54 research outputs found
Introduction to the GiNaC Framework for Symbolic Computation within the C++ Programming Language
The traditional split-up into a low level language and a high level language
in the design of computer algebra systems may become obsolete with the advent
of more versatile computer languages. We describe GiNaC, a special-purpose
system that deliberately denies the need for such a distinction. It is entirely
written in C++ and the user can interact with it directly in that language. It
was designed to provide efficient handling of multivariate polynomials,
algebras and special functions that are needed for loop calculations in
theoretical quantum field theory. It also bears some potential to become a more
general purpose symbolic package
Introduction to XLOOPS
The program package XLOOPS calculates massive one- and two-loop Feynman
diagrams. It consists of five parts:
i) a graphical user interface
ii) routines for generating diagrams from particle input
iii) procedures for calculating one-loop integrals both analytically and
numerically
iv) routines for massive two-loop integrals
v) programs for numerical integration of two-loop diagrams. The package
relies on the application of parallel space techniques. The treatment of tensor
structure and the separation of UV and IR divergences in analytic expressions
is described in this scheme. All analytic calculations are performed with
MAPLE. Two-loop examples taken from Standard Model calculations are presented.
The method has recently been extended to all two-loop vertex topologies,
including the crossed topology, graphs with divergent subloops and IR divergent
diagrams. This will be included in the XLOOPS package in the near future.Comment: 30 pages, LaTeX, uses epsfi
A companion candidate in the gap of the T Cha transitional disk
T Cha is a young star surrounded by a cold disk. The presence of a gap within
its disk, inferred from fitting to the spectral energy distribution, has
suggested on-going planetary formation. We observed T Cha in L' and K_s with
NAOS-CONICA, the adaptive optics system at the VLT, using sparse aperture
masking. We detected a source in the L' data at a separation of 62+-7 mas,
position angle of 78+-1 degrees, and a contrast of delta L' = 5.1+-0.2 mag. The
object is not detected in the Ks band data, which show a 3-sigma contrast limit
of 5.2 mag at the position of the detected L' source. For a distance of 108 pc,
the detected companion candidate is located at 6.7 AU from the primary, well
within the disk gap. If T Cha and the companion candidate are bound, the
comparison of the L' and Ks photometry with evolutionary tracks shows that the
photometry is inconsistent with any unextincted photosphere at the age and
distance of T Cha. The detected object shows a very red Ks-L' color for which a
possible explanation would be a significant amount of dust around it. This
would imply that the companion candidate is young, which would strengthen the
case for a physical companion, and moreover that the object would be in the
substellar regime, according to the Ks upper limit. Another exciting
possibility would be that this companion is a recently formed planet within the
disk. Additional observations are mandatory to confirm that the object is bound
and to properly characterize it.Comment: 4 pages, 4 figures; accepted for publication by A&
Variability of the transitional T Tauri star T Chamaeleontis
We characterize the physical properties of T Chamaeleontis, a transitional T
Tauri star showing UX Ori-type variability, and of its associated disc, and
probe possible effects of disc clearing processes. Different spectral
diagnostics are examined, based on a rich collection of optical high- and
low-resolution spectra. We determine radial and projected rotational
velocities, and measure equivalent widths of the Li I (6708 A) line and of the
most prominent emission lines (e.g. Ha, Hb and [OI] 6300A); we analyse shape
changes of photospheric lines via bisector-method, while variability in Ha and
Hb is inspected through line-profile correlation matrices. The strength of the
Ha and Hb emission is highly variable and well correlated with that of the [OI]
lines, as well as with Av variations of over three magnitudes. Variations up to
nearly 10 km/s in the radial velocity of the star are measured on analogous
time-scale, but with no apparent periodicity. SED modelling confirms the
existence of a gap in the disc. Variable circumstellar extinction is pointed
out as responsible for the conspicuous variations observed in the stellar
continuum flux and for concomitant changes in the emission features by contrast
effect. Clumpy structures, incorporating large dust grains and orbiting the
star within a few tenths of AU, obscure episodically the star and, eventually,
part of the inner circumstellar zone, while the bulk of the hydrogen lines
emitting zone and outer low-density wind region traced by the [OI] remain
unaffected. Coherently with this scenario, the detected radial velocity changes
are also explainable in terms of clumpy materials transiting and partially
obscuring the star.Comment: 38 pages, 32 figures. To appear in the Astronomy and Astrophysics
main journa
Opioid-induced inhibition of the human 5-HT and noradrenaline transporters in vitro: link to clinical reports of serotonin syndrome
Opioids may inhibit the 5-HT transporter (SERT) and the noradrenaline transporter (NET). NET inhibition may contribute to analgesia, and SERT inhibition or interactions with 5-HT receptors may cause serotonergic toxicity. However, the effects of different opioids on the human SERT, NET and 5-HT receptors have not been sufficiently studied.; We determined the potencies of different opioids to inhibit the SERT and NET in vitro using human transporter-transfected HEK293 cells. We also tested binding affinities at 5-HT; 1A; , 5-HT; 2A; and 5-HT; 2C; receptors. Additionally, we assessed clinical cases of the serotonin syndrome associated with each opioid reported by PubMed and a World Health Organization database.; Dextromethorphan, l(R)-methadone, racemic methadone, pethidine, tramadol and tapentadol inhibited the SERT at or close to observed drug plasma or estimated brain concentrations in patients. Tapentadol was the most potent NET inhibitor. Pethidine, tramadol, l(R)-methadone, racemic methadone, dextromethorphan and O-desmethyltramadol also inhibited the NET. 6-Monoacetylmorphine, buprenorphine, codeine, dihydrocodeine, heroin, hydrocodone, hydromorphone, morphine, oxycodone and oxymorphone did not inhibit the SERT or NET. Fentanyl interacted with 5-HT; 1A; receptors and methadone, pethidine and fentanyl with 5-HT; 2A; receptors, in the low micromolar range. Opioids most frequently associated with the serotonin syndrome are tramadol, fentanyl, tapentadol, oxycodone, methadone and dextromethorphan.; Some synthetic opioids interact with the SERT and NET at potentially clinically relevant concentrations. SERT inhibition by tramadol, tapentadol, methadone, dextromethorphan and pethidine may contribute to the serotonin syndrome. Direct effects on 5-HT; 1A; and/or 5-HT; 2A; receptors could be involved with methadone and pethidine
Computer-algebraische und analytische Methoden zur Berechnung von Vertexfunktionen im Standardmodell
Das Standardmodell der elektroschwachen Wechselwirkung hatin den vergangenen Jahrzehnten beachtliche Erfolge erzielt.Die Suche nac
Hyperbolicity, CAT(−1)-spaces and the Ptolemy inequality
Using a four points inequality for the boundary of CAT(−1)-spaces we study the relation between Gromov hyperbolic spaces and CAT(−1)-spaces
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