Protein Mobility in the Cytoplasm of Escherichia coli

The rate of protein diffusion in bacterial cytoplasm may constrain a variety of cellular functions and limit the rates of many biochemical reactions in vivo. In this paper, we report noninvasive measurements of the apparent diffusion coefficient of green fluorescent protein (GFP) in the cytoplasm of Escherichia coli. These measurements were made in two ways: by photobleaching of GFP fluorescence and by photoactivation of a red-emitting fluorescent state of GFP (M. B. Elowitz, M. G. Surette, P. E. Wolf, J. Stock, and S. Leibler, Curr. Biol. 7:809-812, 1997). The apparent diffusion coefficient, Da, of GFP in E. coli DH5alpha was found to be 7.7 ± 2.5 µm^2/s. A 72-kDa fusion protein composed of GFP and a cytoplasmically localized maltose binding protein domain moves more slowly, with Da of 2.5 ± 0.6 µm^2/s. In addition, GFP mobility can depend strongly on at least two factors: first, Da is reduced to 3.6 ± 0.7 µm^2/s at high levels of GFP expression; second, the addition to GFP of a small tag consisting of six histidine residues reduces Da to 4.0 ± 2.0 µm^2/s. Thus, a single effective cytoplasmic viscosity cannot explain all values of Da reported here. These measurements have implications for the understanding of intracellular biochemical networks

Expected Precision of Higgs Boson Partial Widths within the Standard Model

We discuss the sources of uncertainty in calculations of the partial widths of the Higgs boson within the Standard Model. The uncertainties come from two sources: the truncation of perturbation theory and the uncertainties in input parameters. We review the current status of perturbative calculations and note that these are already reaching the parts-per-mil level of accuracy for the major decay modes. The main sources of uncertainty will then come from the parametric dependences on alpha_s, m_b, and m_c. Knowledge of these parameters is systematically improvable through lattice gauge theory calculations. We estimate the precision that lattice QCD will achieve in the next decade and the corresponding precision of the Standard Model predictions for Higgs boson partial widths.Comment: 20 pages, 1 figure; v2: minor typo correction

Effects of breed type, silage harvest date and pattern of offering concentrates on intake, performance and carcass traits of finishing steers

peer-reviewedThe objective of this experiment was to investigate the effects and interactions of breed type, silage harvest date and pattern of offering concentrates on intake, performance and carcass traits of finishing steers. Seventy-two steers (36 Friesian and 36 beef cross) were blocked on weight within breed type and assigned to a pre-experimental slaughter group or to one of 4 dietary treatments in a 2 (breed type) 2 (early- or late- cut silage) 2 (flat rate or varied pattern of offering concentrates) factorial arrangement of treatments. The flat-rate feeding pattern was silage ad libitum plus 5 kg concentrates per head daily to slaughter. The varied feeding pattern was silage only for 79 days followed by concentrates ad libitum to slaughter. All animals were slaughtered together after 164 days when the groups on the two feeding patterns had consumed the same total quantity of concentrates. Friesians had a higher (P < 0.001) silage dry matter (DM) intake and a higher (P < 0.01) total DM intake than the beef crosses. Live-weight gain was similar for both breed types but the beef-cross animals had a higher (P < 0.001) kill-out proportion, higher (P < 0.01) carcass gain, and better (P < 0.001) carcass conformation than the Friesians. The beef-cross type also had a higher (P < 0.001) proportion of muscle and a lower (P < 0.001) proportion of bone in the carcass. Silage harvest date had no effect on silage or total DM intakes but the early-cut silage did result in higher (P < 0.01) carcass gain. Animals on the varied feeding pattern consumed less (P < 0.01) silage DM and less (P < 0.001) total DM than those on the flat rate feeding pattern. Live-weight gain and carcass gain were similar for the two feeding patterns. It is concluded that Friesians had a higher intake, but had lower carcass gain than the beef-cross type. Animals on the early-cut silage had higher carcass gain than those on the late-cut silage. The varied feeding pattern resulted in lower DM intake but efficiency of feed energy utilisation was similar for both feeding patterns. Interactions were generally not statistically significant

