42,850 research outputs found
Multi-epoch infrared photometry of the star forming region G173.58+2.45
We present a multi-epoch infrared photometric study of the intermediate-mass
star forming region G173.58+2.45. Photometric observations are obtained using
the near-infrared filters and narrow-band filters centered at the
wavelengths of H (1-0) S(1) (2.122 m) and [FeII] (1.644 m) lines.
The H image shows molecular emission from shocked gas, implying the
presence of multiple star formation and associated outflow activity. We see
evidence for several collimated outflows. The most extended jet is at least
0.25 pc in length and has a collimation factor of 10, which may be
associated with a binary system within the central cluster, resolved for the
first time here. This outflow is found to be episodic; probably occurring or
getting enhanced during the periastron passage of the binary. We also find that
the variable star in the vicinity of the outflow source, which was known as a
FU Ori type star, is probably not a FU Ori object. However, it does drive a
spectacular outflow and the variability is likely to be related to accretion,
when large clouds of gas and dust spiral in towards the central source. Many
other convincing accretion-outflow systems and YSO candidates are discovered in
the field.Comment: 15 pages, 9 figures, accepted for publication in MNRA
Microscopic resolution broadband dielectric spectroscopy
Results are presented for a non-contact measurement system capable of micron level spatial resolution. It utilises the novel electric potential sensor (EPS) technology, invented at Sussex, to image the electric field above a simple composite dielectric material. EP sensors may be regarded as analogous to a magnetometer and require no adjustments or offsets during either setup or use. The sample consists of a standard glass/epoxy FR4 circuit board, with linear defects machined into the surface by a PCB milling machine. The sample is excited with an a.c. signal over a range of frequencies from 10 kHz to 10 MHz, from the reverse side, by placing it on a conducting sheet connected to the source. The single sensor is raster scanned over the surface at a constant working distance, consistent with the spatial resolution, in order to build up an image of the electric field, with respect to the reference potential. The results demonstrate that both the surface defects and the internal dielectric variations within the composite may be imaged in this way, with good contrast being observed between the glass mat and the epoxy resin
Perturbation Theory of Coulomb Gauge Yang-Mills Theory Within the First Order Formalism
Perturbative Coulomb gauge Yang-Mills theory within the first order formalism
is considered. Using a differential equation technique and dimensional
regularization, analytic results for both the ultraviolet divergent and finite
parts of the two-point functions at one-loop order are derived. It is shown how
the non-ultraviolet divergent parts of the results are finite at spacelike
momenta with kinematical singularities on the light-cone and subsequent branch
cuts extending into the timelike region.Comment: 23 pages, 6 figure
Analytic solutions of the magnetic annihilation and reconnection problems. I. Planar flow profiles
The phenomena of steady-state magnetic annihilation and reconnection in the vicinity of magnetic nulls are considered. It is shown that reconnective solutions can be derived by superposing the velocity and magnetic fields of simple magnetic annihilation models. These solutions contain most of the previous models for magnetic merging and reconnection, as well as introducing several new solutions. The various magnetic dissipation mechanisms are classified by examining the scaling of the Ohmic diffusion rate with plasma resistivity. Reconnection solutions generally allow more favorable "fast" dissipation scalings than annihilation models. In particular, reconnection models involving the advection of planar field components have the potential to satisfy the severe energy release requirements of the solar flare. The present paper is mainly concerned with magnetic fields embedded in strictly planar flows—a discussion of the more complicated three-dimensional flow patterns is presented in Part II [Phys. Plasmas 4, 110 (1997)]
The shape of primordial non-Gaussianity and the CMB bispectrum
We present a set of formalisms for comparing, evolving and constraining
primordial non-Gaussian models through the CMB bispectrum. We describe improved
methods for efficient computation of the full CMB bispectrum for any general
(non-separable) primordial bispectrum, incorporating a flat sky approximation
and a new cubic interpolation. We review all the primordial non-Gaussian models
in the present literature and calculate the CMB bispectrum up to l <2000 for
each different model. This allows us to determine the observational
independence of these models by calculating the cross-correlation of their CMB
bispectra. We are able to identify several distinct classes of primordial
shapes - including equilateral, local, warm, flat and feature (non-scale
invariant) - which should be distinguishable given a significant detection of
CMB non-Gaussianity. We demonstrate that a simple shape correlator provides a
fast and reliable method for determining whether or not CMB shapes are well
correlated. We use an eigenmode decomposition of the primordial shape to
characterise and understand model independence. Finally, we advocate a
standardised normalisation method for based on the shape
autocorrelator, so that observational limits and errors can be consistently
compared for different models.Comment: 32 pages, 20 figure
Primordial non-Gaussianity and the CMB bispectrum
We present a new formalism, together with efficient numerical methods, to
directly calculate the CMB bispectrum today from a given primordial bispectrum
using the full linear radiation transfer functions. Unlike previous analyses
which have assumed simple separable ansatze for the bispectrum, this work
applies to a primordial bispectrum of almost arbitrary functional form, for
which there may have been both horizon-crossing and superhorizon contributions.
