1,466 research outputs found
Interleukin-2 and histamine in combination inhibit tumour growth and angiogenesis in malignant glioma
Biotherapy including interleukin-2 (IL-2) treatment seems to be more effective outside the central nervous system when compared to the effects obtained when the same tumour is located intracerebrally. Recently published studies suggest that reduced activity of NK cells in tumour tissue can be increased by histamine. The present study was designed to determine whether IL-2 and histamine, alone or in combination, can induce anti-tumour effects in an orthotopic rat glioma model. One group of rats was treated with histamine alone (4 mg kg–1s.c. as daily injections from day 6 after intracranial tumour implantation), another group with IL-2 alone as a continuous subcutaneous infusion and a third group with both histamine and IL-2. The animals were sacrificed at day 24 after tumour implantation. IL-2 and histamine in combination significantly reduced tumour growth. The microvessel density was significantly reduced, an effect mainly affecting the small vessels. No obvious alteration in the pattern of VEGF mRNA expression was evident and no significant changes in apoptosis were observed. Neither IL-2 nor histamine alone caused any detectable effects on tumour growth. Histamine caused an early and pronounced decline in tumour blood flow compared to normal brain. The results indicate that the novel combination of IL-2 and histamine can be of value in reducing intracerebral tumour growth and, thus, it might be of interest to re-evaluate the therapeutic potential of biotherapy in malignant glioma. © 2000 Cancer Research Campaig
Prolonged injury symptoms and later visits to psychiatric care after mild traumatic brain injury in school-age
Objective To investigate demographic and pre-injury factors in Finnish school-aged children admitted to pediatric neurology services after mild traumatic brain injury (mTBI). The relation of these factors to prolonged injury symptoms and later visits into psychiatric care was assessed. Methods Demographic information, pre-injury learning status, and neuropsychological test results of 120 patients aged 7-16 years were retrospectively collected from the hospital medical records. Data were compared with self- or parent-reported injury symptoms at 1-3 months post-injury and later visits to psychiatric care. Results According to medical records, 14.2% of the children with mTBI had a diagnosed neurobehavioral or psychiatric condition pre-injury. Additionally, 53.3% of the children had some neurobehavioral or psychiatric concerns or traits prior to the injury. Over half (56.7%) of the children studied were symptomatic at 1-3 months following the injury. Female gender and presence of prolonged symptoms were predictive for later visit into psychiatric care. Conclusions Pre-injury neurobehavioral or psychiatric problems may predict prolonged injury symptoms following pediatric mTBI. In this retrospective patient series, prolonged symptoms and female gender seem to predict the need for later psychiatric care. Monitoring the recovery of children with mTBI and pre-injury risk factors is important for timely interventions.Peer reviewe
Twisting Graphene Nanoribbons into Carbon Nanotubes
Although carbon nanotubes consist of honeycomb carbon, they have never been
fabricated from graphene directly. Here, it is shown by quantum
molecular-dynamics simulations and classical continuum-elasticity modeling,
that graphene nanoribbons can, indeed, be transformed into carbon nanotubes by
means of twisting. The chiralities of the tubes thus fabricated can be not only
predicted but also externally controlled. This twisting route is an opportunity
for nanofabrication, and is easily generalizable to ribbons made of other
planar nanomaterials.Comment: 9 pages, 10 figure
Current-spin-density functional study of persistent currents in quantum rings
We present a numerical study of persistent currents in quantum rings using
current spin density functional theory (CSDFT). This formalism allows for a
systematic study of the joint effects of both spin, interactions and impurities
for realistic systems. It is illustrated that CSDFT is suitable for describing
the physical effects related to Aharonov-Bohm phases by comparing energy
spectra of impurity-free rings to existing exact diagonalization and
experimental results. Further, we examine the effects of a symmetry-breaking
impurity potential on the density and current characteristics of the system and
propose that narrowing the confining potential at fixed impurity potential will
suppress the persistent current in a characteristic way.Comment: 7 pages REVTeX, including 8 postscript figure
Direct Coulomb and Exchange Interaction in Artificial Atoms
We determine the contributions from the direct Coulomb and exchange
interactions to the total interaction in semiconductor artificial atoms. We
tune the relative strengths of the two interactions and measure them as a
function of the number of confined electrons. We find that electrons tend to
have parallel spins when they occupy nearly degenerate single-particle states.
