matter, across orders of magnitude in mass scales. Here we present a new method
for constructing a smooth probability density model of stellar streams using
all of the available astrometric and photometric data. To characterize a
stream's morphology and kinematics, we utilize mixture density networks to
represent its on-sky track, width, stellar number density, and kinematic
distribution. We model the photometry for each stream as a single-stellar
population, with a distance track that is simultaneously estimated from the
stream's inferred distance modulus (using photometry) and parallax distribution
(using astrometry). We use normalizing flows to characterize the distribution
of background stars. We apply the method to the stream GD-1, and the tidal
tails of Palomar 5. For both streams we obtain a catalog of stellar membership
probabilities that are made publicly available. Importantly, our model is
capable of handling data with incomplete phase-space observations, making our
method applicable to the growing census of Milky Way stellar streams. When
applied to a population of streams, the resulting membership probabilities from
our model form the required input to infer the Milky Way's dark matter
distribution from the scale of the stellar halo down to subhalos.Comment: 35 pages, 13 figures, 4 tables, fully open-source and reproducible
using ShowYourWor
Comparison Of Methanolysis Of A Series Of P-benzyloxybenzoyl Chlorides With That Of Benzoyl, P-phenoxybenzoyl, And P-methoxybenzoyl Chlorides
The kinetics of the methanolysis (solvolysis) of a series of p-benzyloxybenzoyl chlorides have been compared with values for benzoyl, p-methoxybenzoyl. and p-phenoxybenzoyl chloride. Small rate differences between benzoyl chloride and the other compounds stem from counterbalancing large changes in enthalpies and entropies of activation, ascribed to different degrees of SN1 character in the reactions. Differences within the benzyloxy-series are ascribed to effects of substituents on the inductive effect of the benzene ring of the benzyloxy-group. Data have been analysed in terms of the Hammett equation. Values of σ for the p-benzyloxy-group were obtained from both kinetic and acidity measurements : both are considerably less than the literature value, which we regard as suspect. A coefficient of transmission of electronic effects across a p-benzyloxy-group was determined as 0.17.141648165
Stat1 nuclear translocation by nucleolin upon monocyte differentiation
BACKGROUND: Members of the signal transducer and activator of transcription (Stat) family of transcription factors traverse the nuclear membrane through a specialized structure, called the nuclear pore complex (NPC), which represents a selective filter for the import of proteins. Karyophilic molecules can bind directly to a subset of proteins of the NPC, collectively called nucleoporins. Alternatively, the transport is mediated via a carrier molecule belonging to the importin/karyopherin superfamily, which transmits the import into the nucleus through the NPC. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we provide evidence for an alternative Stat1 nuclear import mechanism, which is mediated by the shuttle protein nucleolin. We observed Stat1-nucleolin association, nuclear translocation and specific binding to the regulatory DNA element GAS. Using expression of nucleolin transgenes, we found that the nuclear localization signal (NLS) of nucleolin is responsible for Stat1 nuclear translocation. We show that this mechanism is utilized upon differentiation of myeloid cells and is specific for the differentiation step from monocytes to macrophages. CONCLUSIONS/SIGNIFICANCE: Our data add the nucleolin-Stat1 complex as a novel functional partner for the cell differentiation program, which is uniquely poised to regulate the transcription machinery via Stat1 and nuclear metabolism via nucleolin
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External Galaxies with the Nancy Grace Roman Space Telescope
Stellar streams form through the tidal disruption of satellite galaxies or
globular clusters orbiting a host galaxy. Globular cluster streams are exciting
since they are thin (dynamically cold) and, therefore sensitive to
perturbations from low-mass subhalos. Since the subhalo mass function differs
depending on the dark matter composition, these gaps can provide unique
constraints on dark matter models. However, current samples are limited to the
Milky Way. With its large field of view, deep imaging sensitivity, and high
angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and
gaps significantly. This paper presents a first exploration of the prospects
for detecting gaps in streams in M31 and other nearby galaxies with resolved
stars. We simulate the formation of gaps in a Palomar-5-like stream and
generate mock observations of these gaps with background stars in M31 and the
foreground Milky Way stellar fields. We assess Roman's ability to detect gaps
out to 10 Mpc through visual inspection and with the gap-finding tool
. We conclude that gaps of kpc in streams
that are created from subhalos of masses M are
detectable within a 2-3 Mpc volume in exposures of 1000s to 1 hour. This volume
contains galaxies, including galaxies with
luminosities L. Large samples of stream gaps in external
galaxies will open up a new era of statistical analyses of gap characteristics
in stellar streams and help constrain dark matter models.Comment: ApJ versio
Photodetachment study of the 1s3s4s ^4S resonance in He^-
A Feshbach resonance associated with the 1s3s4s ^{4}S state of He^{-} has
been observed in the He(1s2s ^{3}S) + e^- (\epsilon s) partial photodetachment
cross section. The residual He(1s2s ^{3}S) atoms were resonantly ionized and
the resulting He^+ ions were detected in the presence of a small background. A
collinear laser-ion beam apparatus was used to attain both high resolution and
sensitivity. We measured a resonance energy E_r = 2.959 255(7) eV and a width
\Gamma = 0.19(3) meV, in agreement with a recent calculation.Comment: LaTeX article, 4 pages, 3 figures, 21 reference
Electron affinity of Li: A state-selective measurement
We have investigated the threshold of photodetachment of Li^- leading to the
formation of the residual Li atom in the state. The excited residual
atom was selectively photoionized via an intermediate Rydberg state and the
resulting Li^+ ion was detected. A collinear laser-ion beam geometry enabled
both high resolution and sensitivity to be attained. We have demonstrated the
potential of this state selective photodetachment spectroscopic method by
improving the accuracy of Li electron affinity measurements an order of
magnitude. From a fit to the Wigner law in the threshold region, we obtained a
Li electron affinity of 0.618 049(20) eV.Comment: 5 pages,6 figures,22 reference
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