On a special class of primitive words

When representing DNA molecules as words, it is necessary to take into account the fact that a word u encodes basically the same information as its Watson-Crick complement θ(u), where θ denotes the Watson-Crick complementarity function. Thus, an expression which involves only a word u and its complement can be still considered as a repeating sequence. In this context, we define and investigate the properties of a special class of primitive words, called pseudo-primitive words relative to θ or simply θ-primitive words, which cannot be expressed as such repeating sequences. For instance, we prove the existence of a unique θ-primitive root of a given word, and we give some constraints forcing two distinct words to share their θ-primitive root. Also, we present an extension of the well-known Fine and Wilf theorem, for which we give an optimal bound.     

On pseudoknot-bordered words and their properties

We study a generalization of the classical notions of bordered and unbordered words, motivated by biomolecular computing. DNA strands can be viewed as finite strings over the alphabet {A, G, C, T}, and are used in biomolecular computing to encode information. Due to the fact that A is Watson–Crick complementary to T and G to C, DNA single strands that are Watson–Crick complementary can bind to each other or to themselves forming so-called secondary structures. Most of these secondary structures are undesirable for biomolecular computational purposes since the strands they involve cannot further interact with other strands. This paper studies pseudoknot-bordered words, a mathematical formalization of pseudoknot-like inter- and intra-molecular structures. In this context, pseudoknot-unbordered words model DNA or RNA strands that will be free of such secondary structures. We obtain several properties of pseudoknot-bordered and -unbordered words. We also address following problem: Given a pseudoknot-unbordered word u, does ${\{u\}}^{+}$ consist of pseudoknot-unbordered words only? We show that this is not generally true. We find that a sufficient condition for ${\{u\}}^{+}$ to consist of pseudoknot-unbordered words only is that u be not primitive. All of our results hold for arbitrary antimorphic involutions, of which the DNA Watson–Crick complementarity function is a particular case.     

An integrated cross-layer framework of adaptive FEedback REsource allocation and Prediction for OFDMA systems

Orthogonal frequency division multiple access (OFDMA) technology has been adopted by 4th generation (a.k.a. 4G) telecommunication systems to achieve high system spectral efficiency. A crucial research issue is how to design adaptive feedback mechanisms so that the base station can use adaptive modulation and coding (AMC) techniques to adjust its data rate based on the channel condition. This problem is even more challenging in resource-limited and heterogeneous multiuser environments such as Mobile WiMAX and long-term evolution (LTE) networks. In this paper, we develop an integrated cross-layer framework of adaptive FEedback REsource allocation and Prediction (FEREP) for OFDMA systems. The proposed framework, implemented at the base station side, is composed of three modules. The feedback window adaptation (FWA) module dynamically tunes the feedback window size for each user based on the received automatic repeat request (ARQ) messages that reflect the current channel condition. The priority-based feedback scheduling (PBFS) module then performs feedback resource allocation by taking into account the feedback window size, the user profile and the total system feedback budget. To choose adapted modulation and coding schemes (MCS), the channel quality indicator prediction (CQIP) module performs channel prediction by using recursive least square (RLS) algorithm for the users whose channel feedback has not been granted for schedule in current frame. Through extensive simulations, the proposed framework shows significant performance gain especially under stringent feedback budget constraints.     

Carbon-steel corrosion in multiphase slug flow and CO2

Hydrocarbon multiphase flow may exhibit various geometric configurations or flow patterns. One of these flow patterns is known as multiphase slug flow. If CO₂ is present in hydrocarbons, the steel pipelines can be corroded as this process is probably enhanced by slug flow turbulence. A hydrodynamic circuit was built to study the CO₂ corrosion rates under different slug flow conditions. The experimental results show how the corrosion rate of a carbon-steel electrode varies according to the flow turbulence. The higher slug frequency used in this study was 80 slugs/min. Experimental results for pressure drop and slug length are in agreement with the Dukler and Hubbard [A model for gas-liquid slug flow in horizontal and near horizontal tubes, Ind. Eng. Chem. Fundam. 14 (1975) 337-347] multiphase flow model. Furthermore, the experimental slug frequencies are well correlated by the Shell and Gregory [Correlation of the liquid volume fraction in the slug for horizontal gas-liquid slug flow. Int. J. Multiphase Flow 4 (1978) 33-39] equations in horizontal pipes.     

Frequency-resolved absorption tomography with tunable diode lasers

A tunable diode laser was used for absorption tomography in an axisymmetric atmospheric pressure flat-flame burner. A rapid tomographic inversion algorithm was used to facilitate the many reconstructions at a relatively sparse set of projections typical of laser absorption tomography. Profiles of temperature and CO2 mole fraction were measured simultaneously in methane-air flames. Absorption measurements were made near the R-branch bandhead at 4.17 microm to minimize interferences with other species, while providing good temperature and concentration sensitivity at flame conditions. The procedure showed the advantage of reconstructing detailed spectra at each radial node.     

Adult age differences in sensitivity to semantic structure of prose.

50 18–33 yr olds and 43 62–67 yr olds from low- and high-education populations heard narrative passages at different presentation rates and difficulty levels in 2 experiments. Immediately after listening to a tape-recorded version of each story, Ss orally recalled it. Results consistently demonstrate that younger Ss remembered more than older ones, but Ss from all groups favored the main ideas in their recalls. Also, Ss from all ages and educational levels were equally able to identify the important information in the stories. It is suggested that sensitivity to the semantic structure of prose is not a major component of adult age differences in discourse comprehension. It is further suggested that adult age differences observed on discourse comprehension tasks may reflect an age-related decline in processing capacity. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new model for the prediction of oxygen interference in hydrogen storage systems

A new model is developed to analyze oxygen interference in hydrogen storage materials. It is based on the competitive adsorption isotherm between the two gases, with the parameters fitted from molecular dynamic simulations. The model is applied to a system consisting of graphene sheets separated by different distances. For a gas-phase mixture of hydrogen (99.9%) and oxygen (0.1%) in interaction with porous graphite of 6.5 Å (optimum size) it can be observed that after 50 cycles of charging/discharging the blocking of active sites of the material by oxygen is ∼10%, due to progressive pollution of the system by oxygen. The model presented here may easily be extended to other systems of interest, involving other blocking species or adsorbent materials.