6,456 research outputs found
From mass to structure: An aromaticity index for high-resolution mass data of natural organic matter
Recent progress in Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) provided extensive molecular mass data for complex natural organic matter (NOM). Structural information can be deduced solely from the molecular masses for ions with extreme molecular element ratios, in particular low H/C ratios, which are abundant in thermally altered NOM (e.g. black carbon). In this communication we propose a general aromaticity index (AI) and two threshold values as unequivocal criteria for the existence of either aromatic (AI > 0.5) or condensed aromatic structures (AI >= 0.67) in NOM. AI can be calculated from molecular formulae which are derived from exact molecular masses of naturally occurring compounds containing C, H, O, N, S and P and is especially applicable for substances with aromatic cores and few alkylations. In order to test the validity of our model index, AI is applied to FTICRMS data of a NOM deep-water sample from the Weddell Sea (Antarctica), a fulvic acid standard and an artificial dataset of all theoretically possible molecular formulae. For graphical evaluation a ternary plot is suggested for four-dimensional data representation. The proposed aromaticity index is a step towards structural identification of NOM and the molecular identification of black carbon in the environment
Quantum statistics of interacting dimer spin systems
The compound TlCuCl3 represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Wurtz [Phys. Rev. B 50, 13 515 (1994)] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important
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
Time-dependent Ginzburg-Landau equations for mixed d- and s-wave superconductors
A set of coupled time-dependent Ginzburg-Landau equations (TDGL) for
superconductors of mixed d- and s-wave symmetry are derived microscopically
from the Gor'kov equations by using the analytical continuation technique. The
scattering effects due to impurities with both nonmagnetic and magnetic
interactions are considered. We find that the d- and s-wave components of the
order parameter can have very different relaxation times in the presence of
nonmagnetic impurities. This result is contrary to a set of phenomenologically
proposed TDGL equations and thus may lead to new physics in the dynamics of
flux motion.Comment: 22 pages, 6 figures are available upon request, to appear in Phys.
Rev.
Electron transport in strongly disordered structures
Using the transfer matrix technique, we investigate the propagation of
electron through a two dimensional disordered sample. We find that the spatial
distribution of electrons is homogeneous only in the limit of weak disorder
(diffusive transport regime). In the limit of very strong disorder, we identify
a narrow channel through which the electron propagates from one side of the
sample to the opposite side. Even in this limit, we prove the wave character of
the electron propagation.Comment: Presented at ETOPIM
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A simplified explanation for the frameshift mutation that created a novel C-terminal motif in the APETALA3 gene lineage
BACKGROUND: The evolution of type II MADS box genes has been extensively studied in angiosperms. One of the best-understood subfamilies is that of the Arabidopsis gene APETALA3 (AP3). Previous work has demonstrated that the ancestral paleoAP3 lineage was duplicated at some point within the basal eudicots to give rise to the paralogous TM6 and euAP3 lineages. This event was followed in euAP3 orthologs by the replacement of the C-terminal paleoAP3 motif with the derived euAP3 motif. It has been suggested that the new motif was created by an eight-nucleotide insertion that produced a translational frameshift. RESULTS: The addition of 25 eudicot AP3 homologs to the existing dataset has allowed us to clarify the process by which the euAP3 motif evolved. Phylogenetic analysis indicates that the euAP3/TM6 duplication maps very close to the base of the core eudicots, associated with the families Trochodendraceae and Buxaceae. We demonstrate that although the transformation of paleoAP3 into euAP3 was due to a frameshift mutation, this was the result of a single nucleotide deletion. The use of ancestral character state reconstructions has allowed us to demonstrate that the frameshift was accompanied by few other nucleotide changes. We further confirm that the sequence is evolving as coding region. CONCLUSION: This study demonstrates that the simplest of genetic changes can result in the remodeling of protein sequence to produce a kind of molecular 'hopeful monster.' Moreover, such a novel protein motif can become conserved almost immediately on the basis of what appears to be a rapidly generated new function. Given that the existing data on the function of such C-terminal motifs are somewhat disparate and contradictory, we have sought to synthesize previous findings within the context of the current analysis and thereby highlight specific hypotheses that require further investigation before the significance of the euAP3 frameshift event can be fully understood
Constraining the dense matter equation-of-state with radio pulsars
Radio pulsars provide some of the most important constraints for our
understanding of matter at supranuclear densities. So far, these constraints
are mostly given by precision mass measurements of neutron stars (NS). By
combining single measurements of the two most massive pulsars, J03480432 and
J07406620, the resulting lower limit of 1.98 (99% confidence) of
the maximum NS mass, excludes a large number of equations of state (EOSs).
