Understanding the Observed Evolution of the Galaxy Luminosity Function from z=6-10 in the Context of Hierarchical Structure Formation

Recent observations of the Lyman-break galaxy (LBG) luminosity function (LF) from z~6-10 show a steep decline in abundance with increasing redshift. However, the LF is a convolution of the mass function of dark matter halos (HMF)--which also declines sharply over this redshift range--and the galaxy-formation physics that maps halo mass to galaxy luminosity. We consider the strong observed evolution in the LF from z~6-10 in this context and determine whether it can be explained solely by the behavior of the HMF. From z~6-8, we find a residual change in the physics of galaxy formation corresponding to a ~0.5 dex increase in the average luminosity of a halo of fixed mass. On the other hand, our analysis of recent LF measurements at z~10 shows that the paucity of detected galaxies is consistent with almost no change in the average luminosity at fixed halo mass from z~8. The LF slope also constrains the variation about this mean such that the luminosity of galaxies hosted by halos of the same mass are all within about an order-of-magnitude of each other. We show that these results are well-described by a simple model of galaxy formation in which cold-flow accretion is balanced by star formation and momentum-driven outflows. If galaxy formation proceeds in halos with masses down to 10^8 Msun, then such a model predicts that LBGs at z~10 should be able to maintain an ionized intergalactic medium as long as the ratio of the clumping factor to the ionizing escape fraction is C/f_esc < 10.Comment: 15 pages, 2 figures; results unchanged; accepted by JCA

Synthesis of high molecular weight water-soluble polymers as low-viscosity latex particles by RAFT aqueous dispersion polymerization in highly salty media

We report the synthesis of sterically-stabilized diblock copolymer particles at 20% w/w solids via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of N,N′-dimethylacrylamide (DMAC) in highly salty media (2.0 M (NH4)2SO4). This is achieved by selecting a well-known zwitterionic water-soluble polymer, poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC), to act as the salt-tolerant soluble precursor block. A relatively high degree of polymerization (DP) can be targeted for the salt-insoluble PDMAC block, which leads to the formation of a turbid free-flowing dispersion of PDMAC-core particles by a steric stabilization mechanism. 1H NMR spectroscopy studies indicate that relatively high DMAC conversions (>99%) can be achieved within a few hours at 30 °C. Aqueous GPC analysis indicates high blocking efficiencies and unimodal molecular weight distributions, although dispersities increase monotonically as higher degrees of polymerization (DPs) are targeted for the PDMAC block. Particle characterization techniques include dynamic light scattering (DLS) and electrophoretic light scattering (ELS) using a state-of-the-art instrument that enables accurate ζ potential measurements in a concentrated salt solution. 1H NMR spectroscopy studies confirm that dilution of the as-synthesized dispersions using deionized water lowers the background salt concentration and hence causes in situ molecular dissolution of the salt-intolerant PDMAC chains, which leads to a substantial thickening effect and the formation of transparent gels. Thus, this new polymerization-induced self-assembly (PISA) formulation enables high molecular weight water-soluble polymers to be prepared in a highly convenient, low-viscosity form. In principle, such aqueous PISA formulations are highly attractive: there are various commercial applications for high molecular weight water-soluble polymers, while the well-known negative aspects of using a RAFT agent (i.e., its cost, color, and malodor) are minimized when targeting such high DPs

Low-viscosity route to high-molecular-weight water-soluble polymers: exploiting the salt sensitivity of poly(N-acryloylmorpholine)

We report a new one-pot low-viscosity synthetic route to high molecular weight non-ionic water-soluble polymers based on polymerization-induced self-assembly (PISA). The RAFT aqueous dispersion polymerization of N-acryloylmorpholine (NAM) is conducted at 30 °C using a suitable redox initiator and a poly(2-hydroxyethyl acrylamide) (PHEAC) precursor in the presence of 0.60 M ammonium sulfate. This relatively low level of added electrolyte is sufficient to salt out the PNAM block, while steric stabilization is conferred by the relatively short salt-tolerant PHEAC block. A mean degree of polymerization (DP) of up to 6000 was targeted for the PNAM block, and high NAM conversions (>96%) were obtained in all cases. On dilution with deionized water, the as-synthesized sterically stabilized particles undergo dissociation to afford molecularly dissolved chains, as judged by dynamic light scattering and 1H NMR spectroscopy studies. DMF GPC analysis confirmed a high chain extension efficiency for the PHEAC precursor, but relatively broad molecular weight distributions were observed for the PHEAC-PNAM diblock copolymer chains (Mw/Mn > 1.9). This has been observed for many other PISA formulations when targeting high core-forming block DPs and is tentatively attributed to chain transfer to polymer, which is well known for polyacrylamide-based polymers. In fact, relatively high dispersities are actually desirable if such copolymers are to be used as viscosity modifiers because solution viscosity correlates closely with Mw. Static light scattering studies were also conducted, with a Zimm plot indicating an absolute Mw of approximately 2.5 × 106 g mol-1 when targeting a PNAM DP of 6000. Finally, it is emphasized that targeting such high DPs leads to a sulfur content for this latter formulation of just 23 ppm, which minimizes the cost, color, and malodor associated with the organosulfur RAFT agent

