The only naturally occurring isotope of bismuth, super(209)Bi, is commonly regarded as the heaviest stable isotope. But like most other heavy nuclei abundant in nature and characterized by an ...exceptionally long lifetime, it is metastable with respect to alpha-decay. However, the decay usually evades observation because the nuclear structure of super(209)Bi gives rise to an extremely low decay probability and, moreover, generates low-energy alpha- particles difficult to detect. Indeed, dedicated experiments attempting to record the alpha-decay of super(209)Bi in nuclear emulsions failed. However, scintillating bolometers operated at temperatures below 100 mK offer improved detection efficiency and sensitivity, whereas a broad palette of targets could be available. Here we report the successful use of this method for the unambiguous detection of super(209)Bi alpha-decay in bismuth germanate detectors cooled to 20 mK. We measure an energy release of 3,137 +/- 1 (statistical) +/- 2 (systematic) keV and a half-life of (1.9 +/- 0.2) x 10 super(19) yr, which are in agreement with expected values.
Hydrogen ion titration curves of tobacco mosaic virus protein have been measured in various conditions of protein concentration, temperature, ionic strength, and rate of pH change. The polymers ...present at each stage are deduced from turbidity and sedimentation data, plus published information. A simple semi‐quantitative analysis of the curves is given, and the pK values of the two abnormal carboxylates in single helix are estimated as 6.4 and about 7.0. Disks, and some faster‐forming unknown polymers in the same size range, have one abnormal carboxylate with pK 6.9. These results are most easily interpreted in terms of electrostatic interactions between carboxylates, probably at the axial ends of the protein subunits.
TMV vulgare, A 14, Ni 725; Two-and Three-Layer Aggregates, Structural and Mechanistic Differences, Inter-Subunit Interactions, Non-Specific Aggregations The aggregation behaviour of tobacco mosaic ...virus (TMV) protein vulgare was compared to that of two mutants, A 14 and Ni725, with amino acid exchanges localized in the coat protein at posi tions 107 (Thr → Met, in N i725) and 129 (lie → Thr, in both mutants). This behaviour, as meas ured by sedimentation, hydrogen ion titration, light-scattering, and near-UV absorption difference and circular dichroism (CD) spectroscopy, differs characteristically both in the range of the A-protein (pH 8) and near neutrality, whereas nuclear magnetic resonance (NMR) and far-UV CD point at only subtle, or no structural differences between the three strains.
Near pH 8, the A-proteins of both mutants sediment nearly exclusively as 8 S aggregates, under conditions where vulgare protein forms a 4 S /8 S mixture (two-layer and three-layer aggregates, Vogel etal. in conditions where vulgare 4S aggregates dominate, both mutants sediment as a 4 S /8 S mixture. The average molecular weights of the 8S proteins corre spond to 12 (vulgare) to 15 (mutants) subunits. -Near neutrality both mutants titrate and polyme rize more cooperatively than vulgare protein; additionally, the pK(app.) of Ni 725 is shifted up wards, due to the higher a-helix forming potential of Met against Thr (pos. 107). Both mutants form large aggregates (> 200 S) of obviously helical conformation, by the uptake of one proton per subunit, whereas 20 S-disks constituting, under the same conditions, the stable entities in vul gare protein, are made only in minor amounts. These large mutant aggregates are remarkably more stable than the vulgare "overshoot" aggregates which transiently, too, may approach s-values and turbidities similar to the mutant aggregates; conformational changes, observed prior or in parallel to the formation of vulgare overshoot and disk aggregates, are significantly retarded in the large mutant aggregates. – Raising the ionic strength seems the only way to form mutant disks and stacks of disks (20-30 S) comparable to vulgare, pointing to the different pathways of disk formation, either at neutral pH or high ionic strength. – Evidence is given that the 8S aggregates of both mutant and vulgare proteins may behave similar in aggregation, the differences mainly being inserted by the 4S (two-layer) aggregates present in vulgare protein, which near neutrality seem responsible for the direct formation of (two-layer) disks. -The non-conservative exchange in po sition 129, altering the environment of Trp residues (52+17?), should weaken the "extended salt-bridge system" ("pairing") observed between the two layers of the disk (Bloomer et al., Nature, 1978). A competition is suggested between the strength of this pairing, and the binding of a third layer, regulating the mode of aggregation to two-layer, to three-layer, and to higher aggregates; this is corroborated by comparison with published results on temperature-sensitive (ts I) mutants and chemically modified proteins. – To explain the effects of residue 129 on the titration of the protein we suggest a mechanical analogy, made up of a balance between the charge and state of the "carboxyle cage" (Stubbs et al., Nature, 1977), as regulatory site, and the strength of the
Metastable ‘overshoot’ aggregates are formed when tobacco mosaic virus A‐protein (4–8 S) polymerises to disks (20–22 S) and stacks of disks (27–30 S) at pH 6.8–7.6, 20–25 °C. Two cases are ...discernible. First, at ionic strength 0.1 M, below pH 7.1, a transient, definite 26‐S peak appears: it transforms in a matter of hours into stable 22‐S (disk) aggregates, at a rate that decreases with decreasing pH and increasing temperature; above pH 7.1, there are only 4–8‐S and 22‐S aggregates. Second, after a rapid increase of ionic strength from 0.1 to 0.75 M, below pH 7.6 a broad distribution of very large overshoot aggregates forms (maximum at 60 S, at pH 6.9). With decreasing pH, the maximum size of the overshoot aggregates increases and reequilibration to stacks of two disks (28 S) becomes slower. The 4–8‐S and 26‐S aggregates can both form the very large overshoot aggregates, but disks and stacks of disks alone cannot.
