1,430 research outputs found
Copernicus observations of Betelgeuse and Antares
Copernicus observations of the M-supergiants, alpha Ori and alpha Sco, are presented. The MgII h and k resonance lines are strongly in emission in both stars. The k line is highly asymmetric in both stars but the h line is symmetric. Upper limits for several other resonance lines are given for alpha Ori. The possibility is explored that the k line asymmetry is caused by overlying resonance lines of MnI and FeI formed in the cool circumstellar gas shells around these stars. Observations of the MnI 4030-4033 A lines are used to show that circumstellar shell absorption is too weak to explain the asymmetry. It is suggested that the absorption occurs in a cool turbulent region between the base of the circumstellar shell and the top of the chromosphere
Switcher-random-walks: a cognitive-inspired mechanism for network exploration
Semantic memory is the subsystem of human memory that stores knowledge of
concepts or meanings, as opposed to life specific experiences. The organization
of concepts within semantic memory can be understood as a semantic network,
where the concepts (nodes) are associated (linked) to others depending on
perceptions, similarities, etc. Lexical access is the complementary part of
this system and allows the retrieval of such organized knowledge. While
conceptual information is stored under certain underlying organization (and
thus gives rise to a specific topology), it is crucial to have an accurate
access to any of the information units, e.g. the concepts, for efficiently
retrieving semantic information for real-time needings. An example of an
information retrieval process occurs in verbal fluency tasks, and it is known
to involve two different mechanisms: -clustering-, or generating words within a
subcategory, and, when a subcategory is exhausted, -switching- to a new
subcategory. We extended this approach to random-walking on a network
(clustering) in combination to jumping (switching) to any node with certain
probability and derived its analytical expression based on Markov chains.
Results show that this dual mechanism contributes to optimize the exploration
of different network models in terms of the mean first passage time.
Additionally, this cognitive inspired dual mechanism opens a new framework to
better understand and evaluate exploration, propagation and transport phenomena
in other complex systems where switching-like phenomena are feasible.Comment: 9 pages, 3 figures. Accepted in "International Journal of
Bifurcations and Chaos": Special issue on "Modelling and Computation on
Complex Networks
The irreducible unitary representations of the extended Poincare group in (1+1) dimensions
We prove that the extended Poincare group in (1+1) dimensions is
non-nilpotent solvable exponential, and therefore that it belongs to type I. We
determine its first and second cohomology groups in order to work out a
classification of the two-dimensional relativistic elementary systems.
Moreover, all irreducible unitary representations of the extended Poincare
group are constructed by the orbit method. The most physically interesting
class of irreducible representations corresponds to the anomaly-free
relativistic particle in (1+1) dimensions, which cannot be fully quantized.
However, we show that the corresponding coadjoint orbit of the extended
Poincare group determines a covariant maximal polynomial quantization by
unbounded operators, which is enough to ensure that the associated quantum
dynamical problem can be consistently solved, thus providing a physical
interpretation for this particular class of representations.Comment: 12 pages, Revtex 4, letter paper; Revised version of paper published
in J. Math. Phys. 45, 1156 (2004
Optical Particle Detection in Liquid Suspensions with a Hybrid Integrated Microsystem
AbstractA compact, robust and portable system for optical particle detection in liquid suspensions, achieved through the hybrid integration of commercial components, such as VCSELs and microlenses, in a silicon micromachined structure is presented. We demonstrate the feasibility of fabricating a device providing up to 4 collimated laser beams, with the ability of detecting and distinguishing microparticles of several diameters, even in mixed suspensions. This optical microsystem represents an alternative design for microflow cytometers based on optical fibres, and is aligned with the current tendency set by the Point-of-care devices
Discovery of a massive variable star with Z=Zo/36 in the galaxy DDO 68
The Local Volume dwarf galaxy DDO 68, from the spectroscopy of its two
brightest HII regions (Knots 1 and 2) was designated as the second most
metal-poor star-forming galaxy [12+log(O/H)=7.14]. In the repeated spectral
observations in 2008 January with the 6-m telescope (BTA) of the HII region
Knot 3 [having 12+log(O/H)=7.10+-0.06], we find a strong evidence of a
transient event related to a massive star evolution. From the follow-up
observation with the higher spectral resolution in 2008 February, we confirm
this phenomenon, and give parameters of its emission-line spectrum comprising
of Balmer HI and HeI lines. The luminosities of the strongest transient lines
(Ha, Hb) are of a few 10^36 erg s^-1. We also detected an additional continuum
component in the new spectrum of Knot 3, which displays the spectral energy
distribution raising to ultraviolet. The estimate of the flux of this continuum
leads us to its absolute V-band magnitude of ~-7.1. Based on the spectral
properties of this transient component, we suggest that it is related to an
evolved massive star of luminous blue variable type with Z=Zo/36. We briefly
discuss observational constraints on parameters of this unique (in the aspect
of the record low metallicity of the progenitor massive star) event and propose
several lines of its study.Comment: 6 pages, 5 Postscript figures, to appear in MNRAS Letters in June
2008 issu
Robustness of the European power grids under intentional attack
The power grid defines one of the most important technological networks of
our times and sustains our complex society. It has evolved for more than a
century into an extremely huge and seemingly robust and well understood system.
