Discerning Elementary Particles

We extend the quantum-mechanical results of Muller & Saunders (2008) establishing the weak discernibility of an arbitrary number of similar fermions in finite-dimensional Hilbert-spaces in two ways: (a) from fermions to bosons for all finite-dimensional Hilbert-spaces; and (b) from finite-dimensional to infinite-dimensional Hilbert-spaces for all elementary particles. In both cases this is performed using operators whose physical significance is beyond doubt.This confutes the currently dominant view that (A) the quantum-mechanical description of similar particles conflicts with Leibniz's Principle of the Identity of Indiscernibles (PII); and that (B) the only way to save PII is by adopting some pre-Kantian metaphysical notion such as Scotusian haecceittas or Adamsian primitive thisness. We take sides with Muller & Saunders (2008) against this currently dominant view, which has been expounded and defended by, among others, Schr\"odinger, Margenau, Cortes, Dalla Chiara, Di Francia, Redhead, French, Teller, Butterfield, Mittelstaedt, Giuntini, Castellani, Krause and Huggett.Comment: Final Version. To appear in Philosophy of Science, July 200

Hyposplenism in gastro-intestinal disease

The hazards of living without a spleen were recognised by the paediatricians in the early 1960’s when they focussed attention on the syndrome of fulminant sepsis, often due to pneumococcal infection, occurring in young children within the first two years of splenectomy. The danger of post-splenectomy sepsis (PSS) extends into adult life and splenectomised patients remain at risk 10, 20 and even 30 years after the operation. Problems following splenectomy may just be the tip of the iceberg. It is clear that many other diseases are associated with impaired splenic function in the presence of intact spleens.peer-reviewe

Morphological evidence for a sea-ice origin for Elysium Planitia platy terrain

Abstract not available

Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX

We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameter chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by Liquid Chromatography at the Point of Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA-b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur.Comment: 32 pages, 16 figures and 4 tables submitted to Journal of Interface and Colloidal Scienc

A survey of HC_3N in extragalactic sources: Is HC_3N a tracer of activity in ULIRGs?

Context. HC_3N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments. Aims. To present the first extragalactic survey of HC_3N, when combining earlier data from the literature with six new single-dish detections, and to compare HC_3N with other molecular tracers (HCN, HNC), as well as other properties (silicate absorption strength, IR flux density ratios, C_(II) flux, and megamaser activity). Methods. We present mm IRAM 30 m, OSO 20 m, and SEST observations of HC_3N rotational lines (mainly the J = 10–9 transition) and of the J = 1–0 transitions of HCN and HNC. Our combined HC_3N data account for 13 galaxies (excluding the upper limits reported for the non-detections), while we have HCN and HNC data for more than 20 galaxies. Results. A preliminary definition “HC_3N-luminous galaxy” is made based upon the HC_3N/HCN ratio. Most (~80%) HC_3N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (~60% or more) of the HC3N-luminous galaxies in the sample present OH mega- or strong kilomaser activity. A possible explanation is that both HC_3N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC_3N. A high silicate absorption strength is also found in several of the HC_3N-luminous objects, which may help the HC3N to survive. Finally, we find that a high HC_3N/HCN ratio is related to a high dust temperature and a low C_(II) flux

