Disorder-induced double resonant Raman process in graphene

An analytical study is presented of the double resonant Raman scattering process in graphene, responsible for the D and D$^{\prime}$ features in the Raman spectra. This work yields analytical expressions for the D and D$^{\prime}$ integrated Raman intensities that explicitly show the dependencies on laser energy, defect concentration, and electronic lifetime. Good agreement is obtained between the analytical results and experimental measurements on samples with increasing defect concentrations and at various laser excitation energies. The use of Raman spectroscopy to identify the nature of defects is discussed. Comparison between the models for the edge-induced and the disorder-induced D band intensity suggests that edges or grain boundaries can be distinguished from disorder by the different dependence of their Raman intensity on laser excitation energy. Similarly, the type of disorder can potentially be identified not only by the intensity ratio $I_{\mathrm{D}}/I_{\mathrm{D}^{\prime}}$, but also by its laser energy dependence. Also discussed is a quantitative analysis of quantum interference effects of the graphene wavefunctions, which determine the most important phonon wavevectors and scattering processes responsible for the D and D$^{\prime}$ bands.Comment: 10 pages, 4 figure

Cost optimization of singly and doubly reinforced concrete beams with EC2-2001

A model for the optimal design of rectangular reinforced concrete sections is presented considering the stress–strain diagrams described in EC2-2001 and MC90. The following expressions are developed: economic bending moment; optimal area of steel and optimal steel ratio between upper and lower steel. All the expressions are in nondimensional form. The present model is applied to four different classes of concrete described in MC90. It is concluded that in nondimensional form the equations are nearly coincident for both singly and doubly reinforcement. It is also concluded that the ultimate strain for concrete in the compression zone, ecm, lies between the strain for peak stress ec1 and the ultimate strain ecu. This result is relevant once that the maximum moment is obtained for this value, and not the value ecu, as defined in EC2-2001. Cost optimization is implemented in the code and compared with other optimum models based on the ultimate design of ACI

Desenvolvimento inicial e trocas gasosas do meloeiro sob temperatura elevada.

O objetivo desse trabalho foi avaliar o crescimento inicial e as trocas gasosas de meloeiros crescidos sob dois diferentes regimes de temperatura

Exact Energy-Time Uncertainty Relation for Arrival Time by Absorption

We prove an uncertainty relation for energy and arrival time, where the arrival of a particle at a detector is modeled by an absorbing term added to the Hamiltonian. In this well-known scheme the probability for the particle's arrival at the counter is identified with the loss of normalization for an initial wave packet. Under the sole assumption that the absorbing term vanishes on the initial wave function, we show that $\Delta T \Delta E \geq \sqrt p \hbar/2$ and $\Delta E\geq 1.37\sqrt p\hbar$, where $e$ denotes the mean arrival time, and $p$ is the probability for the particle to be eventually absorbed. Nearly minimal uncertainty can be achieved in a two-level system, and we propose a trapped ion experiment to realize this situation.Comment: 8 pages, 2 figure

O mercado algodoeiro no Brasil: crises e perspectivas.

bitstream/CNPA-2009-09/14620/1/CIRTEC44.pd

Aspectos econômicos e sociais da cotonicultura no Nordeste do Brasil.

bitstream/CNPA/14459/1/CIRTEC31.PD