But it becomes extremely fragile as well, when unexpected, usually minimal,
failures turn into unknown dynamical behaviours leading, for example, to sudden
and massive blackouts. Here we explore the fragility of the European power grid
under the effect of selective node removal. A mean field analysis of fragility
against attacks is presented together with the observed patterns. Deviations
from the theoretical conditions for network percolation (and fragmentation)
under attacks are analysed and correlated with non topological reliability
measures.Comment: 7 pages, 4 figure
Influence of age, gender and obesity on pressure discomfort threshold of the foot: A cross-sectional study
[EN] Background: Foot pain is a highly prevalent health problem for which measures such as a pattern of Pressure Discomfort Threshold of the foot plantar surface can provide valuable information for orthosis design. This study aimed to describe such pattern as a tool for the assessment of painful conditions of the feet and to analyse how it modifies according to age, gender and obesity.
Methods: A cross-sectional study was performed with participants allocated in: Group 1 people aged 20 to 35 years, Group 2 aged 50 to 65 years and Group 3 aged over 65. Pressure Discomfort Threshold on twelve points of the foot plantar surface was measured with an adapted manual dynamometer. Inferential analyses of the data were performed using one-way analysis of variance (ANOVA) considering foot areas, age group, gender and obesity.
Findings: 36 participants were analysed. The pattern of Pressure Discomfort Threshold for all individuals showed a significantly higher threshold on the heel and external foot (P < 0.001, eta(2) = 0.124) and was statistical significantly influenced by age (P < 0.001, eta(2) = 0.17), especially in participants aged over 65; by gender, with women having higher values (P < 0.001, eta(2) = 0.13), and by obesity (P < 0.001, eta(2) = 0.19).