Under these conditions, disks undergo only limited stacking (27–30 S) and a very slow conformational change. A similar conformational change parallels the decomposition of the very large overshoot aggregates. At pH 8, overshoot does not occur, probably because a higher pH inhibits the growth of rods.
Though the structure of the overshoot‐forming aggregates is still unknown, three‐layer aggregates (8 S and 26 S) are one possibility. We present a scheme including all reversible polymerisations so far observed for TMV protein and discuss their implications for the reconstitution of the virus in vitro.
Astrophys.J.654:825-834,2007 We have observed the cluster RX J0152.7-1357 (z$\sim$0.83) at 24$\mu$m with
the Multiband Imaging Photometer for Spitzer (MIPS). We detected twenty-two
sources associated ...with spectroscopically confirmed cluster members, while ten
more have photometric redshifts compatible with membership. Two of the 32
likely cluster members contain obvious active nuclei while the others are
associated with dusty star formation. The median IR-determined star formation
rate among the remaining galaxies is estimated at 22 M$_\odot$$ $yr$^{-1}$,
significantly higher than in previous estimates from optical data. Most of the
MIR-emitting galaxies also have optical emission lines, but a few do not and
hence have completely hidden bursts of star formation or AGN activity.
An excess of MIR-emitting galaxies is seen in the cluster in comparison to
the field at the same redshift. The MIR cluster members are more associated
with previously detected infalling late type galaxies rather than triggered by
the ongoing merging of bigger X-ray clumps. Rough estimates also show that ram
pressure may not be capable of stripping the gas away from cluster outskirt
galaxies but it may disturb the gas enough to trigger the star formation
activity. Harassment can also play a role if for example these galaxies belong
to poor galaxy groups. Thus, bursts of star formation occur in the cluster
environment and could also help consume the galaxy gas content in addition to
ram pressure, harassment or galaxy-galaxy strong interactions.
Photometric data of galaxies covering the rest-frame wavelength range from far-UV to far-IR make it possible to derive galaxy properties with a high reliability by fitting the attenuated stellar ...emission and the related dust emission at the same time. For this purpose we wrote the code CIGALE (Code Investigating GALaxy Emission) that uses model spectra composed of the Maraston (or PEGASE) stellar population models, synthetic attenuation functions based on a modified Calzetti law, spectral line templates, the Dale & Helou dust emission models, and optional spectral templates of obscured AGN. Depending on the input redshifts, filter fluxes are computed for the model set and compared to the galaxy photometry by carrying out a Bayesian-like analysis. CIGALE was tested by analysing 39 nearby galaxies selected from SINGS. The reliability of the different model parameters was evaluated by studying the resulting expectation values and their standard deviations in relation to the input model grid. Moreover, the influence of the filter set and the quality of photometric data on the code results was estimated. For up to 17 filters between 0.15 and 160 mum, we find robust results for the mass, star formation rate, effective age of the stellar population at 4000 A, bolometric luminosity, luminosity absorbed by dust, and attenuation in the far-UV. A study of the mutual relations between the reliable properties confirms the dependence of star formation activity on morphology in the local Universe and indicates a significant drop in this activity at about 10^11 M_sol towards higher total stellar masses. The dustiest sample galaxies are present in the same mass range. abridged
We present ISOCAM 15 micron and MIPS 24 micron photometry of a sample of 16
distant Luminous Infrared Galaxies (LIRGs) characterized by a median luminosity
L(IR) 2x10^11 Lsol and redshift z = 0.7 ...(distributed from z = 0.1 to 1.2).
While some sources display 24/15 micron flux ratios also consistent with a
featureless continuum dominating their mid-infrared (MIR) spectral energy
distributions (SEDs), the presence of prominent emission features such as the
Polycyclic Aromatic Hydrocarbons is clearly required to explain the observed
colors for more than half of the sample. As a result, a general good agreement
is observed between the data and predictions from the local starburst-dominated
SEDs that have been used so far to constrain IR galaxy evolution. This is
consistent with the star-forming nature of LIRGs derived from previous works,
even though our approach cannot rule out the dominance of an AGN in some cases.
Our study also supports the possibility of tracing the total IR luminosity of
distant galaxies (up to z ~ 1) from their MIR emission.
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