On-line relational SOM for dissimilarity data

International audienceIn some applications and in order to address real world situations better, data may be more complex than simple vectors. In some examples, they can be known through their pairwise dissimilarities only. Several variants of the Self Organizing Map algorithm were introduced to generalize the original algorithm to this framework. Whereas median SOM is based on a rough representation of the prototypes, relational SOM allows representing these prototypes by a virtual combination of all elements in the data set. However, this latter approach suffers from two main drawbacks. First, its complexity can be large. Second, only a batch version of this algorithm has been studied so far and it often provides results having a bad topographic organization. In this article, an on-line version of relational SOM is described and justified. The algorithm is tested on several datasets, including categorical data and graphs, and compared with the batch version and with other SOM algorithms for non vector data

Use of ERTS-1 data to access and monitor change in the west side of the San Joaquin Valley and central coastal zone of California

There are no author-identified significant results in this report

Landau diamagnetism of a weakly bound muonium atom

The ionization with temperature of weakly bound muonium atoms in undoped CdS has been studied using the technique of muon spin relaxation in a transverse magnetic field of 10 mT. For this atom the Coulomb binding energy between the muon and the electron is sufficiently small that the Landau diamagnetic term determines the magnetic behavior of the system: due to the diamagnetic interaction the muon precession in a transverse magnetic field exhibits a frequency shift of approximately 0.5% around the ionization temperature.http://www.sciencedirect.com/science/article/B6TVM-448FTXD-1/1/e6a2420c40c0e5e534a3e5d0f052d41

Environment, Ram Pressure, and Shell Formation in HoII

Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII, a prototype galaxy for studies of shell formation, are presented. HI is detected to radii over 16' or 4 R_25, and M_HI=6.44x10^8 M_sun. The total HI map has a comet-like appearance suggesting that HoII is affected by ram pressure from an intragroup medium (IGM). A rotation curve corrected for asymmetric drift was derived and an analysis of the mass distribution yields a total mass 6.3x10^9 M_sun, of which about 80% is dark. HoII lies northeast of the M81 group's core, along with Kar52 (M81dwA) and UGC4483. No signs of interaction are observed and it is argued that HoII is part of the NGC2403 subgroup, infalling towards M81. A case is made for ram pressure stripping and an IGM in the M81 group. Stripping of the disk outer parts would require an IGM density n_IGM>=4.0x10^-6 atoms/cm^3 at the location of HoII. This corresponds to 1% of the virial mass of the group uniformly distributed over a volume just enclosing HoII and is consistent with the X-ray properties of small groups. It is argued that existing observations of HoII do not support self-propagating star formation scenarios, whereby the HI holes and shells are created by supernova explosions and stellar winds. Many HI holes are located in low surface density regions of the disk, where no star formation is expected or observed. Ram pressure has the capacity to enlarge preexisting holes and lower their creation energies, helping to bridge the gap between the observed star formation rate and that required to create the holes. (abridged)Comment: 43 pages, including 7 figures. 4 figures available as JPEG only. Complete manuscript including full resolution figures available at http://www.strw.leidenuniv.nl/~bureau/pub_list.html . Accepted for publication in The Astronomical Journa

The O-Na and Mg-Al Anticorrelations in Turn-Off and early Subgiants in Globular Clusters

High dispersion spectra (R>40,000) for a quite large number of stars at the main sequence turn-off and at the base of the subgiant branch in NGC6397 and NGC6752 were obtained with the UVES on Kueyen (VLT UT2). The [Fe/H] values we found are -2.03+/-0.02+/-0.04 and -1.42+/-0.02+/-0.04 for NGC6397 and NGC6752 respectively, where the first error bars refer to internal errors and the second ones to systematic errors. In both clusters the [Fe/H] obtained for TO-stars agree perfectly (within a few per cents) with that obtained for stars at the base of the RGB. The [O/Fe]=0.21+/-0.05 value we obtain for NGC6397 is quite low, but it agrees with previous results obtained for giants in this cluster; also, the star-to-star scatter in both O and Fe is very small, indicating that this small mass cluster is chemically very homogenous. On the other side, our results show clearly and for the first time that the O-Na anticorrelation (up to now seen only for stars on the red giant branches of globular clusters) is present among unevolved stars in the globular cluster NGC6752, a more massive cluster than NGC6397. A similar anticorrelation is present also for Mg and Al, and C and N. It is very difficult to explain the observed Na-O, and Mg-Al anticorrelation in NGC6752 stars by a deep mixing scenario; we think it requires some non internal mechanism.Comment: 20 pages, A&A Latex, including 7 .ps figures, tex-macro aa.cls, uses psfig.tex. submitted to Astronomy & Astrophysic

