Trailing Edge Unification via an Intermediate Pati-Salam Group

We demonstrate to two-loop order that an intermediate symmetrically embedded Pati-Salam $SU(2)_L \times SU(2)_R \times SU(4)$ level of symmetry is all that is necessary to accommodate empirical values of $\alpha(M_z), \alpha_s(M_z)$ and $\sin^2\theta_w(M_z)$ within a grand unification context but with a high (10^{14} GeV) intermediate mass scale and with a concomitant higher GUT scale.Comment: 7 pages, 4 embedded eps figur

Canavanine Inhibits Vimentin Assembly But Not Its Synthesis in Chicken Embryo Erythroid Cells

In chicken embryo erythroid cells, newly synthesized vimentin first enters a Triton X-100 (TX-100)-soluble pool and subsequently assembles posttranslationally into TX-100-insoluble vimentin filaments (Blikstad I., and E. Lazarides, J. Cell Biol., 96:1803-1808). Here we show that incubation of chicken embryo erythroid cells in a medium in which arginine has been substituted by its amino acid analogue, canavanine, results in the inhibition of the posttranslational assembly of vimentin into the TX-100-insoluble filaments. Immunoprecipitation and subsequent SDS gel electrophoresis showed that the synthesis of canavanine-vimentin is not inhibited and that it accumulates in the TX-100-soluble compartment. Pulse-chase experiments with [35S]methionine demonstrated that while arginine-vimentin can be rapidly chased from the soluble to the cytoskeletal fraction, canavanine-vimentin remains in the soluble fraction, where it turns over. The effect of canavanine on the assembly of vimentin did not prevent the assembly of arginine-vimentin, as cells labeled with [35S]methionine first in the presence of canavanine and then in the presence of arginine contained labeled canavanine-vimentin only in the soluble fraction, and arginine-vimentin in both the soluble and cytoskeletal fractions. These results suggest that arginine residues play an essential role in the assembly of vimentin in vivo

Biogenesis of the Avian Erythroid Membrane Skeleton : Receptor-mediated Assembly and Stabilization of Ankyrin (Goblin) and Spectrin

Ankyrin is an extrinsic membrane protein in human erythrocytes that links the αß-spectrin-based extrinsic membrane skeleton to the membrane by binding simultaneously to the ß-spectrin subunit and to the transmembrane anion transporter. To analyse the temporal and spatial regulation of assembly of this membrane skeleton, we investigated the kinetics of synthesis and assembly of ankyrin (goblin) with respect to those of spectrin in chicken embryo erythroid cells. Electrophoretic analysis of Triton X-100 soluble and cytoskeletal fractions show that at steady state both ankyrin and spectrin are detected exclusively in the cytoskeleton . In contrast, continuous labeling of erythroid cells with [(^35)S]methionine, and immunoprecipitation of ankyrin and α- and ß- spectrin, reveals that newly synthesized ankyrin and spectrin are partitioned into both the cytoskeletal and Triton X-100 soluble fractions . The soluble pools of ankyrin and ß-spectrin reach a plateau of labeling within 1 h, whereas the soluble pool of α-spectrin is substantially larger and reaches a plateau more slowly, reflecting an approximately 3:1 ratio of synthesis of α- to ß-spectrin. Ankyrin and ß-spectrin enter the cytoskeletal fraction within 10 min of labeling, and the amount assembled into the cytoskeletal fraction exceeds the amount present in their respective soluble pools within 1 h of labeling. Although α-spectrin enters the cytoskeletal fraction with similar kinetics to ß-spectrin and ankyrin, and in amounts equimolar to ß-spectrin, the amount of cytoskeletal α-spectrin does not exceed the amount of soluble α-spectrin even after 3 h of labeling. Pulse-chase labeling experiments reveal that ankyrin and α- and ß-spectrin assembled into the cytoskeleton exhibit no detectable turnover, whereas the Triton X-100 soluble polypeptides are rapidly catabolized, suggesting that stable assembly of the three polypeptides is dependent upon their association with their respective membrane receptor(s). The existence in the detergent-soluble compartment of newly synthesized ankyrin and α- and ß-spectrin that are catabolized, rather than assembled, suggests that ankyrin and spectrin are synthesized in excess of available respective membrane binding sites, and that the assembly of these polypeptides, while rapid, is not tightly coupled to their synthesis. We hypothesize that the availability of the high affinity receptor(s) localized on the membrane mediates posttranslationally the extent of assembly of the three cytoskeletal proteins in the correct stoichiometry, their stability, and their spatial localization

Liquid-Metal-Enabled Synthesis of Aluminum-Containing III-Nitrides by Plasma-Assisted Molecular Beam Epitaxy

Nitride films are promising for advanced optoelectronic and electronic device applications. However, some challenges continue to impede development of high aluminum-containing devices. The two major difficulties are growth of high crystalline quality films with aluminum-rich compositions, and efficiently doping such films p-type. These problems have severely limited use of aluminum-rich nitride films grown by molecular beam epitaxy. A way around these problems is through use of a liquid-metal-enabled approach to molecular beam epitaxy. Although the presence of a liquid metal layer at the growth front is reminiscent of conventional liquid phase epitaxy, this approach is different in its details. Conventional liquid epitaxy is a near-thermodynamic equilibrium process which liquid-metal assisted molecular beam epitaxy is not. Growth of aluminum-rich nitrides is primarily driven by the kinetics of the molecular vapor fluxes, and the surface diffusion of adatoms through a liquid metal layer before incorporation. This paper reports on growth of high crystalline quality and highly doped aluminum-containing nitride films. Measured optical and electrical characterization data show that the approach is viable for growth of atomically smooth aluminum-containing nitride heterostructures. Extremely high p-type doping of up to $6 \times 10$$^{17}$ cm$^{-3}$ and n-type doping of up to $1 \times 10$$^{20}$ cm$^{-3}$ in Al$_{0.7}$Ga$_{0.3}$N films was achieved. Use of these metal-rich conditions is expected to have a significant impact on high efficiency and high power optoelectronic and electronic devices that require both high crystalline quality and highly doped (Al,Ga)N films

C*-algebras and Equivalences for C*-correspondences

We study several notions of shift equivalence for C*-correspondences and the effect that these equivalences have on the corresponding Pimsner dilations. Among others, we prove that non-degenerate, regular, full C*-correspondences which are shift equivalent have strong Morita equivalent Pimsner dilations. We also establish that the converse may not be true. These results settle open problems in the literature. In the context of C*-algebras, we prove that if two non-degenerate, regular, full C*-correspondences are shift equivalent, then their corresponding Cuntz-Pimsner algebras are strong Morita equivalent. This generalizes results of Cuntz and Krieger and Muhly, Tomforde and Pask. As a consequence, if two subshifts of finite type are eventually conjugate, then their Cuntz-Krieger algebras are strong Morita equivalent. Our results suggest a natural analogue of the Shift Equivalence Problem in the context of C*-correspondences. Even though we do not resolve the general Shift Equivalence Problem, we obtain a positive answer for the class of imprimitivity bimodules.Comment: 30 pages; Results on the minimality of the Pimsner dilation added in Section