Quantum phase transitions with Photons and Polaritons

We show that a system of polaritons - combined atom and photon excitations - in an array of coupled cavities, under an experimental set-up usually considered in electromagnetically induced transparency, is described by the Bose-Hubbard model. This opens up the possibility of using this system as a quantum simulator, allowing for the observation of quantum phase transitions and for the measurement of local properties, such as single site observables. All the basic building blocks of the proposed setting have already been achieved experimentally, showing the feasibility of its realization in the near future.Comment: 7 pages, contribution for the proceedings of the QCMC0

Feed intake pattern, behaviour, rumen characteristics and blood metabolites of finishing beef steers offered total mixed rations constituted at feeding or ensiling

peer-reviewedTwo experiments were undertaken. In Experiment 1, behaviour, intake pattern and blood metabolites, were recorded for steers offered total mixed rations (TMR) based on grass silage and concentrates, and constituted either at ensiling (E-TMR) or feedout (F-TMR). Fourteen continental crossbred steers (mean starting weight 505 (s.d. 41.5) kg) were assigned to each of the following eight treatments: grass silage offered ad libitum (SO), E-TMR diets constituted in approximate dry matter (DM) ratios of grass:concentrates of 75:25 (EL), 50:50 (EM) and 25:75 (EH), F-TMR diets constituted in approximate DM ratios of grass silage:concentrates of 75:25 (FL), 50:50 (FM) and 25:75 (FH), and finally concentrates ad libitum (AL). Total DM intake increased linearly (P < 0.001) and the time spent eating and ruminating decreased linearly (P < 0.001) with increasing concentrate proportion. Animals on the F-TMR diets had higher total DM intakes (P < 0.05) and plasma glucose (P < 0.05) and urea (P < 0.001) concentrations than animals on the corresponding E-TMR diets. No effect of method of feed preparation on intake pattern or behaviour was recorded. In Experiment 2, four ruminally cannulated Holstein-Friesian steers of mean initial live weight 630 (s.d. 23.2) kg were used to evaluate rumen characteristics for four of the above diets (FL, EL, FH and EH) in a 4 × 4 latin square design. Higher concentrate diets resulted in lower rumen pH (P < 0.05), higher lactic acid (P < 0.001) and ammonia (P < 0.05) concentrations and lower acetate:propionate (P < 0.05). F-TMR was associated with a higher (P < 0.05) rumen volatile fatty acid concentration but no difference in other rumen fermentation characteristics compared to E-TMR. Concentrate proportion and method of feed preparation had no effect (P > 0.05) on rumen pool sizes but animals consuming the high concentrate diet had a faster (P < 0.05) rumen passage rate of NDF than animals on the low concentrate diet.B. Cummins was in receipt of a Teagasc Walsh Fellowship

Eisenstein series for higher-rank groups and string theory amplitudes

Scattering amplitudes of superstring theory are strongly constrained by the requirement that they be invariant under dualities generated by discrete subgroups, E_n(Z), of simply-laced Lie groups in the E_n series (n<= 8). In particular, expanding the four-supergraviton amplitude at low energy gives a series of higher derivative corrections to Einstein's theory, with coefficients that are automorphic functions with a rich dependence on the moduli. Boundary conditions supplied by string and supergravity perturbation theory, together with a chain of relations between successive groups in the E_n series, constrain the constant terms of these coefficients in three distinct parabolic subgroups. Using this information we are able to determine the expressions for the first two higher derivative interactions (which are BPS-protected) in terms of specific Eisenstein series. Further, we determine key features of the coefficient of the third term in the low energy expansion of the four-supergraviton amplitude (which is also BPS-protected) in the E_8 case. This is an automorphic function that satisfies an inhomogeneous Laplace equation and has constant terms in certain parabolic subgroups that contain information about all the preceding terms.Comment: Latex. 38 pages. 1 figure. v2: minor changes and clarifications. v3: minor corrections, version to appear in Communications in Number Theory and Physics. v4: corrections to table