Superorbital expansion tube operation: estimates of flow conditions via numerical simulation

Two new operating conditions of the X3 superorbital expansion tube are studied experimentally and numerically. A two-stage numerical simulation is used to model the flow processes within the whole facility, from the compressed driver gas, through the initial shock-processing of the test gas and then through the unsteady expansion process to the final test flow state. Experimental measurements provide static pressure histories at particular points along the shock and acceleration tubes while the numerical simulations provide complementary information on gas density, temperature and composition. Operating condition properties such as shock speed are both observed in the experiment and produced as a result of the simulation are used to check the reliability of the numerical simulations

Search for the Rare Decay KL --> pi0 ee

The KTeV/E799 experiment at Fermilab has searched for the rare kaon decay KL--> pi0ee. This mode is expected to have a significant CP violating component. The measurement of its branching ratio could support the Standard Model or could indicate the existence of new physics. This letter reports new results from the 1999-2000 data set. One event is observed with an expected background at 0.99 +/- 0.35 events. We set a limit on the branching ratio of 3.5 x 10^(-10) at the 90% confidence level. Combining the results with the dataset taken in 1997 yields the final KTeV result: BR(KL --> pi0 ee) < 2.8 x 10^(-10) at 90% CL.Comment: 4 pages, three figure

Microgravity diode laser spectroscopy measurements in a reacting vortex ring

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76896/1/AIAA-2001-187-556.pd

Measurements of Direct CP Violation, CPT Symmetry, and Other Parameters in the Neutral Kaon System

We present a series of measurements based on K -> pi+pi- and K -> pi0pi0 decays collected in 1996-1997 by the KTeV experiment (E832) at Fermilab. We compare these four K -> pipi decay rates to measure the direct CP violation parameter Re(e'/e) = (20.7 +- 2.8) x 10^-4. We also test CPT symmetry by measuring the relative phase between the CP violating and CP conserving decay amplitudes for K->pi+pi- (phi+-) and for K -> pi0pi0 (phi00). We find the difference between the relative phases to be Delta-phi = phi00 - phi+- = (+0.39 +- 0.50) degrees and the deviation of phi+- from the superweak phase to be phi+- - phi_SW =(+0.61 +- 1.19) degrees; both results are consistent with CPT symmetry. In addition, we present new measurements of the KL-KS mass difference and KS lifetime: Delta-m = (5261 +- 15) x 10^6 hbar/s and tauS = (89.65 +- 0.07) x 10^-12 s.Comment: Submitted to Phys. Rev. D, August 6, 2002; 37 pages, 32 figure

VLA resolves unexpected radio structures in the Perseus Cluster of galaxies

High Energy Astrophysic

Measurements Of The Decay Kl → E+e-μ+μ-

Several 132 KL → e+e- μ+ μ- events were observed from the 1997 and 1999 runs of the KTeV experiments, with an estimated background of 0.8 events. In the first measurement of the parameter α using this decay mode, it was found that α=-1.59±0.37. No evidence was found for CP-violating contributions to the KLγ*γ* interaction.9014141801/1141801/5Wolfenstein, L., (1983) Phys. Rev. Lett., 51, p. 1945Belanger, G., Geng, C.Q., (1991) Phys. Rev. D, 43, p. 140Buras, A.J., Fleischer, R., (1998) Advanced Ser. Direct. High Energy Phys., 15, p. 65Uy, Z.E.S., (1991) Phys. Rev. D, 43, p. 802D'Ambrosio, G., Isidori, G., Portolès, J., (1998) Phys. Lett. B, 423, p. 385Alavi-Harati, A., (2001) Phys. Rev. Lett., 87, p. 71801. , KTeV CollaborationAlavi-Harati, A., (2001) Phys. Rev. Lett., 86, p. 5425. , KTeV CollaborationUy, Z.E.S., (2002) Eur. Phys. J. C, 23, p. 113Alavi-Harati, A., (2001) Phys. Rev. Lett., 87, p. 111802. , KTeV CollaborationHamm, J.C., (2002), Ph.D. thesis, The University of Arizona(Fermilab Report No. fERMILAB-THESIS-2002-09)Alavi-Harati, A., (1999) Phys. Rev. Lett., 83, p. 922. , KTeV CollaborationAlavi-Harati, A., (2000) Phys. Rev. D, 61, p. 072006. , KTeV CollaborationBrown, C., (1996) Nucl. Instrum. Methods Phys. Res., Sect. A, 369, p. 248Quinn, G.B., (2000), Ph.D. thesis, The University of ChicagoBarker, A.R., Huang, H., Toale, P.A., Engle, J., hep-ph/0210174Bergström, L., Massó, E., Singer, P., (1983) Phys. Lett., 131 B, p. 229Fanti, V., (1999) Phys. Lett. B, 458, p. 553. , NA48 Collaboratio