Dissociation of Recovery of Muscle Activation and Force Following a Sustained Maximal Isometiric Contraction

To investigate time-dependency of nervous system recovery following muscular contractions, subjects (n=10) performed two bouts (B1, B2) of sustained maximal isometric handgrip contractions separated by 10- min recovery. Force and surface EMG were collected continuously throughout contraction bouts but were analyzed at 15 sec intervals (1 sec segments). iEMG and mean power frequency (MPF) were calculated for the brachioradialis (BR), flexor carpi radialis (FCR) flexor carpi ulnaris (FCU), and flexor digitorum profundus (FDP) muscles. Muscle activation (iEMG-MPF: BR:68-20%; FCR:72-16%; FCU: 65-20%; FDP:48-50%, respectively) and isometric force (88%) decreased following B1(120-sec contraction). Following recovery, initial force of B2 was significantly less than B1 (23%); however muscle activation (iEMG) was similar to B1 for BR, FCR and FDP. Initial B2 FCU iEMG activity was lower but increased to B1 levels by 15 sec; remaining similar throughout. MPF was similar and decreased similarly over time in both bouts but tended to be higher at initiation of B2. The mechanical response was similar in both bouts despite differences in initial force generation (B1: y = -0.172x+22.7; R2=0.98; B2: y = -0.182x+17.9 R2=0.97). Incomplete recovery of force observed in B2 suggests interference in excitation-contraction coupling while fatigue within each bout appears specifically related to changes in muscle activation

Flip Graphs of Degree-Bounded (Pseudo-)Triangulations

We study flip graphs of triangulations whose maximum vertex degree is bounded by a constant $k$. In particular, we consider triangulations of sets of $n$ points in convex position in the plane and prove that their flip graph is connected if and only if $k > 6$; the diameter of the flip graph is $O(n^2)$. We also show that, for general point sets, flip graphs of pointed pseudo-triangulations can be disconnected for $k \leq 9$, and flip graphs of triangulations can be disconnected for any $k$. Additionally, we consider a relaxed version of the original problem. We allow the violation of the degree bound $k$ by a small constant. Any two triangulations with maximum degree at most $k$ of a convex point set are connected in the flip graph by a path of length $O(n \log n)$, where every intermediate triangulation has maximum degree at most $k+4$.Comment: 13 pages, 12 figures, acknowledgments update

Acoustic Emission from crumpling paper

From magnetic systems to the crust of the earth, many physical systems that exibit a multiplicty of metastable states emit pulses with a broad power law distribution in energy. Digital audio recordings reveal that paper being crumpled, a system that can be easily held in hand, is such a system. Crumpling paper both using the traditional hand method and a novel cylindrical geometry uncovered a power law distribution of pulse energies spanning at least two decades: (exponent 1.3 - 1.6) Crumpling initally flat sheets into a compact ball (strong crumpling), we found little or no evidence that the energy distribution varied systematically over time or the size of the sheet. When we applied repetitive small deformations (weak crumpling) to sheets which had been previously folded along a regular grid, we found no systematic dependence on the grid spacing. Our results suggest that the pulse energy depends only weakly on the size of the paper regions responsible for sound production.Comment: 12 pages of text, 9 figures, submitted to Phys. Rev. E, additional information availible at http://www.msc.cornell.edu/~houle/crumpling

Fieldworker effects on substance use reporting in a Rural South African setting

Aims: Fieldworkers capturing reports of sensitive behaviors, such as substance use, may influence survey responses and represent an important factor in response validity. We explored the effects and interaction of fieldworker and respondent characteristics (age and gender) in substance (tobacco and alcohol) use reporting. We aim to further the literature on conditional social attribution effects on substance use reporting in the context of South Africa, where accurate estimates of modifiable risk factors are critical for medical and public health practitioners and policy-makers in efforts to reduce chronic disease burden and mortality.This project also received funding and administrative support from the University of Colorado Population Center, funded by the Eunice Shriver National Institute of Child Health and Human Development (NICHD R21 HD051146)

Semiclassical mechanics of a non-integrable spin cluster

We study detailed classical-quantum correspondence for a cluster system of three spins with single-axis anisotropic exchange coupling. With autoregressive spectral estimation, we find oscillating terms in the quantum density of states caused by classical periodic orbits: in the slowly varying part of the density of states we see signs of nontrivial topology changes happening to the energy surface as the energy is varied. Also, we can explain the hierarchy of quantum energy levels near the ferromagnetic and antiferromagnetic states with EKB quantization to explain large structures and tunneling to explain small structures.Comment: 9 pages. For related works see "http://www.msc.cornell.edu/~clh/clh.html