We employ adaptive methods on a hierarchical triangular grid and we establish
their accuracy by direct comparison with an exact analytic solution, valid on
large angular scales. We demonstrate that we can calculate the full CMB
bispectrum to greater than 1% precision out to multipoles l<1800 on reasonable
computational timescales. We plot the bispectrum for both the superhorizon
('local') and horizon-crossing ('equilateral') asymptotic limits, illustrating
its oscillatory nature which is analogous to the CMB power spectrum
Gamma-Ray Bursts observed by XMM-Newton
Analysis of observations with XMM-Newton have made a significant contribution
to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area,
bandpass and resolution of the EPIC instrument permit the study of a wide
variety of spectral features. In particular, strong, time-dependent, soft X-ray
emission lines have been discovered in some bursts. The emission mechanism and
energy source for these lines pose major problems for the current generation of
GRB models. Other GRBs have intrinsic absorption, possibly related to the
environment around the progenitor, or possible iron emission lines similar to
those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of
GRBs discovered by the Swift satellite should help unlock the origin of the GRB
phenomenon over the next few years.Comment: To appear in proceedings of the "XMM-Newton EPIC Consortium meeting,
Palermo, 2003 October 14-16", published in Memorie della Societa Astronomica
Italian
Delayed soft X-ray emission lines in the afterglow of GRB 030227
Strong, delayed X-ray line emission is detected in the afterglow of GRB
030227, appearing near the end of the XMM-Newton observation, nearly twenty
hours after the burst. The observed flux in the lines, not simply the
equivalent width, sharply increases from an undetectable level (<1.7e-14
erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line
emission alone has nearly twice as many detected photons as any previous
detection of X-ray lines. The lines correspond well to hydrogen and/or
helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is
no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a
tenth that of the lighter metals. If the supernova and GRB events are nearly
simultaneous there must be continuing, sporadic power output after the GRB of a
luminosity >~5e46 erg/s, exceeding all but the most powerful quasars.Comment: Submitted to ApJL. 14 pages, 3 figures with AASLaTe
Mode of action of local anaesthetics
In conclusion, it is possible to compile a list of salient
features which are obviously important, and most of which
have been fairly clearly proved:1. The theoretical investigation of local anaesthesia and
its practical application are often unrelated. A striking example is the pII effect upon the action of procaine at mucous surfaces.
|| 2. The present widely-accepted views on nerve impulse Iran
smission give added prestige to views on nerve block
being caused bypermeability changes. That many local
anaesthetics stabilize membrane conditions is very noteworthy.
|| 3. That some agents block by depolarization is undeniable,
but since the nerve impulse is accompanied by a wave of
depolarization, it is clear that, if drugs blocked in
this way, their blocking effect would be preceded by
stimulatory effect, and this is not borne out in clinipractice.
|| 4. From studies of conduction it is to be expected that
inhibition. of metabolism may ultimately cause block,
but it is a fairly slow process, due to such factors as the anoxic reserve.
|| 5. Permeability or metabolic effects occur at, or in, the
surface, and this must be partially governed by lipoid
solubility (Overton -Meyer theory) and. also by adsorntion (Warburg theory).
|| 6. Sooner or later the drug penetrates the cell, and the
free base is the agent for achieving this in most local
anaesthetics (of the basic type).
|| 7. Because of this action of the free -base, the pH of the
anaesthetic solution, and the modifying one of the surrounding medium, have an important part to play in the
efficacy of the drug.
|| 8. There is a growing body of evidence that the free base secures penetration into the cell, and that it is then converted into the cation., which is, in fact, the true
'nucleus' of local anaesthetic activity.
|| 9. Considerable variation in activity arises from connective tissue, etc. around the nerve fibres, because of
the impedance it causes to movement of the drug. This,
coupled with site of injection, and pH, may explain
many of the delays in onset of drug action,
|| 10. Myelination provides a further barrier to drug action,
and may explain why drugs take longer to act on medullated nerves, since the drug has to effect an entry at
the nodes of Ranvier first. It effectively ensures the
under normal conditions (of oxygenation, etc.) the un-myelinated fibres (and. this includes the ones carrying
sensations of pain) block first.
|| 11. Farther differentiation is provided by partial blocking
which disrupts some impulse frequencies in nerves,
whilst leaving others unchanged. By virtue of this,
certain intensities of sensation may be selectively
eliminated before others.
|| 12. There is some evidence for preferential local anesthetic effects in the vicinity of the sensory nerve endings, i.e. at the receptor, or immediately adjacent
to it. This might well allow a further differentiation
of effect, especially if some endings are more susceptible than others.
|| 13. The peculiar susceptibility of the nodes of Ranvier to
drug action lends support to the saltatory theory
of nerve conduction, although it is not vital to the
present study
Recommended from our members
Organic geochemistry of the crater-fill sediments from Boltysh impact crater, Ukraine
The Boltysh impact crater, is a complex structure formed on the basement rocks of the Ukrainian shield which has been dated at 65.17±0.64 Ma [1]. The Boltysh crater has been know for several decades and was originally drilled in the 1960s-1980s in a study of economic oil shale deposits. Unfortunately, the cores were not curated and have been lost. However we have recently re-drilled the impact crater and have recovered a near continuous record of ~400 m of organic rich sediments deposited in a deep isolated lake which overlie the basement rocks spanning a period ~10 Ma. At 24km diameter, Boltysh will not have contributed substantially to the worldwide devastation at the end of the
Cretaceous. However, the precise age of the Boltysh impact relative to the Chicxulub impact and its location on a stable low lying coastal plain which allowed formation of the postimpact crater lake make it a particularly important locality. After the impact, the crater quickly filled with water in a short marine phase but returned to fresh water which persisted for >10Ma [2]. These strata contain a valuable record of Paleogene environmental change in central Europe, and one of very few terrestrial records of the KT event. This pre-eminent record of the Paleogene can help us to answer several related scientific questions including the relative age of Boltysh compared with Chicxulub, recovery from the impact, and later climate signals. The organic geochemistry and playnology indicate main inputs to be algal and higher plant within most of the core although there are some marked changes in inputs in some sections. A number of carbon isotope excursions are also present within the core which are currently being further investigated
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