Quantum Statistics: Is there an effective fermion repulsion or boson attraction?

Physicists often claim that there is an effective repulsion between fermions, implied by the Pauli principle, and a corresponding effective attraction between bosons. We examine the origins of such exchange force ideas, the validity for them, and the areas where they are highly misleading. We propose that future explanations of quantum statistics should avoid the idea of a effective force completely and replace it with more appropriate physical insights, some of which are suggested here.Comment: 26 pages, 3 figures. Submitted to American Journal of Physic

Heavy Quark Lifetimes, Mixing and CP Violation

This paper emphasizes four topics that represent some of the year's highlights in heavy quark physics. First of all, a review is given of charm lifetime measurements and how they lead to better understanding of the mechanisms of charm decay. Secondly, the CLEO collaboration's new search for charm mixing is reported, which significantly extends the search for new physics in that sector. Thirdly, important updates in Bs mixing are summarized, which result in a new limit on the mass difference, and which further constrain the unitarity triangle. Finally, the first efforts to measure CP violation in the B system are discussed. Results are shown for the CDF and ALEPH measurements of sin(2beta), as well as the CLEO branching fraction measurements of B-->Kpi,pipi, which have implications for future measurements of alpha.Comment: 25 pages, 15 figures. Talk given at the XIX International Symposium on Lepton and Photon Interactions, Stanford University, August 9-14, 199

Chromosomal aberrations in a natural population of chironomus tentans exposed to chronic low-level environmental radiation

The salivary gland chromosomes of Chironomus tentans larvae collected from White Oak Creek, an area contaminated by radioactive waste from the Oak Ridge National Laboratory, and from six uncontaminated areas were examined for chromosomal aberrations. White Oak Creek populations were exposed to absorbed doses as high as 230 rads per year or about 1000 times background. Chromosomal maps were constructed to make a general comparison of the banding pattern of the salivary chromosomes of the C. tentans in the East Tennessee area with those of Canada and Europe. These maps were used as a reference in scoring aberrations. Fifteen different chromosomal aberrations were found in 365 larvae taken from the irradiated population as compared with five different aberrations observed in 356 larvae from six control populations, but the mean number of aberrations per larva did not differ in any of the populations. The quantitative amount of heterozygosity was essentially the same in the irradiated and the control population, but there were three times the variety of chromosomal aberrations found in the irradiated area. From this evidence it was concluded that chronic low-level irradiation from radioactive waste was increasing the variability of chromosomal aberrations without significantly increasing the frequency. It was also concluded that chromosomal polymorphism can be maintained in a natural population without superiority of the heterozygous individuals. (C.H.

The Role of CP violation in D0 anti-D0 Mixing

In current searches for D0 anti-D0 mixing, the time evolution of ``wrong-sign'' decays is used to distinguish between a potential mixing signal and the dominant background from doubly-Cabibbo-suppressed decays. A term proportional to $\Delta Mt$ in the expression for the time evolution is often neglected in theoretical discussions and experimental analyses of these processes. We emphasize that, in general, this term does not vanish even in the case of CP invariance. Furthermore, CP invariance is likely to be violated if the rate of D0 anti-D0 mixing is close to the experimental bound. The consequence of either of these two facts is that the strongest existing measured bound is not applicable for constraining New Physics.Comment: 14 pages, uuencoded gzip-compressed postscript (84 kB

Interpreting experimental bounds on D^0 - \bar{D^0} mixing in the presence of CP violation

We analyse the most recent experimental data regarding D^0 - \bar{D^0} mixing, allowing for CP violation. We focus on the dispersive part of the mixing amplitude, M^D_{12}, which is sensitive to new physics contributions. We obtain a constraint on the mixing amplitude: |M^D_{12}| < 6.2\times 10^{-11} MeV at 95% C.L. . This constraint is weaker by a factor of about three than the one which is obtained when no CP violation is assumed.Comment: 9 pages, revtex4; One reference updated, one reference added, footnote 3 correcte

Spitzer Observations of Low Luminosity Isolated and Low Surface Brightness Galaxies

We examine the infrared properties of five low surface brightness galaxies (LSBGs) and compare them with related but higher surface brightness galaxies, using Spitzer Space Telescope images and spectra. All the LSBGs are detected in the 3.6 and 4.5um bands, representing the stellar population. All but one are detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic molecules, though many are faint or point-like at these wavelengths. Detections of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in morphology and brightness, with only two detections at 160um, resulting in highly varied spectral energy distributions. Consistent with previous expectations for these galaxies, we find that detectable dust components exist for only some LSBGs, with the strength of dust emission dependent on the existence of bright star forming regions. However, the far-infrared emission may be relatively weak compared with normal star-forming galaxies.Comment: 20 pages, 8 figures, accepted to Ap

IR observations of MS 1054-03: Star Formation and its Evolution in Rich Galaxy Clusters

