The Properties of Field Elliptical Galaxies at Intermediate Redshift. I: Empirical Scaling Laws

We present measurements of the Fundamental Plane (FP) parameters (the effective radius, the mean effective surface brightness, and the central velocity dispersion) of six field elliptical galaxies at intermediate redshift. The imaging is taken from the Medium Deep Survey of the Hubble Space Telescope, while the kinematical data are obtained from long-slit spectroscopy using the 3.6-m ESO telescope. The Fundamental Plane appears well defined in the field even at redshift $\approx$ 0.3. The data show a shift in the FP zero point with respect to the local relation, possibly indicating modest evolution, consistent with the result found for intermediate redshift cluster samples. The FP slopes derived for our field data, plus other cluster ellipticals at intermediate redshift taken from the literature, differ from the local ones, but are still consistent with the interpretation of the FP as a result of homology, of the virial theorem and of the existence of a relation between luminosity and mass, $L \propto M^{\eta}$. We also derive the surface brightness vs. effective radius relation for nine galaxies with redshift up to $z \approx0.6$, and data from the literature; the evolution that can be inferred is consistent with what is found using the FP.Comment: 17 pages, including 9 figures, MNRAS, accepte

Mathisson's helical motions for a spinning particle --- are they unphysical?

It has been asserted in the literature that Mathisson's helical motions are unphysical, with the argument that their radius can be arbitrarily large. We revisit Mathisson's helical motions of a free spinning particle, and observe that such statement is unfounded. Their radius is finite and confined to the disk of centroids. We argue that the helical motions are perfectly valid and physically equivalent descriptions of the motion of a spinning body, the difference between them being the choice of the representative point of the particle, thus a gauge choice. We discuss the kinematical explanation of these motions, and we dynamically interpret them through the concept of hidden momentum. We also show that, contrary to previous claims, the frequency of the helical motions coincides, even in the relativistic limit, with the zitterbewegung frequency of the Dirac equation for the electron

The clock paradox in a static homogeneous gravitational field

The gedanken experiment of the clock paradox is solved exactly using the general relativistic equations for a static homogeneous gravitational field. We demonstrate that the general and special relativistic clock paradox solutions are identical and in particular that they are identical for finite acceleration. Practical expressions are obtained for proper time and coordinate time by using the destination distance as the key observable parameter. This solution provides a formal demonstration of the identity between the special and general relativistic clock paradox with finite acceleration and where proper time is assumed to be the same in both formalisms. By solving the equations of motion for a freely falling clock in a static homogeneous field elapsed times are calculated for realistic journeys to the stars.Comment: Revision: Posted with the caption included with the figure

The effects of salinity and temperature on the development and survival of fish parasites

In brackish water the variety of marine and freshwater parasite species is considerably reduced. The distribution in brackish water of most marine endoparasites is restricted by the salinity tolerance of their hosts, most of the parasite species are more tolerant than their hosts. The influence of salinity and temperature on nine species has been examined; first stage larvae of Contracaecum aduncum develop in 0-32‰ salinity; Cryptocotyle lingua proved to be infective at salinities down to 4‰. The greatest resistance was found in Anisakis larvae from herring Clupea harengus, which survived for more than half a year. Parasites in the fish intestines appear to be unaffected by changing water salinities, as the osmolarity in the intestines stays nearly constant. Marine ectoparasites (Acanthochondria depressa, Lepeophtheirus pectoralis) survive about three times longer than freshwater species (Piscicola geometra, Argulus foliaceus) when salinity is 16‰. High temperature increases the effects of adverse salinities on parasites. There is evidence that none of these ecto-parasitic species can develop within the range of 7-20‰ salinity

Pairing correlations. Part 1: description of odd nuclei in mean-field theories

In order to extract informations on pairing correlations in nuclei from experimental mass differences, the different contributions to odd-even mass differences are investigated within the Skyrme HFB method. In this first paper, the description of odd nuclei within HFB is discussed since it is the key point for the understanding of the above mentioned contributions. To go from an even nucleus to an odd one, the advantage of a two steps process is demonstrated and its physical content is discussed. New results concerning time-reversal symmetry breaking in odd-nuclei are also reported. PACS: 21.10Dr; 21.10.Hw; 21.30.-x. Keywords: Mean-field theories; Pairing correlations; odd nuclei;Comment: 34 pages, 8 figures. Submitted to Phys. Rev.