Infrared Search for Young Stars in HI High-velocity Clouds

We have searched the IRAS Point Source Catalog and HIRES maps for young stellar objects (YSOs) in the direction of five \HI high-velocity clouds (HVCs). In agreement with optical searches in the halo, no evidence was found for extensive star-forming activity inside the high-latitude HVCs. Specifically, we have found no signs of star formation or YSOs in the direction of the A IV cloud or in the very-high-velocity clouds HVC~110-7-465 and HVC~114-10-440. We have identified only one young star in the direction of the M~I.1 cloud, which shows almost perfect alignment with a knot of \HI emission. Because of the small number of early-type stars observed in the halo, the probability for such a positional coincidence is low; thus, this young star appears to be physically associated with the M~I.1 cloud. We have also identified a good YSO candidate in the \HI shell-like structure observed in the core region of the low-latitude cloud complex H (HVC~131+1-200). This region could be a supernova remnant with several other YSO candidates formed along the shock front produced by the explosion. In agreement with recent theoretical estimates, these results point to a low but significant star-formation rate in intermediate and high Galactic latitude HVCs. For M~I.1 in particular, we estimate that the efficiency of the star-formation process is M(YSO)/M(\HI)\ga 10^{-4}-10^{-3} by mass. Such efficiency is sufficient to account for (a) the existence of the few young blue stars whose ages imply that they were born in the Galactic halo, and (b) the nonprimordial metallicities inferred for some HVCs if their metal content proves to be low.Comment: 9 pages, 4 JPEG figures. PostScript figures available from author

Out of equilibrium quantum field dynamics of an initial thermal state after a change in the external field

The effects of the initial temperature in the out of equilibrium quantum field dynamics in the presence of an homogeneous external field are investigated. We consider an initial thermal state of temperature T for a constant external field J. A subsequent sign flip of the external field, J to -J, gives rise to an out of equilibrium nonperturbative quantum field dynamics. The dynamics is studied here for the symmetry broken lambda(Phi^2)^2 scalar N component field theory in the large N limit. We find a dynamical effective potential for the expectation value that helps to understand the dynamics. The dynamics presents two regimes defined by the presence or absence of a temporal trapping close to the metastable equilibrium position of the potential. The two regimes are separated by a critical value of the external field that depends on the initial temperature. The temporal trapping is shorter for larger initial temperatures or larger external fields. Parametric resonances and spinodal instabilities amplify the quantum fluctuations in the field components transverse to the external field. When there is a temporal trapping this is the main mechanism that allows the system to escape from the metastable state for large N. Subsequently backreaction stops the growth of the quantum fluctuations and the system enters a quasiperiodic regime.Comment: LaTeX, 19 pages, 12 .eps figures, improved version to appear in Phys Rev

Non-Gaussian statistics and extreme waves in a nonlinear optical cavity

A unidirectional optical oscillator is built by using a liquid crystal light-valve that couples a pump beam with the modes of a nearly spherical cavity. For sufficiently high pump intensity, the cavity field presents a complex spatio-temporal dynamics, accompanied by the emission of extreme waves and large deviations from the Gaussian statistics. We identify a mechanism of spatial symmetry breaking, due to a hypercycle-type amplification through the nonlocal coupling of the cavity field

High Ratio of 44Ti/56Ni in Cas A and Axisymmetric Collapse-Driven Supernova Explosion

The large abundance ratio of $^{44}Ti/^{56}Ni$ in Cas A is puzzling. In fact, the ratio seems to be larger than the theoretical constraint derived by Woosley & Hoffman (1991). However, this constraint is obtained on the assumption that the explosion is spherically symmetric, whereas Cas A is famous for the asymmetric form of the remnant. Recently, Nagataki et al. (1997) calculated the explosive nucleosynthesis of axisymmetrically deformed collapse-driven supernova. They reported that the ratio of $^{44}Ti/^{56}Ni$ was enhanced by the stronger alpha-rich freezeout in the polar region. In this paper, we apply these results to Cas A and examine whether this effect can explain the large amount of $^{44}Ti$ and the large ratio of $^{44}Ti/^{56}Ni$. We demonstrate that the conventional spherically symmetric explosion model can not explain the $^{44}$Ti mass produced in Cas A if its lifetime is shorter than $\sim$ 80 years and the intervening space is transparent to the gamma-ray line from the decay of $^{44}$Ti. On the other hand, we show the axisymmetric explosion models can solve the problem. We expect the same effect from a three dimensionally asymmetric explosion, since the stronger alpha-rich freezeout will also occur in that case in the region where the larger energy is deposited.Comment: 10 pages, LaTeX text and 3 postscript figure