10,007 research outputs found
Regularity estimates up to the boundary for elliptic systems of difference equations
Regularity estimates up to the boundary for solutions of elliptic systems of finite difference equations were proved. The regularity estimates, obtained for boundary fitted coordinate systems on domains with smooth boundary, involve discrete Sobolev norms and are proved using pseudo-difference operators to treat systems with variable coefficients. The elliptic systems of difference equations and the boundary conditions which are considered are very general in form. The regularity of a regular elliptic system of difference equations was proved equivalent to the nonexistence of eigensolutions. The regularity estimates obtained are analogous to those in the theory of elliptic systems of partial differential equations, and to the results of Gustafsson, Kreiss, and Sundstrom (1972) and others for hyperbolic difference equations
Manganese carbonyl-mediated reactions of azabutadienes with phenylacetylene, methyl acrylate and other unsaturated molecules
Reaction of PhCH₂Mn(CO)₅ with l,4-di-aryl-1-aza-1,3-butadienes gave substituted pyrrolinonyl rings which were η⁴-coordinated to a Mn(CO)₃ group. These are formed by intramolecular CO insertion into a (non-isolated) cyclomanganated intermediate, followed by cyclisation. Other unsaturated reagents (PhC≡CH, CH2=CHCOOMe, PhNCO) gave products arising from insertion of these, including a structurally characterised tri-aryl-η⁵-azacyclohexadienyl-Mn(CO)₃ complex from the reaction with the alkyne.
PhCH₂Mn(CO)₅ reacts with l,4-di-aryl-1-aza-1,3-butadienes in the presence of unsaturated substrates to give products based on a cyclomanganated intermediate
Maternal-Zygotic Epistasis and the Evolution of Genetic Diseases
Many birth defects and genetic diseases are expressed in individuals that do not carry the disease causing alleles. Genetic diseases observed in offspring can be caused by gene expression in mothers and by interactions between gene expression in mothers and offspring. It is not clear whether the underlying pattern of gene expression (maternal versus offspring) affects the incidence of genetic disease. Here we develop a 2-locus population genetic model with epistatic interactions between a maternal gene and a zygotic gene to address this question. We show that maternal effect genes that affect disease susceptibility in offspring persist longer and at higher frequencies in a population than offspring genes with the same effects. We find that specific forms of maternal-zygotic epistasis can maintain disease causing alleles at high frequencies over a range of plausible values. Our findings suggest that the strength and form of epistasis and the underlying pattern of gene expression may greatly influence the prevalence of human genetic diseases
A Vibrio cholerae Classical TcpA Amino Acid Sequence Induces Protective Antibody That Binds an Area Hypothesized To Be Important for Toxin-Coregulated Pilus Structure
Vibrio cholerae is a gram-negative bacterium that has been associated with cholera pandemics since the early 1800s. Whole-cell, killed, and live-attenuated oral cholera vaccines are in use. We and others have focused on the development of a subunit cholera vaccine that features standardized epitopes from various V. cholerae macromolecules that are known to induce protective antibody responses. TcpA protein is assembled into toxin-coregulated pilus (TCP), a type IVb pilus required for V. cholerae colonization, and thus is a strong candidate for a cholera subunit vaccine. Polypeptides (24 to 26 amino acids) in TcpA that can induce protective antibody responses have been reported, but further characterization of their amino acid targets relative to tertiary or quaternary TCP structures has not been done. We report a refinement of the TcpA sequences that can induce protective antibody. One sequence, TcpA 15 (residues 170 to 183), induces antibodies that bind linear TcpA in a Western blot as well as weakly bind soluble TcpA in solution. These antibodies bind assembled pili at high density and provide 80 to 100% protection in the infant mouse protection assay. This is in sharp contrast to other anti-TcpA peptide sera (TcpA 11, TcpA 13, and TcpA 17) that bind very strongly in Western blot and solution assays yet do not provide protection or effectively bind TCP, as evidenced by immunoelectron microscopy. The sequences of TcpA 15 that induce protective antibody were localized on a model of assembled TCP. These sequences are centered on a site that is predicted to be important for TCP structure
Weak magnetic fields in white dwarfs and their direct progenitors?