Reply To "comment On 'photoionization Of Helium Atoms Irradiated With Intense Vacuum Ultraviolet Free-electron Laser Light. Part I. Experimental Study Of Multiphoton And Single-photon Processes'"

We do not agree with the conclusion of the Comment by Charalambidis questioning our observation of two-photon ionization of helium by intense radiation with 13 eV photons from a vuv free-electron laser. Two-photon ionization is clearly established by the detection of low-energy photoelectrons at ∼1.7 eV, which agrees very well with the expected energy for a two-photon ionization process. © 2006 The American Physical Society.743Laarmann, T., De Castro, A.R.B., Schulz, J., Wabnitz, H., Möller, T., (2005) Phys. Rev. A, 72, p. 023409. , PLRAAN. 1050-2947. 10.1103/PhysRevA.72.023409Ayvazyan, V., Baboi, N., Bohnet, I., Brinkmann, R., Castellano, M., Castro, P., Catani, L., Zapfe, K., (2002) Phys. Rev. Lett., 88, p. 104802. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.88.104802Ayvazyan, V., Baboi, N., Bähr, J., Balandin, V., Beutner, B., Brandt, A., Bohnet, I., Schreiber H, -J., (2006) Eur. Phys. J. D, 37, p. 297. , EPJDF6. 1434-6060. 10.1140/epjd/e2005-00308-1Wabnitz, H., Bittner, L., De Castro, A.R.B., Döhrmann, R., Gürtler, P., Laarmann, T., Laasch, W., Yurkov, M., (2002) Nature (London), 420, p. 482. , NATUAS. 0028-0836. 10.1038/nature01197Laarmann, T., De Castro, A.R.B., Gürtler, P., Laasch, W., Schulz, J., Wabnitz, H., Möller, T., (2004) Phys. Rev. Lett., 92, p. 143401. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.92.143401Laarmann, T., Rusek, M., Wabnitz, H., Schulz, J., De Castro, A.R.B., Gürtler, P., Laasch, W., Möller, T., (2005) Phys. Rev. Lett., 95, p. 063402. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.95.063402Wabnitz, H., De Castro, A.R.B., Gürtler, P., Laarmann, T., Laasch, W., Schulz, J., Möller, T., (2005) Phys. Rev. Lett., 94, p. 023001. , PRLTAO. 0031-9007. 10.1103/PhysRevLett.94.023001Santra, R., Greene, C.H., (2004) Phys. Rev. A, 70, p. 053401. , PLRAAN 1050-2947 10.1103/PhysRevA.70.053401Tzallas, P., Charalambidis, D., Papadogiannis, N.A., Witte, K., Tsakiris, G.D., (2003) Nature (London), 426, p. 267. , NATUAS 0028-0836 10.1038/nature02091Papadogiannis, N.A., Nikolopoulos, L.A.A., Charalambidis, D., Tsakiris, G.D., Tzallas, P., Witte, K., (2003) Appl. Phys. B, 76, p. 721. , APDOEM 0946-2171Papadogiannis, N.A., Nikolopoulos, L.A.A., Charalambidis, D., Tsakiris, G.D., Tzallas, P., Witte, K., (2003) Phys. Rev. Lett., 90, p. 133902. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.133902De Castro, A.R.B., Laarmann, T., Schulz, J., Wabnitz, H., Möller, T., (2005) Phys. Rev. A, 72, p. 023410. , PLRAAN. 1050-2947. 10.1103/PhysRevA.72.02341