We study the infrared (IR) properties of galaxies in the cluster MS 1054-03 at z=0.83 by combining MIPS 24 micron data with spectra of more than 400 galaxies and a very deep K-band selected catalog. 19 IR cluster members are selected spectroscopically, and an additional 15 are selected by their photometric redshifts. We derive the IR luminosity function of the cluster and find strong evolution compared to the similar-mass Coma cluster. The best fitting Schechter function gives L*_{IR}=11.49 +0.30/-0.29 L_sun with a fixed faint end slope, about one order of magnitude larger than that in Coma. The rate of evolution of the IR luminosity from Coma to MS 1054-03 is consistent with that found in field galaxies, and it suggests that some internal mechanism, e.g., the consumption of the gas fuel, is responsible for the general decline of the cosmic star formation rate (SFR) in different environments. The mass-normalized integrated SFR within 0.5R_200 in MS 1054-03 also shows evolution compared with other rich clusters at lower redshifts, but the trend is less conclusive if the mass selection effect is considered. A nonnegligible fraction (13%) of cluster members, are forming stars actively and the overdensity of IR galaxies is about 20 compared to the field. It is unlikely that clusters only passively accrete star forming galaxies from the surrounding fields and have their star formation quenched quickly afterward; instead, many cluster galaxies still have large amounts of gas, and their star formation may be enhanced by the interaction with the cluster.Comment: 49 pages, 9 figures, accepted by Ap

Dcse Estimation and Prediction of Radiation Effects on Aquatic Biota Resulting from Radioactive Releases .from the Nuclear Fuel Cycle*

ABSTRACT -NOTICE vepott was rnir . prepared as an accou.T of work S&apos;Cut efponsibuity for the accuracy, completeness « uJulnas of any information, apparatus, product o process disclosed, or represents that its use would not d iht process disclo, p infringe privately owned lights. Aquatic organisms are exposed to radionuclides released to the environment during various steps of the nuclear fuel cycle. Routine releases from these processes are limited in compliance with technical specifications, requirements of federal regulations. These regulations reflect I.C.R.P. recommendations which are designed to provide an environment considered safe for man. It is generally accepted that aquatic organisms will not receive damaging external radiation doses in such environments; however, because of possible bioaccunulation of radionuclides there is concern that aquatic organisms might be adversely affected &apos;ay internal doses. The objectives of this paper are: (1) to estimate the radiation dose received by aquatic biota from the different processes and determine the major dose-contributing radionuclides, and (2) to assess the impact of estimated doses on aquatic biota. Dose estimates are made by using radionuclide concentration measured in the liquid effiuents of representative facilities. Where measurements of concentrations are rot available, predicted radioactive releases to the aquatic environment are used for dose calculations. Although radioactive releases from reactors used to generate electrical energy have received the most attention, and are the best documented, this evaluation indicates the potential for a greater radiation dose to aquatic biota from the nuclear fuel supply facilities (i.e., mining and milling).. The effects of chronic low-level radiation on aquatic organisms are discussed from somatic and genetic viewpoints. Based on the body of radiobiological evidence accumulated up to the present time, no significant deleterious effects are predicted for populations of aquatic organisms exposed to the estimated dose rates resulting from routine releases from conversion, enrichment, fabrication, reactors and reporcessing facilities. At the doses estimated for milling and mining operations it would be difficult to detect radiation effects on aquatic populations; however, the significance of such radiation exposures to aquatic populations cannot be fully evaluated without further research on effects of chronic low-level radiation

Sequence-Specific, Nanomolar Peptide Binding via Cucurbit[8]uril-Induced Folding and Inclusion of Neighboring Side Chains

This paper describes the molecular recognition of the tripeptide Tyr-Leu-Ala by the synthetic receptor cucurbit[8]uril (Q8) in aqueous buffer with nanomolar affinity and exceptional specificity. This combination of characteristics, which also applies to antibodies, is desirable for applications in biochemistry and biotechnology but has eluded supramolecular chemists for decades. Building on prior knowledge that Q8 binds to peptides with N-terminal aromatic residues, a library screen of 105 peptides was designed to test the effects of residues adjacent to N-terminal Trp, Phe, or Tyr. The screen used tetramethylbenzobis(imidazolium) (MBBI) as a fluorescent indicator and resulted in the unexpected discovery that MBBI can serve not only as a turn-off sensor via the simultaneous inclusion of a Trp residue but also as a turn-on sensor via the competitive displacement of MBBI upon binding of Phe- or Tyr-terminated peptides. The unusual fluorescence response of the Tyr series prompted further investigation by 1H NMR spectroscopy, electrospray ionization mass spectrometry, and isothermal titration calorimetry. From these studies, a novel binding motif was discovered in which only 1 equiv of peptide binds to Q8, and the side chains of both the N-terminal Tyr residue and its immediate neighbor bind within the Q8 cavity. For the peptide Tyr-Leu-Ala, the equilibrium dissociation constant value is 7.2 nM, whereas that of its sequence isomer Tyr-Ala-Leu is 34 μM. The high stability, recyclability, and low cost of Q8 combined with the straightforward incorporation of Tyr-Leu-Ala into recombinant proteins should make this system attractive for the development of biological applications