We use a magnetic field to adjust the single-particle state degeneracy, and
find that the spin-configurations in an arbitrary magnetic field are well
explained in terms of two-electron singlet and triplet states.Comment: 4 pages, 5 figure
Older people's views on professional competences
info:eu-repo/semantics/publishedVersio
Cones, pringles, and grain boundary landscapes in graphene topology
A polycrystalline graphene consists of perfect domains tilted at angle
{\alpha} to each other and separated by the grain boundaries (GB). These nearly
one-dimensional regions consist in turn of elementary topological defects,
5-pentagons and 7-heptagons, often paired up into 5-7 dislocations. Energy
G({\alpha}) of GB computed for all range 0<={\alpha}<=Pi/3, shows a slightly
asymmetric behavior, reaching ~5 eV/nm in the middle, where the 5's and 7's
qualitatively reorganize in transition from nearly armchair to zigzag
interfaces. Analysis shows that 2-dimensional nature permits the off-plane
relaxation, unavailable in 3-dimensional materials, qualitatively reducing the
energy of defects on one hand while forming stable 3D-landsapes on the other.
Interestingly, while the GB display small off-plane elevation, the random
distributions of 5's and 7's create roughness which scales inversely with
defect concentration, h ~ n^(-1/2)Comment: 9 pages, 4 figure
Interactions in Chaotic Nanoparticles: Fluctuations in Coulomb Blockade Peak Spacings
We use random matrix models to investigate the ground state energy of
electrons confined to a nanoparticle. Our expression for the energy includes
the charging effect, the single-particle energies, and the residual screened
interactions treated in Hartree-Fock. This model is applicable to chaotic
quantum dots or nanoparticles--in these systems the single-particle statistics
follows random matrix theory at energy scales less than the Thouless energy. We
find the distribution of Coulomb blockade peak spacings first for a large dot
in which the residual interactions can be taken constant: the spacing
fluctuations are of order the mean level separation Delta. Corrections to this
limit are studied using the small parameter 1/(kf L): both the residual
interactions and the effect of the changing confinement on the single-particle
levels produce fluctuations of order Delta/sqrt(kf L). The distributions we
find are significantly more like the experimental results than the simple
constant interaction model.Comment: 17 pages, 4 figures, submitted to Phys. Rev.
Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes
The small mass and atomic-scale thickness of graphene membranes make them
highly suitable for nanoelectromechanical devices such as e.g. mass sensors,
high frequency resonators or memory elements. Although only atomically thick,
many of the mechanical properties of graphene membranes can be described by
classical continuum mechanics. An important parameter for predicting the
performance and linearity of graphene nanoelectromechanical devices as well as
for describing ripple formation and other properties such as electron
scattering mechanisms, is the bending rigidity, {\kappa}. In spite of the
importance of this parameter it has so far only been estimated indirectly for
monolayer graphene from the phonon spectrum of graphite, estimated from AFM
measurements or predicted from ab initio calculations or bond-order potential
models. Here, we employ a new approach to the experimental determination of
{\kappa} by exploiting the snap-through instability in pre-buckled graphene
membranes. We demonstrate the reproducible fabrication of convex buckled
graphene membranes by controlling the thermal stress during the fabrication
procedure and show the abrupt switching from convex to concave geometry that
occurs when electrostatic pressure is applied via an underlying gate electrode.
The bending rigidity of bilayer graphene membranes under ambient conditions was
determined to be eV. Monolayers have significantly lower
{\kappa} than bilayers
Correlation energy and spin polarization in the 2D electron gas
The ground state energy of the two--dimensional uniform electron gas has been
calculated with fixed--node diffusion Monte Carlo, including backflow
correlations, for a wide range of electron densities as a function of spin
polarization. We give a simple analytic representation of the correlation
energy which fits the density and polarization dependence of the simulation
data and includes several known high- and low-density limits. This
parametrization provides a reliable local spin density energy functional for
two-dimensional systems and an estimate for the spin susceptibility. Within the
proposed model for the correlation energy, a weakly first--order polarization
transition occurs shortly before Wigner crystallization as the density is
lowered.Comment: Minor typos corrected, see erratum: Phys. Rev. Lett. 91, 109902(E)
(2003
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