A TDDFT study of the excited states of DNA bases and their assemblies

We present a detailed study of the optical absorption spectra of DNA bases and base pairs, carried out by means of time dependent density functional theory. The spectra for the isolated bases are compared to available theoretical and experimental data and used to assess the accuracy of the method and the quality of the exchange-correlation functional: Our approach turns out to be a reliable tool to describe the response of the nucleobases. Furthermore, we analyze in detail the impact of hydrogen bonding and $\pi$-stacking in the calculated spectra for both Watson-Crick base pairs and Watson-Crick stacked assemblies. We show that the reduction of the UV absorption intensity (hypochromicity) for light polarized along the base-pair plane depends strongly on the type of interaction. For light polarized perpendicular to the basal plane, the hypochromicity effect is reduced, but another characteristic is found, namely a blue shift of the optical spectrum of the base-assembly compared to that of the isolated bases. The use of optical tools as fingerprints for the characterization of the structure (and type of interaction) is extensively discussed.Comment: 31 pages, 8 figure

Excess of weight: is it a modifiable predictive and prognostic factor in locally advanced rectal cancer?

To evaluate the relationship between body mass index (BMI) and rates of treatment tolerance and clinical outcomes in patients with locally advanced rectal cancer treated with a multimodality approach. PATIENTS AND METHODS: This study was conducted on 56 patients with histologically proven rectal adenocarcinoma, staged T3-4, and/or node-positive tumor, which underwent intensified radiochemotherapy (RT-CHT) treatment before surgery. We calculated adiposity indices and analyzed their influence on treatment tolerance and clinical outcomes. RESULTS: Distribution of the 56 patients according to BMI was BMI < 25 kg/m2 (n = 19; 33.9%), BMI 25-29 kg/m2 (n = 29; 51.8%) and BMI ≥ 30 kg/m2 (n = 8; 14.3%). BMI had no significant influence on neo-adjuvant treatment-related toxicity. With a median follow-up of 23 months (range 11-47), the 2-year survival was 85.7%. We did not observe any significant difference among the three BMI categories for any of the outcomes. CONCLUSIONS: This study suggested no evident links between overweight and survival in patients with locally advanced rectal carcinoma treated with neo-adjuvant RT-CHT. Overweight patients tolerate treatment as normal-weight patients

Dark matter from dark energy-baryonic matter couplings

We present a scenario in which a scalar field dark energy is coupled to the trace of the energy momentum tensor of the baryonic matter fields. In the slow-roll regime, this interaction could give rise to the cosmological features of dark matter. We work out the cosmological background solutions and fit the parameters of the model using the Union 2 supernovae data set. Then, we develop the cosmological perturbations up to linear order, and we find that the perturbed variables have an acceptable behavior, in particular the density contrast of baryonic matter grows similar to that in the $\Lambda$CDM model for a suitable choice of the strength parameter of the coupling.Comment: 10 pages, 8 figures, in this version small typos are corrected and it matches the published version in Phys. Rev. D15, January 201

Perceptions of Doctoral Students Regarding Factors Contributing to Student Success

This third and final phase of a sequential exploratory mixed methoddesign sought to investigate doctoral student perspectives regardingsupport services that impede or assist in the completion of an Ed.D.program at a small, northeast university. Qualitative methods includedindividual interviews and qualitative reflections to probe studentperceptions regarding support program improvements, using their\u27stories\u27 to provide rich, descriptive details. Students emphasized theneed for better pre-enrollment preparation, a comprehensive orientationand advising program, and ongoing academic support services includingwriting assistance, research skills development, and networking andmentoring. Tinto\u27s (1987) integration theory provides the framework forthis study, using his six transformative dimensions for growth anddevelopment to interpret the findings

Weak-field limit of f(R)-gravity in three and more spatial dimensions

We investigate a point-like massive source in non-linear f(R) theories in the case of arbitrary number of spatial dimensions D\geq 3. If D>3 then extra dimensions undergo toroidal compactification. We consider a weak-field approximation with Minkowski and de Sitter background solutions. In both these cases point-like massive sources demonstrate good agreement with experimental data only in the case of ordinary three-dimensional (D=3) space. We generalize this result to the case of perfect fluid with dust-like equations of state in the external and internal spaces. This perfect fluid is uniformly smeared over all extra dimensions and enclosed in a three-dimensional sphere. In ordinary three dimensional (D=3) space, our formulas are useful for experimental constraints on parameters of f(R) models.Comment: 8 pages, Revtex4, no figure

Reheating via a generalized non-minimal coupling of curvature to matter

In this work one shows that a generalized non-minimal coupling between geometry and matter is compatible with Starobinsky inflation and leads to a successful process of preheating, a reheating scenario based on the production of massive particles via parametric resonance. The model naturally extends the usual preheating mechanism, which resorts to an {\it ad-hoc} scalar curvature-dependent mass term for a scalar field $\chi$, and also encompasses a previously studied preheating channel based upon a non-standard kinetic term.Comment: 12 page

The Formation of non-Keplerian Rings of Matter about Compact Stars

The formation of energetic rings of matter in a Kerr spacetime with an outward pointing acceleration field does not appear to have previously been noted as a relativistic effect. In this paper we show that such rings are a gravimagneto effect with no Newtonian analog, and that they do not occur in the static limit. The energy efficiency of these rings can, depending of the strength of the acceleration field, be much greater than that of Keplerian disks. The rings rotate in a direction opposite to that of compact star about which they form. The size and energy efficiency of the rings depend on the fundamental parameters of the spacetime as well as the strength the acceleration field.Comment: 19 pages, 7 figures, 1 diagram. Figures are included in the text using the "graphicx" package. If you do not have this package you can use epsfig, or another package as long as you alter the tex file appropriately. Alternatively you could print the figures out seperatel

Cosmological dynamics of fourth order gravity with a Gauss-Bonnet term

We consider cosmological dynamics in fourth order gravity with both $f(R)$ and $\Phi(\mathcal {G})$ correction to the Einstein gravity ($\mathcal{G}$ is the Gauss-Bonnet term). The particular case for which both terms are equally important on power-law solutions is described. These solutions and their stability are studied using the dynamical system approach. We also discuss condition of existence and stability of de Sitter solution in a more general situation of power-law $f$ and $\Phi$.Comment: published version, references update