Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud. II. The extended sample

All galaxies that have been adequately examined so far have shown an extended stellar halo. To search for such a halo in the LMC we have obtained low-resolution spectra for 100 LMC RR Lyrae stars, of which 87 are in the field and 13 in the clusters NGC1835 and NGC2019. We measured radial velocities for 87 LMC RR Lyrae stars, and metallicities for 78 RR Lyrae stars, nearly tripling the previous sample. These targets are located in 10 fields covering a wide range of distances, out to 2.5 degrees from the center of the LMC. Our main result is that the mean velocity dispersion for the LMC RR Lyrae stars is 50+-2km/s. This quantity does not appear to vary with distance from the LMC center. The metallicity shows a Gaussian distribution, with mean [Fe/H]=-1.53+-0.02dex, and dispersion 0.20 dex in the Harris metallicity scale, confirming that they represent a very homogeneous metal-poor population. There is no dependence between the kinematics and metallicity of the field RR Lyrae star population. Using good quality low-resolution spectra from FORS1, FORS2 and GEMINI-GMOS we have found that field RR Lyrae stars in the LMC show a large velocity dispersion and that this indicate the presence of old and metal-poor stellar halo. All the evidence so far for the halo, however, is from the spectroscopy of the inner LMC regions, similar to the inner flattened halo in our Galaxy. Further study is necessary to confirm this important result.Comment: 12 pages, 4 figure

Biomechanical demands differentiate transitioning vs. continuous stair ascent gait in older women

Background Stair ascent mechanics change with age, but little is known about the differing functional demands of transitioning and continuous ascent. Work investigating the risky transition from gait to ascent is sparse, and the strategies that older adults adopt to achieve these demanding tasks have not been investigated. Methods This study compared the biomechanics of a 2-step transitional (floor-to-step2) and continuous ascent cycle (step1-to-step3) and investigated the role of limb preference in relation to dynamometer-derived knee strength during this transition. A biomechanical analysis of 36 women (60–83 years) ascending a 3-step staircase was conducted. Findings The 2-step transitioning cycle was completed quicker, with a larger range of motion, increased forces, larger knee flexor and dorsiflexor moments and ankle powers (P ≤ 0.05), but reduced hip and knee flexion, smaller hip extensor moments and hip and knee powers compared to continuous ascent. During the transition, 44% of the participants demonstrated a consistent limb preference. In these cases large between-limb extensor strength differences existed (13.8%) and 71% of these participants utilised the stronger limb to execute the 2-step transitional cycle. Interpretation The preferential stronger-limb 2-step transitioning strategy conflicts with previous recommendations of a stronger lead limb for frail/asymmetric populations. Our findings suggest that most healthy older women with large between-limb differences utilise the stronger limb to achieve the considerable propulsion required to redirect momentum during the 2-step transition. The biomechanical demands of ascent, relative to limb strength, can inform exercise programmes by targeting specific muscle groups to help older adults maintain/improve general functioning

Biomechanical demands of the 2-step transitional gait cycles linking level gait and stair descent gait in older women

Stair descent is an inherently complex form of locomotion posing a high falls risk for older adults, specifically when negotiating the transitional gait cycles linking level gait and descent. The aim of this study was to enhance our understanding of the biomechanical demands by comparing the demands of these transitions. Lower limb kinematics and kinetics of the 2-step transitions linking level and descent gait at the top (level-to-descent) and the bottom (descent-to-level) of the staircase were quantified in 36 older women with no falls history. Despite undergoing the same vertical displacement (2-steps), the following significant (p<.05) differences were observed during the top transition compared to the bottom transition: reduced step velocity; reduced hip extension and increased ankle dorsiflexion (late stance/pre-swing); reduced ground reaction forces, larger knee extensor moments and powers (absorption; late stance); reduced ankle plantarflexor moments (early and late stance) and increased ankle powers (mid-stance). Top transition biomechanics were similar to those reported previously for continuous descent. Kinetic differences at the knee and ankle signify the contrasting and prominent functions of controlled lowering during the top transition and forward continuance during the bottom transition. The varying musculoskeletal demands encountered during each functional sub-task should be addressed in falls prevention programmes with elderly populations where the greatest clinical impact may be achieved. Knee extensor eccentric power through flexion exercises would facilitate a smooth transition at the top and improving ankle plantarflexion strength during single and double limb stance activities would ease the transition into level gait following continuous descent