Interpretation: A Pressure Discomfort Threshold pattern exists in the foot plantar surface. The characteristics of the discomfort pattern of the foot and its association with aging, gender and obesity may have considerable implications for orthosis and footwear design.Dueñas, L.; Arnal-Gómez, A.; Aparicio, I.; Balasch-Bernat, M.; López-Bueno, L.; Gonzalez Garcia, JC.; Solves Camallonga, C.... (2021). Influence of age, gender and obesity on pressure discomfort threshold of the foot: A cross-sectional study. Clinical Biomechanics. 82(105252):1-7. https://doi.org/10.1016/j.clinbiomech.2020.105252S1782105252AKDEMIR, O., BILKAY, U., TIFTIKCIOGLU, Y. O., OZEK, C., YAN, H., ZHANG, F., & AKIN, Y. (2010). New alternative in treatment of callus. The Journal of Dermatology, 38(2), 146-150. doi:10.1111/j.1346-8138.2010.00978.xAnguera, J. A., & Gazzaley, A. (2012). Dissociation of motor and sensory inhibition processes in normal aging. Clinical Neurophysiology, 123(4), 730-740. doi:10.1016/j.clinph.2011.08.024Awale, A., Dufour, A. B., Katz, P., Menz, H. B., & Hannan, M. T. (2016). Link Between Foot Pain Severity and Prevalence of Depressive Symptoms. Arthritis Care & Research, 68(6), 871-876. doi:10.1002/acr.22779Bacarin, T. A., Sacco, I. C. N., & Hennig, E. M. (2009). Plantar pressure distribution patterns during gait in diabetic neuropathy patients with a history of foot ulcers. Clinics, 64(2). doi:10.1590/s1807-59322009000200008Barlow, A., Braid, S., & Jayson, M. (1990). Foot problems in the elderly. Clinical Rehabilitation, 4(3), 217-222. doi:10.1177/026921559000400306Betts, R. P., Franks, C. I., & Duckworth, T. (1980). Analysis of pressure and loads under the foot. II. Quantitation of the dynamic distribution. Clinical Physics and Physiological Measurement, 1(2), 113-124. doi:10.1088/0143-0815/1/2/002Bus, S. A., Ulbrecht, J. S., & Cavanagh, P. R. (2004). Pressure relief and load redistribution by custom-made insoles in diabetic patients with neuropathy and foot deformity. Clinical Biomechanics, 19(6), 629-638. doi:10.1016/j.clinbiomech.2004.02.010Caravaggi, P., Giangrande, A., Lullini, G., Padula, G., Berti, L., & Leardini, A. (2016). In shoe pressure measurements during different motor tasks while wearing safety shoes: The effect of custom made insoles vs. prefabricated and off-the-shelf. Gait & Posture, 50, 232-238. doi:10.1016/j.gaitpost.2016.09.013Duckworth, T., Boulton, A., Betts, R., Franks, C., & Ward, J. (1985). Plantar pressure measurements and the prevention of ulceration in the diabetic foot. The Journal of Bone and Joint Surgery. British volume, 67-B(1), 79-85. doi:10.1302/0301-620x.67b1.3968150Dufour, A. B., Broe, K. E., Nguyen, U.-S. D. T., Gagnon, D. R., Hillstrom, H. J., Walker, A. H., … Hannan, M. T. (2009). Foot pain: Is current or past shoewear a factor? Arthritis & Rheumatism, 61(10), 1352-1358. doi:10.1002/art.24733Von Elm, E., Altman, D. G., Egger, M., Pocock, S. J., Gøtzsche, P. C., & Vandenbroucke, J. P. (2008). The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Journal of Clinical Epidemiology, 61(4), 344-349. doi:10.1016/j.jclinepi.2007.11.008Fillingim, R. B. (2000). Sex, gender, and pain: Women and men really are different. Current Review of Pain, 4(1), 24-30. doi:10.1007/s11916-000-0006-6Gonzalez JC, García AC, Vivas MJ, Ferrús E, Alcántara E, Forner A. A new portable method for the measurement of pressure discomfort threshold on the foot plant. Fourth symposium of the Technical Group on Footwear Biomechanics. 