5,493 research outputs found
Prognostic and therapeutic significance of carbohydrate antigen 19-9 as tumor marker in patients with pancreatic cancer
In pancreatic cancer ( PC) accurate determination of treatment response by imaging often remains difficult. Various efforts have been undertaken to investigate new factors which may serve as more appropriate surrogate parameters of treatment efficacy. This review focuses on the role of carbohydrate antigen 19- 9 ( CA 19- 9) as a prognostic tumor marker in PC and summarizes its contribution to monitoring treatment efficacy. We undertook a Medline/ PubMed literature search to identify relevant trials that had analyzed the prognostic impact of CA 19- 9 in patients treated with surgery, chemoradiotherapy and chemotherapy for PC. Additionally, relevant abstract publications from scientific meetings were included. In advanced PC, pretreatment CA 19- 9 levels have a prognostic impact regarding overall survival. Also a CA 19- 9 decline under chemotherapy can provide prognostic information for median survival. A 20% reduction of CA 19- 9 baseline levels within the first 8 weeks of chemotherapy appears to be sufficient to define a prognostic relevant subgroup of patients ('CA 19- 9 responder'). It still remains to be defined whether the CA 19- 9 response is a more reliable method for evaluating treatment efficacy compared to conventional imaging. Copyright (c) 2006 S. Karger AG, Basel
Magneto-centrifugally driven winds: comparison of MHD simulations with theory
Stationary magnetohydrodynamic (MHD) outflows from a rotating, conducting
Keplerian accretion disk threaded by B-field are investigated numerically by
time-dependent, axisymmetric (2.5D) simulations using a Godunov-type code. A
large class of stationary magneto-centrifugally driven winds are found where
matter is accelerated from a thermal speed at the disk to much larger velocity,
greater than the fast magnetosonic speed and larger than the escape speed. The
flows are approximately spherical outflows with only small collimation within
the simulation region. Numerical results are shown to coincide with the
theoretical predictions of ideal, axisymmetric MHD to high accuracy.
Investigation of the influence of outer boundary conditions, particularly that
on the toroidal component of magnetic field shows that the commonly used
``free'' boundary condition leads to artificial magnetic forces which can act
to give spurious collimation. New boundary conditions are proposed which do not
generate artificial forces. Artificial results may also arise for cases where
the Mach cones on the outer boundaries are partially directed into the
simulation region.Comment: 19 pages, 18 figures, emulapj.sty is use
Nanostructural organization of naturally occurring composites - part II: silica-chitin-based biocomposites
Investigations of the micro- and nanostructures and chemical composition of the sponge skeletons as examples for natural structural biocomposites are of fundamental scientific relevance. Recently, we show that some demosponges (Verongula gigantea, Aplysina sp.) and glass sponges (Farrea occa, Euplectella aspergillum) possess chitin as a component of their skeletons. The main practical approach we used for chitin isolation was based on alkali treatment of corresponding external layers of spicules sponge material with the aim of obtaining alkali-resistant compounds for detailed analysis. Here, we present a detailed study of the structural and physicochemical properties of spicules of the glass sponge Rossella fibulata. The structural similarity of chitin derived from this sponge to invertebrate alpha chitin has been confirmed by us unambiguously using physicochemical and biochemical methods. This is the first report of a silica-chitin composite biomaterial found in Rossella species. Finally, the present work includes a discussion related to strategies for the practical application of silica-chitin-based composites as biomaterials
Searches for Physics Beyond the Standard Model at Colliders
All experimental measurements of particle physics today are beautifully
described by the Standard Model. However, there are good reasons to believe
that new physics may be just around the corner at the TeV energy scale. This
energy range is currently probed by the Tevatron and HERA accelerators and
selected results of searches for physics beyond the Standard Model are
presented here. No signals for new physics have been found and limits are
placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics,
Manchester, July 200
Panorama ambiental e fisio-molecular do arroz de terras altas.
Nessa revisão são descritos os diferentes ambientes na região produtora do arroz de terras altas no Brasil, os principais impactos que a planta de arroz de terras altas enfrenta em condições de deficiência hídrica e as perspectivas para mitigação dos efeitos desse tipo de estresse.bitstream/item/60714/1/seriedocumentos-274.pd
Self-Similar Magnetocentrifugal Disk Winds with Cylindrical Asymptotics
We construct a two-parameter family of models for self-collimated, radially
self-similar magnetized outflows from accretion disks. A flow at zero initial
poloidal speed leaves the surface of a rotating disk and is accelerated and
redirected toward the pole by helical magnetic fields threading the disk. At
large distances from the disk, the flow streamlines asymptote to wrap around
the surfaces of nested cylinders. In constrast to previous disk wind modeling,
we have explicitly implemented the cylindrical asymptotic boundary condition to
examine the consequences for flow dynamics. The solutions are characterized by
the logarithmic gradient of the magnetic field strength and the ratios between
the footpoint radius R_0 and asymptotic radius R_1 of streamlines; the Alfven
radius must be found as an eigenvalue. Cylindrical solutions require the
magnetic field to drop less steeply than 1/R. We find that the asymptotic
poloidal speed on any streamline is typically just a few tenths of the Kepler
speed at the corresponding disk footpoint. The asymptotic toroidal Alfven speed
is, however, a few times the footpoint Kepler speed. We discuss the
implications of the models for interpretations of observed optical jets and
molecular outflows from young stellar systems. We suggest that the difficulty
of achieving strong collimation in vector velocity simultaneously with a final
speed comparable to the disk rotation rate argues against isolated jets and in
favor of models with broader winds.Comment: 39 pages, Latex (uses AAS Latex macros), 6 eps figures, postscript
preprint with embedded figures available from
http://www.astro.umd.edu/~ostriker/professional/publications.html , to appear
in ApJ 9/1/9
Nonlinear growth of firehose and mirror fluctuations in turbulent galaxy-cluster plasmas
In turbulent high-beta astrophysical plasmas (exemplified by the galaxy
cluster plasmas), pressure-anisotropy-driven firehose and mirror fluctuations
grow nonlinearly to large amplitudes, dB/B ~ 1, on a timescale comparable to
the turnover time of the turbulent motions. The principle of their nonlinear
evolution is to generate secularly growing small-scale magnetic fluctuations
that on average cancel the temporal change in the large-scale magnetic field
responsible for the pressure anisotropies. The presence of small-scale magnetic
fluctuations may dramatically affect the transport properties and, thereby, the
large-scale dynamics of the high-beta astrophysical plasmas.Comment: revtex, 4 pages, 1 figure; replaced to match published versio
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