Symmetry structure and phase transitions

We study chiral symmetry structure at finite density and temperature in the presence of external magnetic field and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.Comment: Plenary talk given at the 4th. ICPAQGP held at Jaipur, India from Nov 26-30, 2001.laTex 2e file with 8 ps figures and 12 page

First microlensing candidate towards M31 from the Nainital Microlensing Survey

We report our first microlensing candidate NMS-E1 towards M31 from the data accumulated during the four years of Nainital Microlensing Survey. Cousin R and I band observations of ~13'x13' field in the direction of M31 have been carried out since 1998 and data is analysed using the pixel technique proposed by the AGAPE collaboration. NMS-E1 lies in the disk of M31 at \alpha = 0:43:33.3 and \delta = +41:06:44, about 15.5 arcmin to the South-East direction of the center of M31. The degenerate Paczy\'{n}ski fit gives a half intensity duration of ~59 days. The photometric analysis of the candidate shows that it reached R~20.1 mag at the time of maximum brightness and the colour of the source star was estimated to be (R-I)_0 ~ 1.1 mag. The microlensing candidate is blended by red variable stars; consequently the light curves do not strictly follow the characteristic Paczy\'{n}ski shape and achromatic nature. However its long period monitoring and similar behaviour in R and I bands supports its microlensing nature.Comment: no changes except typos corrected, to appear in A&

Search for an annual modulation of dark-matter signals with a germanium spectrometer at the Sierra Grande Laboratory

Data collected during three years with a germanium spectrometer at the Sierra Grande underground laboratory have been analyzed for distinctive features of annual modulation of the signal induced by WIMP dark matter candidates. The main motivation for this analysis was the recent suggestion by the DAMA/NaI Collaboration that a yearly modulation signal could not be rejected at the 90% confidence level when analyzing data obtained with a high-mass low-background scintillator detector. We performed two different analyses of the data: First, the statistical distribution of modulation-significance variables (expected from an experiment running under the conditions of Sierra Grande) was compared with the same variables obtained from the data. Second, the data were analyzed in energy bins as an independent check of the first result and to allow for the possibility of a crossover in the expected signal. In both cases no statistically significant deviation from the null result was found, which could support the hypothesis that the data contain a modulated component. A plot is also presented to enable the comparison of these results to those of the DAMA collaboration.Comment: New version accepted by Astroparticle Physics. Changes suggested by the referee about the theoretical prediction of rates are included. Conclusions remain unaffected. 14 pages, LaTeX, 7 figures. Uses epsfig macr

Dynamical evolution of the Universe in the quark-hadron phase transition and possible nugget formation

We study the dynamics of first-order phase transition in the early Universe when it was $10-50 \mu s$ old with quarks and gluons condensing into hadrons. We look at how the Universe evolved through the phase transition in small as well as large super cooling scenario, specifically exploring the formation of quark nuggets and their possible survival. The nucleation of the hadron phase introduces new distance scales in the Universe, which we estimate along with the hadron fraction, temperature, nucleation time etc. It is of interest to explore whether there is a relic signature of this transition in the form of quark nuggets which might be identified with the recently observed dark objects in our galactic halo and account for the Dark Matter in the Universe at present.Comment: LaTeX file with four postscript figure

Can a galaxy redshift survey measure dark energy clustering?

(abridged) A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales, which carries an invaluable information on horizon-scale physics complementarily to the cosmic microwave background (CMB). Assuming the planned survey consisting of z~1 and z~3 surveys with areas of 2000 and 300 square degrees, respectively, we study the prospects for probing dark energy clustering from the measured galaxy power spectrum, assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c_e in the context of an adiabatic cold dark matter dominated model. The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon, and the enhancement is sensitive to redshift evolution of the net dark energy density, i.e. the equation of state. We find that the galaxy survey, when combined with Planck, can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model (c_e=1), when c_e<0.04 (0.02) in the case of the constant equation of state w_0=-0.9 (-0.95). An ultimate full-sky survey of z~1 galaxies allows the detection when c_e<0.08 (0.04) for w_0=0.9 (-0.95). We also investigate a degeneracy between the dark energy clustering and the non-relativistic neutrinos implied from the neutrino oscillation experiments, because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey. It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences, where dark energy clustering is apparent only at low redshifts z<1.Comment: 14 pages, 7 figures; minor changes to match the published versio