Further EOS constraints, complementary to other methods, are likely to come
from the measurement of the moment of inertia (MOI) of binary pulsars in
relativistic orbits. The Double Pulsar, PSR J07373039A/B, is the most
promising system for the first measurement of the MOI via pulsar timing.
Reviewing this method, based in particular on the first MeerKAT observations of
the Double Pulsar, we provide well-founded projections into the future by
simulating timing observations with MeerKAT and the SKA. For the first time, we
account for the spin-down mass loss in the analysis. Our results suggest that
an MOI measurement with 11% accuracy (68% confidence) is possible by 2030. If
by 2030 the EOS is sufficiently well known, however, we find that the Double
Pulsar will allow for a 7% test of Lense-Thirring precession, or alternatively
provide a -measurement of the next-to-leading order gravitational
wave damping in GR. Finally, we demonstrate that potential new discoveries of
double NS systems with orbital periods shorter than that of the Double Pulsar
promise significant improvements in these measurements and the constraints on
NS matter.Comment: 13 pages, 8 figures. Accepted by MNRA
Comparison in the immunological properties of Borrelia burgdorferi isolates from Ixodes ricinus derived from three endemic areas in Switzerland
Borrelia burgdorferi isolates were obtained from Ixodes ricinus from three sites in Switzerland. They were examined by SDS-PAGE and immunoblotting. The phenotypes, in respect of three outer surface proteins (Osp), differed between the sites of collection. In site 1, most isolates had an OspA of 31 kDa and an OspB of 34 kDa: in site 2, isolates presenting an OspA of 33 kDa dominated and in site 3, the isolates with an OspA of 32 kDa and an OspB of 35 kDa were most frequent. This distribution differed significantly. About half of the isolates from sites 1 and 3 reacted with anti-OspA monoclonal antibody H5332 compared to 29% from site 2. Site 1 isolates reacted significantly more frequently (81 %) with another anti-OspA monoclonal antibody LA-31 than isolates from site 3 (P < 0·0001). These findings have implications for the epidemiology of Lyme borreliosis, for the further development of serodiagnostic reagents and for the development of a vaccin
Upper bounds on the size of 4- and 6-cycle-free subgraphs of the hypercube
In this paper we modify slightly Razborov's flag algebra machinery to be
suitable for the hypercube. We use this modified method to show that the
maximum number of edges of a 4-cycle-free subgraph of the n-dimensional
hypercube is at most 0.6068 times the number of its edges. We also improve the
upper bound on the number of edges for 6-cycle-free subgraphs of the
n-dimensional hypercube from the square root of 2 - 1 to 0.3755 times the
number of its edges. Additionally, we show that if the n-dimensional hypercube
is considered as a poset, then the maximum vertex density of three middle
layers in an induced subgraph without 4-cycles is at most 2.15121 times n
choose n/2.Comment: 14 pages, 9 figure
Gravitational signal propagation in the double pulsar studied with the MeerKAT telescope
The double pulsar PSR J0737−3039A/B has offered a wealth of gravitational experiments in the strong-field regime, all of which
general relativity has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the
double pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in the future, the Square Kilometre Array
(SKA) can greatly improve the accuracy of current tests and facilitate tests of next-to-leading-order (NLO) contributions in both
orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737−3039A, made using the
MeerKAT telescope over the last three years. The increased timing precision offered by MeerKAT yields a measurement of Shapiro
delay parameter s that it twice as good, and an improved mass measurements compared to previous studies. In addition, our results
provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16 yr
data by a factor of 1.65. These effects include the retardation effect due to the movement of the companion and the deflection of
the signal by the gravitational field of the companion. We also investigate the novel effects that have been expected. For instance, we
search for potential profile variations near superior conjunctions caused by shifts of the line of sight due to latitudinal signal deflection,
and we find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to
be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the
expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally,
we provide an improved analytical description for the signal propagation in the double pulsar system that meets the timing precision
expected from future instruments such as the full SKA
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