534 research outputs found
The effect of a nucleating agent on lamellar growth in melt-crystallizing polyethylene oxide
The effects of a (non co-crystallizing) nucleating agent on secondary
nucleation rate and final lamellar thickness in isothermally melt-crystallizing
polyethylene oxide are considered. SAXS reveals that lamellae formed in
nucleated samples are thinner than in the pure samples crystallized at the same
undercoolings. These results are in quantitative agreement with growth rate
data obtained by calorimetry, and are interpreted as the effect of a local
decrease of the basal surface tension, determined mainly by the nucleant
molecules diffused out of the regions being about to crystallize. Quantitative
agreement with a simple lattice model allows for some interpretation of the
mechanism.Comment: submitted to Journal of Applied Physics (first version on 22 Apr
2002
Idiopathic Myenteric Ganglionitis Underlying Acute âDramaticâ Intestinal Pseudoobstruction: Report of an Exceptional Case
Inflammation of the myenteric plexus of the gastrointestinal tract is a very rare pathological condition, with few reports in the medical literature. This pathological condition causes atonic gut motor dysfunction and is principally secondary to other diseases, being reported nearly solely as a paraneoplastic phenomenon in neuroendocrine lung tumors, including small cell carcinomas or neuroblastomas. In addition it can also be associated with disorders of the central nervous system, although it has rarely been described in Chagas disease. It has been named âidiopathic myenteric ganglionitisâ because no apparent causes can be demonstrated. We report the clinicopathologic findings of an exceptional case of a young woman affected by severe chronic constipation suddenly changing into acute intestinal pseudoobstruction with dramatic evolution. Relationships between ganglionitis, idiopathic constipation and acute intestinal pseudoobstruction as well as therapeutic implications are discussed
Neutron Tomography at INES: First experimental results
A neutron tomography apparatus has been designed and installed at the Italian neutron experimental station (INES) at ISIS (UK). The instrument has a double aim: an additional opportunity for the INES users and a âbench testâ for an instrument component that will be proposed for installation on some of the new neutron scattering instruments of Target Station 2 (TS2) of ISIS. Here, we present the first experimental results achieved with this apparatus
Fusion rate enhancement due to energy spread of colliding nuclei
Experimental results for sub-barrier nuclear fusion reactions show cross
section enhancements with respect to bare nuclei which are generally larger
than those expected according to electron screening calculations. We point out
that energy spread of target or projectile nuclei is a mechanism which
generally provides fusion enhancement. We present a general formula for
calculating the enhancement factor and we provide quantitative estimate for
effects due to thermal motion, vibrations inside atomic, molecular or crystal
system, and due to finite beam energy width. All these effects are marginal at
the energies which are presently measurable, however they have to be considered
in future experiments at still lower energies. This study allows to exclude
several effects as possible explanation of the observed anomalous fusion
enhancements, which remain a mistery.Comment: 17 pages with 3 ps figure included. Revtex styl
Measurement of the 18Ne(a,p_0)21Na reaction cross section in the burning energy region for X-ray bursts
The 18Ne(a,p)21Na reaction provides one of the main HCNO-breakout routes into
the rp-process in X-ray bursts. The 18Ne(a,p_0)21Na reaction cross section has
been determined for the first time in the Gamow energy region for peak
temperatures T=2GK by measuring its time-reversal reaction 21Na(p,a)18Ne in
inverse kinematics. The astrophysical rate for ground-state to ground-state
transitions was found to be a factor of 2 lower than Hauser-Feshbach
theoretical predictions. Our reduced rate will affect the physical conditions
under which breakout from the HCNO cycles occurs via the 18Ne(a,p)21Na
reaction.Comment: 5 pages, 3 figures, accepted for publication on Physical Review
Letter
Theory of the Trojan-Horse Method
The Trojan-Horse method is an indirect approach to determine the energy
dependence of S-factors of astrophysically relevant two-body reactions. This is
accomplished by studying closely related three-body reactions under quasi-free
scattering conditions. The basic theory of the Trojan-Horse method is developed
starting from a post-form distorted wave Born approximation of the T-matrix
element. In the surface approximation the cross section of the three-body
reaction can be related to the S-matrix elements of the two-body reaction. The
essential feature of the Trojan-Horse method is the effective suppression of
the Coulomb barrier at low energies for the astrophysical reaction leading to
finite cross sections at the threshold of the two-body reaction. In a modified
plane wave approximation the relation between the two-body and three-body cross
sections becomes very transparent. The appearing Trojan-Horse integrals are
studied in detail.Comment: 27 pages, REVTeX4, 4 figures, 1 tabl
Influence of tumor microenvironment and fibroblast population plasticity on melanoma growth, therapy resistance and immunoescape
Cutaneous melanoma (CM) tissue represents a network constituted by cancer cells and tumor microenvironment (TME). A key feature of CM is the high structural and cellular plasticity of TME, allowing its evolution with disease and adaptation to cancer cell and environmental alter-ations. In particular, during melanoma development and progression each component of TME by interacting with each other and with cancer cells is subjected to dramatic structural and cellular modifications. These alterations affect extracellular matrix (ECM) remodelling, phenotypic profile of stromal cells, cancer growth and therapeutic response. The stromal fibroblast populations of the TME include normal fibroblasts and melanomaâassociated fibroblasts (MAFs) that are highly abun-dant and flexible cell types interacting with melanoma and stromal cells and differently influencing CM outcomes. The shift from the normal microenvironment to TME and from normal fibroblasts to MAFs deeply sustains CM growth. Hence, in this article we review the features of the normal mi-croenvironment and TME and describe the phenotypic plasticity of normal dermal fibroblasts and MAFs, highlighting their roles in normal skin homeostasis and TME regulation. Moreover, we dis-cuss the influence of MAFs and their secretory profiles on TME remodelling, melanoma progres-sion, targeted therapy resistance and immunosurveillance, highlighting the cellular interactions, the signalling pathways and molecules involved in these processes
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
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