Covariant Uniform Acceleration

We show that standard Relativistic Dynamics Equation F=dp/d\tau is only partially covariant. To achieve full Lorentz covariance, we replace the four-force F by a rank 2 antisymmetric tensor acting on the four-velocity. By taking this tensor to be constant, we obtain a covariant definition of uniformly accelerated motion. We compute explicit solutions for uniformly accelerated motion which are divided into four types: null, linear, rotational, and general. For null acceleration, the worldline is cubic in the time. Linear acceleration covariantly extends 1D hyperbolic motion, while rotational acceleration covariantly extends pure rotational motion. We use Generalized Fermi-Walker transport to construct a uniformly accelerated family of inertial frames which are instantaneously comoving to a uniformly accelerated observer. We explain the connection between our approach and that of Mashhoon. We show that our solutions of uniformly accelerated motion have constant acceleration in the comoving frame. Assuming the Weak Hypothesis of Locality, we obtain local spacetime transformations from a uniformly accelerated frame K' to an inertial frame K. The spacetime transformations between two uniformly accelerated frames with the same acceleration are Lorentz. We compute the metric at an arbitrary point of a uniformly accelerated frame. We obtain velocity and acceleration transformations from a uniformly accelerated system K' to an inertial frame K. We derive the general formula for the time dilation between accelerated clocks. We obtain a formula for the angular velocity of a uniformly accelerated object. Every rest point of K' is uniformly accelerated, and its acceleration is a function of the observer's acceleration and its position. We obtain an interpretation of the Lorentz-Abraham-Dirac equation as an acceleration transformation from K' to K.Comment: 36 page

EVALUATION OF SINGLE TRACKS OF 17-4PH STEEL MANUFACTURED AT DIFFERENT POWER DENSITIES AND SCANNING SPEEDS BY SELECTIVE LASER MELTING

In Selective Laser Melting, the initial units produced are single tracks that overlap to create a single layer; from the sequence of layers, a 3D object is manufactured. The properties of the parts produced by SLM depend heavily on the properties of each single track and each layer formed by these tracks. This study evaluates the effect of processing parameters on the geometrical characteristics of single tracks manufactured from 17-4PH stainless steel powder. A single-mode continuous-wave ytterbium fibre laser was used to manufacture single tracks at laser powers in the range of 100-300 W with a constant spot size of ∼80μm. The single tracks produced were subjected to standard metallographic preparation techniques for further analysis with an optical microscope. Deep molten pool shapes were observed at low scan speeds, while shallow molten pool shapes were observed at high scan speeds. At higher laser power densities, under-cutting and humping effects were also observed. The dimensions of single tracks processed without powder generally decrease with increasing scan speed at constant laser power. However, the geometrical features of the single tracks processed with powder revealed pronounced irregularities believed to be caused by non-homogeneity in the deposited powder layer

A Composite HST Spectrum of Quasars

We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z > 0.33. The spectrum covers the wavelengths between 350 and 3000 A in the rest frame. There is a significant steepening of the continuum slope around 1050 A. The continuum between 1050 and 2200 A can be modeled as a power law with alpha = -0.99. For the full sample the power-law index in the extreme ultraviolet (EUV) between 350 and 1050 A is alpha = -1.96. The continuum flux in the wavelengths near the Lyman limit shows a depression of about 10 percent. The break in the power-law index and the slight depression of the continuum near the Lyman limit are features expected in Comptonized accretion-disk spectra.Comment: 10 figures To appear in the February 1, 1997, issue of the Ap.

The neural correlates of subjectively perceived and passively matched loudness perception in auditory phantom perception

International audienceIntroduction: A fundamental question in phantom perception is determining whether the brain creates a network that represents the sound intensity of the auditory phantom as measured by tinnitus matching (in dB), or whether the phantom perception is actually only a representation of the subjectively perceived loudness. Methods: In tinnitus patients, tinnitus loudness was tested in two ways, by a numeric rating scale for subjectively perceived loudness and a more objective tinnitus-matching test, albeit it is still a subjective measure. Results: Passively matched tinnitus does not correlate with subjective numeric rating scale, and has no electrophysiological correlates. Subjective loudness, in a whole-brain analysis, is correlated with activity in the left anterior insula (alpha), the rostral/dorsal anterior cingulate cortex (beta), and the left parahip-pocampus (gamma). A ROI analysis finds correlations with the auditory cortex (high beta and gamma) as well. The theta band links gamma band activity in the auditory cortex and parahippocampus via theta–gamma nesting. Conclusions: Apparently the brain generates a network that represents subjectively perceived tinnitus loudness only, which is context dependent. The subjective loudness network consists of the anterior cingulate/insula, the parahippocam-pus, and the auditory cortex. The gamma band activity in the parahippocampus and the auditory cortex is functionally linked via theta–gamma nested lagged phase synchronization