Influence of symmetry and Coulomb-correlation effects on the optical properties of nitride quantum dots

The electronic and optical properties of self-assembled InN/GaN quantum dots (QDs) are investigated by means of a tight-binding model combined with configuration interaction calculations. Tight-binding single particle wave functions are used as a basis for computing Coulomb and dipole matrix elements. Within this framework, we analyze multi-exciton emission spectra for two different sizes of a lens-shaped InN/GaN QD with wurtzite crystal structure. The impact of the symmetry of the involved electron and hole one-particle states on the optical spectra is discussed in detail. Furthermore we show how the characteristic features of the spectra can be interpreted using a simplified Hamiltonian which provides analytical results for the interacting multi-exciton complexes. We predict a vanishing exciton and biexciton ground state emission for small lens-shaped InN/GaN QDs. For larger systems we report a bright ground state emission but with drastically reduced oscillator strengths caused by the quantum confined Stark effect.Comment: 15 pages, 17 figure

A supercritical series analysis for the generalized contact process with diffusion

We study a model that generalizes the CP with diffusion. An additional transition is included in the model so that at a particular point of its phase diagram a crossover from the directed percolation to the compact directed percolation class will happen. We are particularly interested in the effect of diffusion on the properties of the crossover between the universality classes. To address this point, we develop a supercritical series expansion for the ultimate survival probability and analyse this series using d-log Pad\'e and partial differential approximants. We also obtain approximate solutions in the one- and two-site dynamical mean-field approximations. We find evidences that, at variance to what happens in mean-field approximations, the crossover exponent remains close to $\phi=2$ even for quite high diffusion rates, and therefore the critical line in the neighborhood of the multicritical point apparently does not reproduce the mean-field result (which leads to $\phi=0$) as the diffusion rate grows without bound

Refining a questionnaire to assess breast cancer knowledge and barriers to screening in Kenya: Psychometric assessment of the BCAM

Background Our study objective was to determine the validity and reliability of the breast module of a cancer awareness measure (BCAM) among adult women in western Kenya. Methods The study was conducted between October and November 2012, following three breast cancer screening events. Purposive and systematic random sampling methods were used to identity 48 women for cognitive focus group discussions, and 1061 (594 who attended vs. 467 who did not attend screening events) for surveys, respectively. Face and psychometric validity of the BCAM survey was assessed using cognitive testing, factor analysis of survey data, and correlations. Internal reliability was assessed using Cronbach’s alpha. Results Among survey participants, the overall median age was 34 (IQR: 26–44) years. Compared to those women who did not attend the screening events, women attendees were older (median: 35 vs. 32 years, p = 0.001) more often married (79% vs. 72%, p = 0.006), more educated (52% vs. 46% with more than an elementary level of education, p = 0.001), more unemployed (59% vs. 11%, p = 0.001), more likely to report doing breast self-examination (56% vs. 40%, p = 0.001) and more likely to report having felt a breast lump (16% vs. 7%, p = 0.001). For domain 1 on knowledge of breast cancer symptoms, one factor (three items) with Eigen value of 1.76 emerged for the group that did not attend screening, and 1.50 for the group that attended screening. For both groups two factors (factor 1 “internal influences” and factor 2 “external influences”) emerged among domain 4 on barriers to screening, with varied item loadings and Eigen values. There were no statistically significant differences in the factor scores between attendees and non-attendees. There were significant associations between factor scores and other attributes of the surveyed population, including associations with occupation, transportation type, and training for and practice of breast self-examination. Cronbach’s alpha showed an acceptable internal consistency. Conclusion Certain subpopulations are less likely than others to attend breast screening in Kenya. A survey measure of breast cancer knowledge and perceived barriers to screening shows promise for use in Kenya for characterizing clinical and community population beliefs, but needs adaptation for setting, language and culture

Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides

We propose that the pseudogap state observed in the transition metal oxides can be explained by a three-dimensional flux state, which exhibits spontaneously generated currents in its ground state due to electron-electron correlations. We compare the energy of the flux state to other classes of mean field states, and find that it is stabilized over a wide range of $t$ and $\delta$. The signature of the state will be peaks in the neutron diffraction spectra, the location and intensity of which are presented. The dependence of the pseudogap in the optical conductivity is calculated based on the parameters in the model.Comment: submitted to Phys. Rev. B on January 8, 200

Fractional recurrence in discrete-time quantum walk

Quantum recurrence theorem holds for quantum systems with discrete energy eigenvalues and fails to hold in general for systems with continuous energy. We show that during quantum walk process dominated by interference of amplitude corresponding to different paths fail to satisfy the complete quantum recurrence theorem. Due to the revival of the fractional wave packet, a fractional recurrence characterized using quantum P\'olya number can be seen.Comment: 10 pages, 11 figure : Accepted to appear in Central European Journal of Physic

Apoptosis and p53 status predict the efficacy of postoperative administration of UFT in non-small cell lung cancer