Caracterización fisicoquímica del agua de la laguna La Vega Escondida, Tampico, Tamaulipas-México - Physicochemical water characterization of La Vega Escondida Lake, Tampico, Tamaulipas-México

La laguna La Vega Escondida se ubica al Noroeste del municipio de Tampico, Tamaulipas. Es un área natural protegida, que colinda con la zona conurbada de Tampico, Madero y Altamira, que además del beneficio ecológico,es una fuente de abastecimiento de agua potable para la ciudad de Tampico. Por lo cual es importante conocer la composición fisicoquímica del agua de esta laguna, con el fin de proteger tanto el ecosistema como la salud humana. Este estudio, evaluó la concentración de los parámetros fisicoquímicos del agua (pH, conductividad eléctrica, sólidos totales, temperatura, cloruros, dureza, alcalinidad, sulfatos, demanda química de oxígeno y oxígeno disuelto), así como la distribución espacial de éstos dentro de la laguna. Los resultados obtenidos, se compararon con los criterios ecológicos de la calidad del agua (CE-CCA-001-SEMARNAT, 1989) y con la Norma Oficial Mexicana (NOM-127-SSA1-1994), obteniéndose que en los parámetros analizados el agua cumple con la calidad requerida para mantener la vida acuática y captación para consumo humano, excepto en el parámetro de sólidos suspendidos totales (SST). Se observó además que los patrones de distribución espacial de los parámetros fisicoquímicos son heterogéneos y que hay diferencias significativas en el parámetro OD (profundidades), así como en el pH y la CE (puntos de muestreo), al nivel de significancia del 5 %

Stripes and holes in a two-dimensional model of spinless fermions and hardcore bosons

We consider a Hubbard-like model of strongly-interacting spinless fermions and hardcore bosons on a square lattice, such that nearest neighbor occupation is forbidden. Stripes (lines of holes across the lattice forming antiphase walls between ordered domains) are a favorable way to dope this system below half-filling. The problem of a single stripe can be mapped to a spin-1/2 chain, which allows understanding of its elementary excitations and calculation of the stripe's effective mass for transverse vibrations. Using Lanczos exact diagonalization, we investigate the excitation gap and dispersion of a hole on a stripe, and the interaction of two holes. We also study the interaction of two, three, and four stripes, finding that they repel, and the interaction energy decays with stripe separation as if they are hardcore particles moving in one (transverse) direction. To determine the stability of an array of stripes against phase separation into particle-rich phase and hole-rich liquid, we evaluate the liquid's equation of state, finding the stripe-array is not stable for bosons but is possibly stable for fermions.Comment: 24 pages, 18 figure

Good Genes and Sexual Selection in Dung Beetles (Onthophagus taurus): Genetic Variance in Egg-to-Adult and Adult Viability

Whether species exhibit significant heritable variation in fitness is central for sexual selection. According to good genes models there must be genetic variation in males leading to variation in offspring fitness if females are to obtain genetic benefits from exercising mate preferences, or by mating multiply. However, sexual selection based on genetic benefits is controversial, and there is limited unambiguous support for the notion that choosy or polyandrous females can increase the chances of producing offspring with high viability. Here we examine the levels of additive genetic variance in two fitness components in the dung beetle Onthophagus taurus. We found significant sire effects on egg-to-adult viability and on son, but not daughter, survival to sexual maturity, as well as moderate coefficients of additive variance in these traits. Moreover, we do not find evidence for sexual antagonism influencing genetic variation for fitness. Our results are consistent with good genes sexual selection, and suggest that both pre- and postcopulatory mate choice, and male competition could provide indirect benefits to females

Natural genetic variation in fluctuating asymmetry of wing shape in Drosophila melanogaster

Fluctuating asymmetry (FA), defined as random deviation from perfect symmetry, has been used to assay the inability of individuals to buffer their developmental processes from environmental perturbations (i.e., developmental instability). In this study, we aimed to characterize the natural genetic variation in FA of wing shape in Drosophila melanogaster, collected from across the Japanese archipelago. We quantified wing shapes at whole wing and partial wing component levels and evaluated their mean and FA. We also estimated the heritability of the mean and FA of these traits. We found significant natural genetic variation in all the mean wing traits and in FA of one of the partial wing components. Heritability estimates for mean wing shapes were significant in two and four out of five wing traits in males and females, respectively. On the contrary, heritability estimates for FA were low and not significant. This is a novel study of natural genetic variation in FA of wing shape. Our findings suggest that partial wing components behave as distinct units of selection for FA, and local adaptation of the mechanisms to stabilize developmental processes occur in nature