Comparación de tests: Cooper y Rockport

La presente investigación compara los tests de Cooper y Rockport según las variables frecuencia cardiaca (FC), consumo máximo de oxígeno (VO2máx.), valoración del esfuerzo percibido y distancia ¿ tiempo. La muestra se corresponde con 27 alumnos de 2º de ESO de un instituto de Madrid. El registro de FC se hizo a través de pulsómetros en periodos de 60 segundos. Se constataron para el test de Cooper, FC máx > 200 lat.· min-1 en el 66,6 % (sexo femenino). El 100 % (sexo masculino) registró FC > 200 lat.· min-1. En el test de Rockport los valores de FC fueron inferiores; el 40 % (sexo femenino) registró FC > 200 lat.· min-1 y el 44,4% (sexo masculino) observó una FC > 200 lat.· min-1. Cinco sujetos superaron su FC máxima teórica. Se constata diferencias significativas en la valoración de la escala del esfuerzo percibido entre los tests (sexo femenino) y en la valoración del VO2máx. en ambos sexos

Revival of Silenced Echo and Quantum Memory for Light

We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed gain and spontaneous emission generate prohibitive noise. A second $\pi$-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.Comment: 13 pages, 6 figure

Leaf litter breakdown budgets in streams of various trophic status: effects of dissolved inorganic nutrients on microorganisms and invertebrates

1. We investigated the effect of trophic status on the organic matter budget in freshwater ecosystems. During leaf litter breakdown, the relative contribution of the functional groups and the quantity/quality of organic matter available to higher trophic levels are expected to be modified by the anthropogenic release of nutrients. 2. Carbon budgets were established during the breakdown of alder leaves enclosed in coarse mesh bags and submerged in six streams: two oligotrophic, one mesotrophic, two eutrophic and one hypertrophic streams. Nitrate concentrations were 4.5–6.7 mg L−1 and the trophic status of each stream was defined by the soluble reactive phosphorus concentration ranging from 3.4 (oligotrophic) to 89 μg L−1 (hypertrophic). An ammonium gradient paralleled the phosphate gradient with mean concentrations ranging from 1.4 to 560 μg L−1 NH4-N. The corresponding unionised ammonia concentrations ranged from 0.08 to 19 μg L−1 NH3-N over the six streams. 3. The dominant shredder taxa were different in the oligo-, meso- and eutrophic streams. No shredders were observed in the hypertrophic stream. These changes may be accounted for by the gradual increase in the concentration of ammonia over the six streams. The shredder biomass dramatically decreased in eu- and hypertrophic streams compared with oligo- and mesotrophic. 4. Fungal biomass increased threefold from the most oligotrophic to the less eutrophic stream and decreased in the most eutrophic and the hypertrophic. Bacterial biomass increased twofold from the most oligotrophic to the hypertrophic stream. Along the trophic gradient, the microbial CO2 production followed that of microbial biomass whereas the microbial fine particulate organic matter and net dissolved organic carbon (DOC) did not consistently vary. These results indicate that the microorganisms utilised the substrate and the DOC differently in streams of various trophic statuses. 5. In streams receiving various anthropogenic inputs, the relative contribution of the functional groups to leaf mass loss varied extensively as a result of stimulation and the deleterious effects of dissolved inorganic compounds. The quality/quantity of the organic matter produced by microorganisms slightly varied, as they use DOC from stream water instead of the substrate they decompose in streams of higher trophic status

Large self-deflection of soliton beams in LiNbO3

We report the observation of large self-deflection of 2-D bright photorefractive solitons in LiNbO(3) crystal under a dc applied field. Beam deflection as large as 300 mu m after a 7 mm. propagation distance is reported, leading to formation of curved 2-D waveguides. We attribute this large deflection to the low level of impurity acceptors present in the samples, as confirmed by numerical results from a time-dependent photorefractive model

Physical activity and smoking habit in adolescent students

El objetivo de este estudio fue detectar en qué medida afecta la actividad física y el hábito tabáquico en estudiantes de Enseñanza Secundaria. Se estudiaron 168 adolescentes no fumadores y fumadores recién iniciados. Se midieron peso, talla, presión arterial, frecuencia cardíaca, actividad física, fuerza, flexibilidad y resistencia y una prueba espirométrica. Tanto en chicas y chicos fumadores, se evidenciaron peores resultados en la mayoría de los parámetros espirométricos (FEV1, FEF25-75%, FVC) y un envejecimiento prematuro del pulmón, más acentuado en chicas. La actividad físico-deportiva moderada se asocia a adolescentes que menos fuman y tienen más facilidad para abandonar el hábito tabáquicoThe aim of the study was to detect how physical education and smoking habits affect secondary school students, 168 non smokers and newly initiated were studied. Weight, height, heart rate, blood pressure, physical activity, strength, flexibility and endurance, and spirometric tests were analyzed. In both, female and male smokers, obtained worse results in the mayority of spirometric parameters (FEV1, FEF25-75%, FVC) and premature lung ageing, more pointed in females. Moderate physical-sporting activity is associated to adolescents who smoke less and quit smoking more easil

Homogeneous Conformal String Backgrounds

We present exact solutions characterised by Bianchi-type I,II,III,V,VI four-dimensional metric, space-independent dilaton, and vanishing torsion background, for the low energy string effective action with zero central charge deficit. We show that, in such a context, curvature singularities cannot be avoided, except for the trivial case of flat spacetime and constant dilaton. We also provide a further example of the failure of the standard prescription for connecting conformal string backgrounds through duality transformations associated to non-semisimple, non-Abelian isometry group.Comment: 20 pages, latex, no figures, to appear in Class. Q. Gra

Isotropization of Bianchi-Type Cosmological Solutions in Brans-Dicke Theory

The cosmic, general analitic solutions of the Brans--Dicke Theory for the flat space of homogeneous and isotropic models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions --which includes cosmological models with the open and the closed spaces of the Friedmann--Robertson--Walker metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi--Type metric clasification-- when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scalar field, $\phi$, times a function of the mean scale factor or ``volume element'', $a^3 = a_1 a_2 a_3$, which depends on time and on the barotropic index of the equation of state used, can be written as a function of a ``cosmic time'' reduced in terms of another function of the mean scale factor depending itself again on the barotropic index but independent of the metrics here employed. This reduction procedure permites one to analyze if explicitly given anisotropic cosmological solutions ``isotropize'' in the course of their time evolution. For if so can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations.Comment: 15 pages, Late

Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory

Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curve ($k\neq0$) Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special issue dedicated in honour of Prof. H. Dehne

Localization, Coulomb interactions and electrical heating in single-wall carbon nanotubes/polymer composites

Low field and high field transport properties of carbon nanotubes/polymer composites are investigated for different tube fractions. Above the percolation threshold f_c=0.33%, transport is due to hopping of localized charge carriers with a localization length xi=10-30 nm. Coulomb interactions associated with a soft gap Delta_CG=2.5 meV are present at low temperature close to f_c. We argue that it originates from the Coulomb charging energy effect which is partly screened by adjacent bundles. The high field conductivity is described within an electrical heating scheme. All the results suggest that using composites close to the percolation threshold may be a way to access intrinsic properties of the nanotubes by experiments at a macroscopic scale.Comment: 4 pages, 5 figures, Submitted to Phys. Rev.