We have carried out a re-analysis of polarimetric data of central stars of
planetary nebulae, hot subdwarfs, and white dwarfs taken with FORS1 (FOcal
Reducer and low dispersion Spectrograph) on the VLT (Very Large Telescope), and
added a large number of new observations in order to increase the sample. A
careful analysis of the observations using only one wavelength calibration for
the polarimetrically analysed spectra and for all positions of the retarder
plate of the spectrograph is crucial in order to avoid spurious signals. We
find that the previous detections of magnetic fields in subdwarfs and central
stars could not be confirmed while about 10% of the observed white dwarfs have
magnetic fields at the kilogauss level.Comment: 6 pages, Proceedings of the 18th European White Dwarf Workshop, ASP
Conference Serie
A nitrogen model for European catchments: INCA, new model structure and equations
International audienceA new version of the Integrated Nitrogen in Catchments model (INCA) was developed and tested using flow and streamwater nitrate concentration data collected from the River Kennet during 1998. INCA is a process-based model of the nitrogen cycle in the plant/soil and in-stream systems. The model simulates the nitrogen export from different land-use types within a river system, and the in-stream nitrate and ammonium concentrations at a daily time-step. The structure of the new version differs from the original, in that soil-water retention volumes have been added and the interface adapted to permit multiple crop and vegetation growth periods and fertiliser applications. The process equations are now written in terms of loads rather than concentrations allowing a more robust tracking of mass conservation when using numerical integration. The new version is able to reproduce the seasonal dynamics observed in the streamwater nitrogen concentration data, and the loads associated with plant/soil system nitrogen processes reported in the literature. As such, the model results suggest that the new structure is appropriate for the simulation of nitrogen in the River Kennet and an improvement on the original model. The utility of the INCA model is discussed in terms of improving scientific understanding and catchment management. Keywords: modelling, water quality, nitrogen, nitrate, River Kennet, River Thames</p
Discovery of the magnetic field of the B1/B2V star \sigma Lupi
In our search for new magnetic massive stars we use the strongest indirect
indicator of a magnetic field in B stars, which is periodic variability of UV
stellar wind lines occurring in a velocity range symmetric around zero. Our aim
is to obtain follow-up spectropolarimetry to search for a magnetic field in
magnetic candidate stars. We quantify UV wind line variability, and analyse its
time behaviour. The B1/B2V star sigma Lup emerged as a new magnetic candidate
star. AAT spectropolarimetric measurements with SEMPOL were obtained.
The stellar wind line variations of sigma Lup are similar to what is known in
magnetic B stars, but no periodicity could be determined. We detected a
longitudinal magnetic field with varying strength and amplitude of about 100 G
with error bars of typically 20 G, which supports an oblique magnetic-rotator
configuration. The equivalent width variations of the UV lines, the magnetic
and the optical line variations are consistent with the well-known photometric
period of 3.02 days, which we identify with the rotation period of the star.
Additional observations with ESPaDOnS at CFHT strongly confirmed this
discovery, and allowed to determine a precise magnetic period. Further analysis
revealed that Lupi is a helium-strong star, with an enhanced nitrogen
abundance and an underabundance of carbon, and has a spotted surface.
We conclude that sigma Lup is a magnetic oblique rotator, and is a He-strong
star. It is the 4th B star for which a magnetic field is discovered from
studying only its wind variability. Like in the other magnetic B stars the wind
emission originates in the magnetic equator, with maximum emission occurring
when a magnetic pole points towards the Earth. The 3.02 d magnetic rotation
period is consistent with the photometric period, with maximum light
corresponding to maximum magnetic field. A full paper will be submitted to A&A.Comment: 4 pages, 5 figures, to appear in proceedings with AIP. Stellar
polarimetry: From birth to death, Eds. Jennifer Hoffman, Barb Whitney, and
Jon Bjorkma
Improving LIGO calibration accuracy by tracking and compensating for slow temporal variations
Calibration of the second-generation LIGO interferometric gravitational-wave
detectors employs a method that uses injected periodic modulations to track and
compensate for slow temporal variations in the differential length response of
the instruments. These detectors utilize feedback control loops to maintain
resonance conditions by suppressing differential arm length variations. We
describe how the sensing and actuation functions of these servo loops are
parameterized and how the slow variations in these parameters are quantified
using the injected modulations. We report the results of applying this method
to the LIGO detectors and show that it significantly reduces systematic errors
in their calibrated outputs.Comment: 13 pages, 8 figures. This is an author-created, un-copyedited version
of an article published in Classical and Quantum Gravity. IOP Publishing Ltd
is not responsible for any errors or omissions in this version of the
manuscript or any version derived from i
Investigation of the magnetic field characteristics of Herbig Ae/Be stars: Discovery of the pre-main sequence progenitors of the magnetic Ap/Bp stars
We are investigating the magnetic characteristics of pre-main sequence Herbig
Ae/Be stars, with the aim of (1) understanding the origin and evolution of
magnetism in intermediate-mass stars, and (2) exploring the influence of
magnetic fields on accretion, rotation and mass-loss at the early stages of
evolution of A, B and O stars. We have begun by conducting 2 large surveys of
Herbig Ae/Be stars, searching for direct evidence of photospheric magnetic
fields via the longitudinal Zeeman effect. From observations obtained using
FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, we
report the confirmed detection of magnetic fields in 4 pre-main sequence A- and
B-type stars, and the apparent (but as yet unconfirmed) detection of fields in
2 other such stars. We do not confirm the detection of magnetic fields in
several stars reported by other authors to be magnetic: HD 139614, HD 144432 or
HD 31649. One of the most evolved stars in the detected sample, HD 72106A,
shows clear evidence of strong photospheric chemical peculiarity, whereas many
of the other (less evolved) stars do not. The magnetic fields that we detect
appear to have surface intensities of order 1 kG, seem to be structured on
global scales, and appear in about 10% of the stars studied. Based on these
properties, these magnetic stars appear to be pre-main sequence progenitors of
the magnetic Ap/Bp stars.Comment: v2: Include comment regarding publication source To appear in the
proceedings of "Solar Polarisation 4", held in Boulder, USA, Sept. 200
Persistence of self-injury, aggression and property destruction in children and adults with tuberous sclerosis complex
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