Colligative properties of solutions: I. Fixed concentrations

Using the formalism of rigorous statistical mechanics, we study the phenomena of phase separation and freezing-point depression upon freezing of solutions. Specifically, we devise an Ising-based model of a solvent-solute system and show that, in the ensemble with a fixed amount of solute, a macroscopic phase separation occurs in an interval of values of the chemical potential of the solvent. The boundaries of the phase separation domain in the phase diagram are characterized and shown to asymptotically agree with the formulas used in heuristic analyses of freezing point depression. The limit of infinitesimal concentrations is described in a subsequent paper.Comment: 28 pages, 1 fig; see also math-ph/0407035 (both to appear in JSP

Spectropolarimetry of R Coronae Borealis in 1998--2003: Discovery of Transient Polarization at Maximum Brightness

We present an extended optical spectropolarimetry of R CrB from 1998 January to 2003 September. The polarization was almost constant in the phase of maximum brightness, being consistent with past observations. We detected, however, temporal changes of polarization ($\sim 0.5$ %) in 2001 March and August, which were the first detection of large polarization variability in R CrB near maximum brightness. The amplitude and the position angle of the `transient polarization' were almost constant with wavelength in both two events. There was a difference by about 20 degrees in the position angle between the two events. Each event could be explained by light scattering due to short-lived dust puff occasionally ejected off the line of sight. The flatness of the polarization against the wavelength suggests that the scatterer is a mixture of dust grains having various sizes. The rapid growth and fading of the transient polarization favors the phenomenological model of dust formation near the stellar photosphere (e.g., within two stellar radii) proposed for the time evolution of brightness and chromospheric emission lines during deeply declining periods, although the fading timescale can hardly be explained by a simple dispersal of expanding dust puff with a velocity of $\sim 200-350$ km s $^{-1}$. Higher expansion velocity or some mechanism to destroy the dust grains should be needed.Comment: 22 pages, 10 figures, accepted for publication in A

The effect of pre-shot routines on golf wedge shot performance

The objective of this study was to examine the effect of pre-performance routines among golfers of low skill and non-golfers on wedge golf shot performance. The intervention strategies involved a physical skill and cognitive-behavioral routine program, as well as a physical skills-only program. Performance was measured on a pre-intervention test, postintervention test, and following a period of time without treatment, and involved wedge shots being played from distances of 40, 50, and 60 m from a target. Participants in this study (N = 68) were assigned to either a golfer or non-golfer group. Participants in the treatment groups attended 2 practice sessions per week during the acquisition phase. A variable practice design was incorporated during the intervention phase. Non-golfers in both intervention groups improved performance following the acquisition phase and maintained these levels of performance in the retention test. Greater improvements in performance were found in the non-golfer physical skills and cognitive-behavioral routine group. The non-golfer physical skills and cognitive-behavioral routine group was the only group to realize significant improvements in performance when comparing initial test performance measures to post-intervention and retention test performance measures across all test distances. Although the golfer treatment groups had consistent improvement in performance measures following the intervention phase, these improvements did not reach statistical significance in the majority of cases

‘… a metal conducts and a non-metal doesn't’

In a letter to one of the authors, Sir Nevill Mott, then in his tenth decade, highlighted the fact that the statement ‘… a metal conducts, and a non-metal doesn’t’ can be true only at the absolute zero of temperature, T=0 K. But, of course, experimental studies of metals, non-metals and, indeed, the electronic and thermodynamic transition between these canonical states of matter must always occur above T=0 K, and, in many important cases, for temperatures far above the absolute zero. Here, we review the issues—theoretical and experimental—attendant on studies of the metal to non-metal transition in doped semiconductors at temperatures close to absolute zero (T=0.03 K) and fluid chemical elements at temperatures far above absolute zero (T>1000 K)

Enhanced error estimator based on a nearly equilibrated moving least squares recovery technique for FEM and XFEM

In this paper a new technique aimed to obtain accurate estimates of the error in energy norm using a moving least squares (MLS) recovery-based procedure is presented. We explore the capabilities of a recovery technique based on an enhanced MLS fitting, which directly provides continuous interpolated fields, to obtain estimates of the error in energy norm as an alternative to the superconvergent patch recovery (SPR). Boundary equilibrium is enforced using a nearest point approach that modifies the MLS functional. Lagrange multipliers are used to impose a nearly exact satisfaction of the internal equilibrium equation. The numerical results show the high accuracy of the proposed error estimator