To examine whether efficacy of postoperative oral administration of UFT, a 5-fluorouracil derivative chemotherapeutic agent, may be influenced by incidence of apoptosis (apoptosis index) or apoptosis-related gene status (p53 and bcl-2) of the tumour, a total of 162 patients with pathologic stage I non-small cell lung cancer were retrospectively reviewed. UFT was administrated postoperatively to 44 patients (UFT group), and not to the other 118 patients (Control group). For all patients, 5-year survival rate of the UFT group (79.9%) seemed higher than that of the Control group (69.8%), although without significant difference (P = 0.054). For patients with higher apoptotic index, 5-year survival rate of the UFT group (83.3%) was significantly higher than that of the Control group (67.6%, P = 0.039); for patients with lower apoptotic index, however, there was no difference in the prognosis between these two groups. Similarly, UFT was effective for patients without p53 aberrant expression (5-year survival rates: 95.2% for the UFT group and 74.3% for the Control group, P = 0.022), whereas not effective for patients with p53 aberrant expression. Bcl-2 status did not influence the efficacy of UFT. In conclusion, apoptotic index and p53 status are useful factors to predict the efficacy of postoperative adjuvant therapy using UFT. © 2001 Cancer Research Campaign http://www.bjcancer.co

Valence bond solids for SU(n) spin chains: exact models, spinon confinement, and the Haldane gap

To begin with, we introduce several exact models for SU(3) spin chains: (1) a translationally invariant parent Hamiltonian involving four-site interactions for the trimer chain, with a three-fold degenerate ground state. We provide numerical evidence that the elementary excitations of this model transform under representation 3bar of SU(3) if the original spins of the model transform under rep. 3. (2) a family of parent Hamiltonians for valence bond solids of SU(3) chains with spin reps. 6, 10, and 8 on each lattice site. We argue that of these three models, only the latter two exhibit spinon confinement and hence a Haldane gap in the excitation spectrum. We generalize some of our models to SU(n). Finally, we use the emerging rules for the construction of VBS states to argue that models of antiferromagnetic chains of SU(n) spins in general possess a Haldane gap if the spins transform under a representation corresponding to a Young tableau consisting of a number of boxes \lambda which is divisible by n. If \lambda and n have no common divisor, the spin chain will support deconfined spinons and not exhibit a Haldane gap. If \lambda and n have a common divisor different from n, it will depend on the specifics of the model including the range of the interaction.Comment: 26 pages two-column style, 15 figures, revtex4; references adde

Study of the one-dimensional off-lattice hot-monomer reaction model

Hot monomers are particles having a transient mobility (a ballistic flight) prior to being definitely absorbed on a surface. After arriving at a surface, the excess energy coming from the kinetic energy in the gas phase is dissipated through degrees of freedom parallel to the surface plane. In this paper we study the hot monomer-monomer adsorption-reaction process on a continuum (off-lattice) one-dimensional space by means of Monte Carlo simulations. The system exhibits second-order irreversible phase transition between a reactive and saturated (absorbing) phases which belong to the directed percolation (DP) universality class. This result is interpreted by means of a coarse-grained Langevin description which allows as to extend the DP conjecture to transitions occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.

Impact of an Educational Intervention on Breast Cancer Knowledge in Western Kenya

Our objective was to assess the effectiveness of educational sessions that accompanied breast cancer screening events in three communities in western Kenya between October and November 2013. Five hundred and thirty-two women were recruited to complete a test of breast cancer-relevant knowledge and randomly allocated to ‘pre-test’ or ‘post-test’ groups that immediately preceded or followed participation in the educational sessions. The education was organized as a presentation by health professionals and focused mainly on causes of breast cancer, early and late cancer presentation signs, high-risk groups, screening methods to find early-stage breast cancer, self-breast exam procedures and treatment options for this disease. Participants were invited to ask questions and practice finding nodules in silicone breast models. The median age was 35 years (interquartile range: 28–45), and 86% had not undergone breast cancer screening previously. Many individual items in our test of knowledge showed statistically significant shifts to better-informed responses. When all items in the assessment questionnaire were scored as a ‘test’, on average there was a 2.80 point (95% CI: 2.38, 3.22) significant improvement in knowledge about breast cancer after the educational session. Our study provides evidence for the effectiveness of an educational strategy carefully tailored for women in these communities in Kenya

Hybrid Monte Carlo algorithm for the Double Exchange Model

The Hybrid Monte Carlo algorithm is adapted to the simulation of a system of classical degrees of freedom coupled to non self-interacting lattices fermions. The diagonalization of the Hamiltonian matrix is avoided by introducing a path-integral formulation of the problem, in $d+1$ Euclidean space-time. A perfect action formulation allows to work on the continuum euclidean time, without need for a Trotter-Suzuki extrapolation. To demonstrate the feasibility of the method we study the Double Exchange Model in three dimensions. The complexity of the algorithm grows only as the system volume, allowing to simulate in lattices as large as $16^3$ on a personal computer. We conclude that the second order paramagnetic-ferromagnetic phase transition of Double Exchange Materials close to half-filling belongs to the Universality Class of the three-dimensional classical Heisenberg model.Comment: 20 pages plus 4 postscript figure