5–7 August 1999. Canmore, Canada. International Society of Biomechanics.Gorter, K., Kuyvenhoven, M., & de Melker, R. (2000). Nontraumatic foot complaints in older people. A population-based survey of risk factors, mobility, and well-being. Journal of the American Podiatric Medical Association, 90(8), 397-402. doi:10.7547/87507315-90-8-397Greenspan, J. D., Craft, R. M., LeResche, L., Arendt-Nielsen, L., Berkley, K. J., Fillingim, R. B., … Traub, R. J. (2007). Studying sex and gender differences in pain and analgesia: A consensus report. Pain, 132(Supplement 1), S26-S45. doi:10.1016/j.pain.2007.10.014Hennig, E. M., & Sterzing, T. (2009). Sensitivity Mapping of the Human Foot: Thresholds at 30 Skin Locations. Foot & Ankle International, 30(10), 986-991. doi:10.3113/fai.2009.0986Hill, C. L., Gill, T. K., Menz, H. B., & Taylor, A. W. (2008). Prevalence and correlates of foot pain in a population-based study: the North West Adelaide health study. Journal of Foot and Ankle Research, 1(1). doi:10.1186/1757-1146-1-2Hills, A., Hennig, E., McDonald, M., & Bar-Or, O. (2001). Plantar pressure differences between obese and non-obese adults: a biomechanical analysis. International Journal of Obesity, 25(11), 1674-1679. doi:10.1038/sj.ijo.0801785Hong, W.-H., Lee, Y.-H., Chen, H.-C., Pei, Y.-C., & Wu, C.-Y. (2005). Influence of Heel Height and Shoe Insert on Comfort Perception and Biomechanical Performance of Young Female Adults During Walking. Foot & Ankle International, 26(12), 1042-1048. doi:10.1177/107110070502601208Le Johansson, L., Kjellberg, A., Kilbom, A., & Hagg, G. M. (1999). Perception of surface pressure applied to the hand. Ergonomics, 42(10), 1274-1282. doi:10.1080/001401399184947Kwan, R. L.-C., Zheng, Y.-P., & Cheing, G. L.-Y. (2010). The effect of aging on the biomechanical properties of plantar soft tissues. Clinical Biomechanics, 25(6), 601-605. doi:10.1016/j.clinbiomech.2010.04.003Machado, Á. S., Bombach, G. D., Duysens, J., & Carpes, F. P. (2016). Differences in foot sensitivity and plantar pressure between young adults and elderly. Archives of Gerontology and Geriatrics, 63, 67-71. doi:10.1016/j.archger.2015.11.005McPoil, T. G., & Cornwall, M. W. (2006). Plantar tactile sensory thresholds in healthy men and women. The Foot, 16(4), 192-197. doi:10.1016/j.foot.2006.07.001Messing, K., & Kilbom, Å. (2001). Standing and very slow walking: foot pain-pressure threshold, subjective pain experience and work activity. Applied Ergonomics, 32(1), 81-90. doi:10.1016/s0003-6870(00)00030-2Mickle, K. J., & Steele, J. R. (2015). Obese older adults suffer foot pain and foot-related functional limitation. Gait & Posture, 42(4), 442-447. doi:10.1016/j.gaitpost.2015.07.013Mickle, K. J., Munro, B. J., Lord, S. R., Menz, H. B., & Steele, J. R. (2010). Foot Pain, Plantar Pressures, and Falls in Older People: A Prospective Study. Journal of the American Geriatrics Society, 58(10), 1936-1940. doi:10.1111/j.1532-5415.2010.03061.xOkifuji, A., Bradshaw, D. H., & Olson, C. (2009). Evaluating obesity in fibromyalgia: neuroendocrine biomarkers, symptoms, and functions. Clinical Rheumatology, 28(4), 475-478. doi:10.1007/s10067-009-1094-2Redmond, A. C., Landorf, K. B., & Keenan, A.-M. (2009). Contoured, prefabricated foot orthoses demonstrate comparable mechanical properties to contoured, customised foot orthoses: a plantar pressure study. Journal of Foot and Ankle Research, 2(1). doi:10.1186/1757-1146-2-20Shrout, P. E., & Fleiss, J. L. (1979). Intraclass correlations: Uses in assessing rater reliability. Psychological Bulletin, 86(2), 420-428. doi:10.1037/0033-2909.86.2.420Veves, A., Murray, H. J., Young, M. J., & Boulton, A. J. M. (1992). The risk of foot ulceration in diabetic patients with high foot pressure: a prospective study. Diabetologia, 35(7), 660-663. doi:10.1007/bf00400259Weerasinghe, T. W., Goonetilleke, R. S., & Reischl, U. (2016). Pressure thresholds and stiffness on the plantar surface of the human foot. Ergonomics, 60(7), 985-996. doi:10.1080/00140139.2016.1229042Xiong, S., Goonetilleke, R. S., Witana, C. P., & Rodrigo, W. D. A. S. (2010). An indentation apparatus for evaluating discomfort and pain thresholds in conjunction with mechanical properties of foot tissue in vivo. The Journal of Rehabilitation Research and Development, 47(7), 629. doi:10.1682/jrrd.2009.09.0152Xiong, S., Goonetilleke, R. S., & Jiang, Z. (2011). Pressure thresholds of the human foot: measurement reliability and effects of stimulus characteristics. Ergonomics, 54(3), 282-293. doi:10.1080/00140139.2011.552736Xu, R., Wang, Z., Ma, T., Ren, Z., & Jin, H. (2019). Effect of 3D Printing Individualized Ankle-Foot Orthosis on Plantar Biomechanics and Pain in Patients with Plantar Fasciitis: A Randomized Controlled Trial. Medical Science Monitor, 25, 1392-1400. doi:10.12659/msm.915045Van der Zwaard, B. C., Elders, P. J., Knol, D. L., Gorter, K. J., Peeraer, L., van der Windt, D. A., & van der Horst, H. E. (2011). Treatment of forefoot problems in older people: study protocol for a randomised clinical trial comparing podiatric treatment to standardised shoe advice. Journal of Foot and Ankle Research, 4(1). doi:10.1186/1757-1146-4-1
