1,154 research outputs found
An ab initio and matrix isolation infrared study of the 1:1 C<SUB>2</SUB>H<SUB>2</SUB>-CHCl<SUB>3</SUB> adduct
The details of weak C-H···π interactions that control several inter and intramolecular structures have been studied experimentally and theoretically for the 1:1 C2H2-CHCl3 adduct. The adduct was generated by depositing acetylene and chloroform in an argon matrix and a 1:1 complex of these species was identified using infrared spectroscopy. Formation of the adduct was evidenced by shifts in the vibrational frequencies compared to C2H2 and CHCl3 species. The molecular structure, vibrational frequencies and stabilization energies of the complex were predicted at the MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels. Both the computational and experimental data indicate that the C2H2-CHCl3 complex has a weak hydrogen bond involving a C-H···π interaction, where the C2H2 acts as a proton acceptor and the CHCl3 as the proton donor. In addition, there also appears to be a secondary interaction between one of the chlorine atoms of CHCl3 and a hydrogen in C2H2. The combination of the C-H···π interaction and the secondary Cl···H interaction determines the structure and the energetics of the C2H2-CHCl3 complex. In addition to the vibrational assignments for the C2H2-CHCl3 complex we have also observed and assigned features owing to the proton accepting C2H2 submolecule in the acetylene dimer
Embeddings of hyperbolic Kac-Moody algebras into }
We show that the rank 10 hyperbolic Kac-Moody algebra contains every
simply laced hyperbolic Kac-Moody algebra as a Lie subalgebra. Our method is
based on an extension of earlier work of Feingold and Nicolai.Comment: 10 pages. to appear in Letters in Mathematical Physic
Pearling and Pinching: Propagation of Rayleigh Instabilities
A new category of front propagation problems is proposed in which a spreading
instability evolves through a singular configuration before saturating. We
examine the nature of this front for the viscous Rayleigh instability of a
column of one fluid immersed in another, using the marginal stability criterion
to estimate the front velocity, front width, and the selected wavelength in
terms of the surface tension and viscosity contrast. Experiments are suggested
on systems that may display this phenomenon, including droplets elongated in
extensional flows, capillary bridges, liquid crystal tethers, and viscoelastic
fluids. The related problem of propagation in Rayleigh-like systems that do not
fission is also considered.Comment: Revtex, 7 pages, 4 ps figs, PR
Twisted Conjugacy Classes in Lattices in Semisimple Lie Groups
Given a group automorphism , one has an action of
on itself by -twisted conjugacy, namely, .
The orbits of this action are called -conjugacy classes. One says that
has the -property if there are infinitely many
-conjugacy classes for every automorphism of . In this
paper we show that any irreducible lattice in a connected semi simple Lie group
having finite centre and rank at least 2 has the -property.Comment: 6 page
The Kodaira dimension of the moduli of K3 surfaces
The moduli space of polarised K3 surfaces of degree 2d is a quasi-projective
variety of dimension 19. For general d very little has been known about the
Kodaira dimension of these varieties. In this paper we present an almost
complete solution to this problem. Our main result says that this moduli space
is of general type for d>61 and for d=46,50,54,58,60.Comment: 47 page
Background and Anomaly Learning Methods for Static Gamma-ray Detectors
Static gamma-ray detector systems that are deployed outdoors for radiological
monitoring purposes experience time- and spatially-varying natural backgrounds
and encounters with man-made nuisance sources. In order to be sensitive to
illicit sources, such systems must be able to distinguish those sources from
benign variations due to, e.g., weather and human activity. In addition to
fluctuations due to non-threats, each detector has its own response and energy
resolution, so providing a large network of detectors with predetermined
background and source templates can be an onerous task. Instead, we propose
that static detectors use simple physics-informed algorithms to automatically
learn the background and nuisance source signatures, which can them be used to
bootstrap and feed into more complex algorithms. Specifically, we show that
non-negative matrix factorization (NMF) can be used to distinguish static
background from the effects of increased concentrations of radon progeny due to
rainfall. We also show that a simple process of using multiple gross count rate
filters can be used in real time to classify or ``triage'' spectra according to
whether they belong to static, rain, or anomalous categories for processing
with other algorithms. If a rain sensor is available, we propose a method to
incorporate that signal as well. Two clustering methods for anomalous spectra
are proposed, one using Kullback-Leibler divergence and the other using
regularized NMF, with the goal of finding clusters of similar spectral
anomalies that can be used to build anomaly templates. Finally we describe the
issues involved in the implementation of some of these algorithms on deployed
sensor nodes, including the need to monitor the background models for long-term
drifting due to physical changes in the environment or changes in detector
performance.Comment: 12 pages, 6 figures, accepted for publication in IEEE Transactions on
Nuclear Scienc
Hiding in plain sight: Tactical concealment as a complex pathway to relational wellbeing
We argue that the current environment in higher education is one of the primary drivers for the widespread adoption of concealment tactics with the aim of enhancing wellbeing. To explore the relationship between concealment and wellbeing, we draw upon Scott’s (1990) conceptualization of ‘hidden transcripts’ and Keyes’s (1998, 2002) five dimensions of social wellbeing. Using a collaborative ethnographic approach, we examine a two-year period of individual and collective inquiry by an eclectic multidisciplinary, international group of academics. Our empirical and theoretical contributions expose a complex and, at times, seemingly contradictory relationship between tactical concealments and relational wellbeing, with variously generative and destructive pathways between them. Our research offers a lens through which we can critically explore and extend our understanding of alternative pathways to wellbeing in organizational life
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Altered translation of GATA1 in Diamond-Blackfan anemia
Ribosomal protein haploinsufficiency occurs in diverse human diseases including Diamond-Blackfan anemia (DBA),1,2 congenital asplenia,3 and T-cell leukemia.4 Yet how mutations in such ubiquitously expressed proteins result in cell-type and tissue specific defects remains a mystery.5 Here, we show that GATA1 mutations that reduce full-length protein levels of this critical hematopoietic transcription factor can cause DBA in rare instances. We show that ribosomal protein haploinsufficiency, the more common cause of DBA, can similarly reduce translation of GATA1 mRNA - a phenomenon that appears to result from this mRNA having a higher threshold for initiation of translation. In primary hematopoietic cells from patients with RPS19 mutations, a transcriptional signature of GATA1 target genes is globally and specifically reduced, confirming that the activity, but not the mRNA level, of GATA1 is reduced in DBA patients with ribosomal protein mutations. The defective hematopoiesis observed in DBA patients with ribosomal protein haploinsufficiency can be at least partially overcome by increasing GATA1 protein levels. Our results provide a paradigm by which selective defects in translation due to mutations in ubiquitous ribosomal proteins can result in human disease
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