5,494 research outputs found
Distribuição espacial das necessidades hÃdricas das culturas do feijão, milho e soja na bacia do rio Tibaji, PR.
bitstream/item/89786/1/BOP-16.pd
Hemispheric asymmetry in visuospatial attention assessed with transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) was used to study visuospatial attention processing in ten healthy volunteers. In a forced choice recognition task the subjects were confronted with two symbols simultaneously presented during 120ms at random positions, one in the left and the other in the right visual field. The subject had to identify the presented pattern out of four possible combinations and to press the corresponding response key within 2 s. Double-pulse TMS (dTMS) with a 100-ms interstimulus interval (ISI) and an intensity of 80% of the stimulator output (corresponding to 110-120% of the motor threshold) was applied by a nonfocal coil over the right or left posterior parietal cortex (PPC, corresponding to P3/P4 of the international 10-20 system) at different time intervals after onset of the visual stimulus (starting at 120ms, 270ms and 520ms). Double-pulse TMS over the right PPC starting at 270ms led to a significant increase in percentage of errors in the contralateral, left visual field (median: 23% with TMS vs 13% without TMS, P=0.0025). TMS applied earlier or later showed no effect. Furthermore, no significant increase in contra- or ipsilateral percentage of errors was found when the left parietal cortex was stimulated with the same timing. These data indicate that: (1) parietal influence on visuospatial attention is mainly controlled by the right lobe since the same stimulation over the left parietal cortex had no significant effect, and (2) there is a vulnerable time window to disturb this cortical process, since dTMS had a significant effect on the percentage of errors in the contralateral visual hemifield only when applied 270ms after visual stimulus presentatio
Generation of Magnetic Field by Combined Action of Turbulence and Shear
The feasibility of a mean-field dynamo in nonhelical turbulence with
superimposed linear shear is studied numerically in elongated shearing boxes.
Exponential growth of magnetic field at scales much larger than the outer scale
of the turbulence is found. The charateristic scale of the field is l_B ~
S^{-1/2} and growth rate is gamma ~ S, where S is the shearing rate. This newly
discovered shear dynamo effect potentially represents a very generic mechanism
for generating large-scale magnetic fields in a broad class of astrophysical
systems with spatially coherent mean flows.Comment: 4 pages, 5 figures; replaced with revised version that matches the
published PR
Are serial CA 19-9 kinetics helpful in predicting survival in patients with advanced or metastatic pancreatic cancer treated with gemcitabine and cisplatin?
Background: Serial kinetics of serum CA 19-9 levels have been reported to reflect response and survival in patients with pancreatic cancer undergoing surgery, radiotherapy, and chemotherapy. We prospectively studied serial kinetics of serum CA 19-9 levels of patients with locally advanced or metastatic disease treated with gemcitabine and cisplatin. Patients and Methods: Enrolled in the study were 87 patients (female/male = 26/61; stage III/IV disease = 24/63). Patients received gemcitabine 1,000 mg/m(2) on days 1, 8, and 15 plus cisplatin 50 mg/m(2) on days 1 and 15, every 4 weeks. Serum samples were collected at the onset of chemotherapy and before the start of a new treatment cycle (day 28). Results: 77 of 87 patients (88.5%) with initially elevated CA 19-9 levels were included for evaluation. According to imaging criteria, 4 (5.2%) achieved a complete remission and 11 (14.3%) achieved partial remission, yielding an overall response rate of 19.5%. 43 (55.8%) patients were CA 19-9 responders, defined by greater than or equal to50% decrease in CA 19-9 serum levels within 2 months after treatment initiation. Except for one, all patients who had responded by imaging criteria (n = 14) fulfilled the criterion of a CA 19-9 responder. Despite being characterized as non-responders by CT-imaging criteria (stable/progressive disease), 29 patients were classified as CA 19-9 responders (positive predictive value 32.5%). Independent of the response evaluation by CT, CA 19-9 responders survived significantly longer than CA 19-9 non-responders (295 d; 95% CI: 285-445 vs. 174 d; 95% CI: 134-198; p = 0.022). Conclusion: CA 19-9 kinetics in serum serve as an early and reliable indicator of response and help to predict survival in patients with advanced pancreatic cancer receiving effective treatment with gemcitabine and cisplatin
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
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
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
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
- …