Diversity, competition, extinction: the ecophysics of language change
As early indicated by Charles Darwin, languages behave and change very much
like living species. They display high diversity, differentiate in space and
time, emerge and disappear. A large body of literature has explored the role of
information exchanges and communicative constraints in groups of agents under
selective scenarios. These models have been very helpful in providing a
rationale on how complex forms of communication emerge under evolutionary
pressures. However, other patterns of large-scale organization can be described
using mathematical methods ignoring communicative traits. These approaches
consider shorter time scales and have been developed by exploiting both
theoretical ecology and statistical physics methods. The models are reviewed
here and include extinction, invasion, origination, spatial organization,
coexistence and diversity as key concepts and are very simple in their defining
rules. Such simplicity is used in order to catch the most fundamental laws of
organization and those universal ingredients responsible for qualitative
traits. The similarities between observed and predicted patterns indicate that
an ecological theory of language is emerging, supporting (on a quantitative
basis) its ecological nature, although key differences are also present. Here
we critically review some recent advances lying and outline their implications
and limitations as well as open problems for future research.Comment: 17 Pages. A review on current models from statistical Physics and
Theoretical Ecology applied to study language dynamic
Electronic transport in gadolinium atomic-size contacts
We report on the fabrication, transport measurements, and density functional theory (DFT) calculations of atomic-size contacts made of gadolinium (Gd). Gd is known to have local moments mainly associated with f electrons. These coexist with itinerant s and d bands that account for its metallic character. Here we explore whether and how the local moments influence electronic transport properties at the atomic scale. Using both scanning tunneling microscope and lithographic mechanically controllable break junction techniques under cryogenic conditions, we study the conductance of Gd when only few atoms form the junction between bulk electrodes made of the very same material. Thousands of measurements show that Gd has an average lowest conductance, attributed to single-atom contact, below 2e2h. Our DFT calculations for monostrand chains anticipate that the f bands are fully spin polarized and insulating and that the conduction may be dominated by s, p, and d bands. We also analyze the electronic transport for model nanocontacts using the nonequilibrium Green's function formalism in combination with DFT. We obtain an overall good agreement with the experimental results for zero bias and show that the contribution to the electronic transport from the f channels is negligible and that from the d channels is marginal.B.O., C.S., J.F.R., J.J.P., and C.U. acknowledge financial support by MEC-Spain (Grant No. FIS2013-47328-C2 and MAT2016-78625-C2) and the Generalitat Valenciana under Grant No. PROMETEO/2012/011. C.S. and J.J.P. acknowledge the EU structural funds and the Comunidad de Madrid under NANOFRONTMAG-CM program Grant No. S2013/MIT-2850. J.L.L. and J.F.R. acknowledge Marie Curie ITN SPINOGRAPH FP7 under REA Grant Agreement No. 607904-13. B.O. acknowledges financial support by MEC Spain (Grant No. FIS2010-21883-C02-01) under brief stays abroad scholarship
- …