90 research outputs found
Expression Levels of Thymidylate Synthase, Thymidylate Phosphorylase and Dihydropyrimidine Dehydrogenase in Head and Neck Squamous Cell Carcinoma: Preliminary Study
Introduction Pharyngo-laryngeal tumors classified as T3-4, N0-3, M0, are conventionally treated by mutilating surgery (total (pharyngo)-laryngectomy). Neo-adjuvant chemotherapy with 5-FU/platinum salt can be proposed in an attempt to preserve the larynx. The level of the response to chemotherapy ranges from 36 to 54% of cases. Thus, a large number of patients receive chemotherapy that is ineffective and not free from adverse effects. Three main enzymes are involved in the metabolism of 5-FU: thymidylate synthase (TS), thymidylate phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD). Several studies suggest that a high level of expression of these three genes correlates with a poor clinical response to 5-FU. The main purpose of our study was to look for a correlation between the levels of expression of the genes for sensitivity to 5-FU (TS, TP, DPD) within the tumor and the clinical response observed after three courses of chemotherapy combining 5-FU/platinum salt in patients presenting with advanced cancer of the pharyngolarynx. Methods This was a prospective genetic study that had required approval from the Ethics Committee. The main assessment criterion was based on the assessment of the clinical response by an ENT panendoscopy and a cervical CT scan, after three courses of chemotherapy. The expression of the genes was determined by quantitative RT-PCR, using total RNA extracted from tumor biopsies taken during the initial panendoscopy. Results The means calculated, in our study, for the three genes of interest (TS, TP, DPD) were lower in the responder group than those in the non-responder group. Discussion Our preliminary findings reveal trends that confirm the hypothesis that the lower the level of expression of the sensitivity genes, the better the clinical response to chemotherapy. They now form part of a larger study that is currently in progress
Charge and spin order in one-dimensional electron systems with long-range Coulomb interactions
We study a system of electrons interacting through long--range Coulomb forces
on a one--dimensional lattice, by means of a variational ansatz which is the
strong--coupling counterpart of the Gutzwiller wave function. Our aim is to
describe the quantum analogue of Hubbard's classical ``generalized Wigner
crystal''. We first analyse charge ordering in a system of spinless fermions,
with particular attention to the effects of lattice commensurability. We argue
that for a general (rational) number of electrons per site there are three
regimes, depending on the relative strength of the long--range Coulomb
interaction (as compared to the hopping amplitude ). For very large the
quantum ground state differs little from Hubbard's classical solution, for
intermediate to large values of we recover essentially the Wigner crystal
of the continuum model, and for small the charge modulation amounts to a
small--amplitude charge--density wave. We then include the spin degrees of
freedom and show that in the Wigner crystal regimes (i.e. for large ) they
are coupled by an antiferromagnetic kinetic exchange , which turns out to be
smaller than the energy scale governing the charge degrees of freedom. Our
results shed new light on the insulating phases of organic quasi--1D compounds
where the long--range part of the interaction is unscreened, and magnetic and
charge orderings coexist at low temperatures.Comment: 11 pages, 7 figures, accepted for publication on Phys. Rev.
Domain Walls in Two-Component Dynamical Lattices
We introduce domain-wall (DW) states in the bimodal discrete nonlinear
Schr{\"{o}}dinger equation, in which the modes are coupled by cross phase
modulation (XPM). By means of continuation from various initial patterns taken
in the anti-continuum (AC) limit, we find a number of different solutions of
the DW type, for which different stability scenarios are identified. In the
case of strong XPM coupling, DW configurations contain a single mode at each
end of the chain. The most fundamental solution of this type is found to be
always stable. Another solution, which is generated by a different AC pattern,
demonstrates behavior which is unusual for nonlinear dynamical lattices: it is
unstable for small values of the coupling constant (which measures the
ratio of the nonlinearity and coupling lengths), and becomes stable at larger
. Stable bound states of DWs are also found. DW configurations generated by
more sophisticated AC patterns are identified as well, but they are either
completely unstable, or are stable only at small values of . In the case of
weak XPM, a natural DW solution is the one which contains a combination of both
polarizations, with the phase difference between them 0 and at the
opposite ends of the lattice. This solution is unstable at all values of ,
but the instability is very weak for large , indicating stabilization as the
continuum limit is approached. The stability of DWs is also verified by direct
simulations, and the evolution of unstable DWs is simulated too; in particular,
it is found that, in the weak-XPM system, the instability may give rise to a
moving DW.Comment: 14 pages, 14 figures, Phys. Rev. E (in press
Can forest management based on natural disturbances maintain ecological resilience?
Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance
Relaxation channels of two-vibron bound states in \alpha-helix proteins
Relaxation channels for two-vibron bound states in an anharmonic alpha-helix
protein are studied. It is pointed out that the relaxation originates in the
interaction between the dressed anharmonic vibrons and the remaining phonons.
This interaction is responsible for the occurrence of transitions between
two-vibron eigenstates mediated by both phonon absorption and phonon emission.
At biological temperature, it is shown that the relaxation rate does not
significantly depends on the nature of the two-vibron state involved in the
process. Therefore, the lifetime for both bound and free states is of the same
order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameters.
By contrast, the relaxation channels strongly depend on the nature of the
two-vibron states which is a consequence of the breather-like behavior of the
two-vibron bound states.Comment: octobre 2003 - soumis Phys. Rev.
ReflexÔes sobre o ensino de dinùmica de grupo para alunos de graduação em enfermagem
Le sous-solage en plantation de palmier a huile. Presentation d'un outil adapte et des conditions de realisation.
National audienc
Controlled dissolution of quartz material.Part II. Quartz chemical etching applied to blanks industrial manufacturing
In many electronic applications, chemical etching process is used to manufacture the substrates. This method has been applied for long on quartz crystal blanks manufacturing for minor adjustments of the vibration frequencies. This paper presents a way to implement an industrial chemical etching process specially dedicated for large thickness removals without damaging the blanks surface texture. It will be shown how were defined the choice of the etching solvent, and the most sensitive parameters. An industrial equipment will be presented whose principle was deduced from the sensitivity study of these parameters. Finally, the electrical performances of the resonators processed on this equipment will be compared with the performances achieved by conventional means
- âŠ