Active Asteroids

Abstract. Asteroids and comets have been thought to be two separate kinds of objects in our solar system. In recent years, however, evidence has been found that there is a continuum of objects that have both asteroid-like and comet-like properties. Active asteroids are objects with typical asteroid orbits that eject dust almost like comets, forming dust tails. They can lose mass by different mechanisms, which include ice sublimation, impact ejection, rotational instability, electrostatic forces, thermal stresses, dehydration, sodium volatilization, and radiation pressure. There are some challenges in observing asteroid activity, but two dozen mass-losing asteroids have been found. Examples of active asteroids are the main-belt comet 133P/(7968) Elst-Pizarro where ice sublimates, the large main-belt asteroid (596) Scheila that collided with a smaller body, and the near-Earth asteroid (3200) Phaethon whose mass-loss is likely related to thermal stresses and sodium volatilization. In the future, more research is needed in active asteroid observations, models, and laboratory experiments. Space missions with active asteroids as their targets have also been planned

Construction of a flocculent Saccharomyces cerevisiae strain secreting high levels of Aspergillus niger β-galactosidase

A flocculent Saccharomyces cerevisiae strain secreting Aspergillus niger β-galactosidase activity was constructed by transforming S. cerevisiae NCYC869-A3 strain with plasmid pVK1.1 harboring the A. niger β-galactosidase gene, lacA, under the control of the ADH1 promoter and terminator. Compared to other recombinant S. cerevisiae strains, this recombinant yeast has higher levels of extracellular β-galactosidase activity. In shakeflask cultures, the β-galactosidase activity detected in the supernatant was 20 times higher than that obtained with previously constructed strains (Domingues et al. 2000a). In bioreactor culture, with cheese-whey permeate as substrate, a yield of 878.0 nkat/gsubstrate was obtained. The recombinant strain is an attractive alternative to other fungal β-galactosidase production systems as the enzyme is produced in a rather pure form. Moreover, the use of flocculating yeast cells allows for enzyme production with high productivity in continuous fermentation systems with facilitated downstream processing.Instituto de Biotecnologia e Química Fina (IBQF).Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BD/11306/97

Q_EC values of the Superallowed beta-Emitters 10-C, 34-Ar, 38-Ca and 46-V

The Q_EC values of the superallowed beta+ emitters 10-C, 34-Ar, 38-Ca and 46-V have been measured with a Penning-trap mass spectrometer to be 3648.12(8), 6061.83(8), 6612.12(7) and 7052.44(10) keV, respectively. All four values are substantially improved in precision over previous results.Comment: 9 pages, 7 figures, 5 table

Isomeric states close to doubly magic 132^{132}Sn studied with JYFLTRAP

The double Penning trap mass spectrometer JYFLTRAP has been employed to measure masses and excitation energies for $11/2^-$ isomers in $^{121}$Cd, $^{123}$Cd, $^{125}$Cd and $^{133}$Te, for $1/2^-$ isomers in $^{129}$In and $^{131}$In, and for $7^-$ isomers in $^{130}$Sn and $^{134}$Sb. These first direct mass measurements of the Cd and In isomers reveal deviations to the excitation energies based on results from beta-decay experiments and yield new information on neutron- and proton-hole states close to $^{132}$Sn. A new excitation energy of 144(4) keV has been determined for $^{123}$Cd$^m$. A good agreement with the precisely known excitation energies of $^{121}$Cd$^m$, $^{130}$Sn$^m$, and $^{134}$Sb$^m$ has been found.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Nanoelectronic thermometers optimised for sub-10 millikelvin operation

We report the cooling of electrons in nanoelectronic Coulomb blockade thermometers below 4 mK. Above 7 mK the devices are in good thermal contact with the environment, well isolated from electrical noise, and not susceptible to self-heating. This is attributed to an optimised design that incorporates cooling fins with a high electron-phonon coupling and on-chip electronic filters, combined with a low-noise electronic measurement setup. Below 7 mK the electron temperature is seen to diverge from the ambient temperature. By immersing a Coulomb Blockade Thermometer in the 3He/4He refrigerant of a dilution refrigerator, we measure a lowest electron temperature of 3.7 mK.Comment: 11 pages, 4 figures. (Fixed fitted saturation T_e on p9

Multiwalled carbon nanotube: Luttinger liquid or not?

We have measured IV-curves of multiwalled carbon nanotubes using end contacts. At low voltages, the tunneling conductance obeys non-Ohmic power law, which is predicted both by the Luttinger liquid and the environment-quantum-fluctuation theories. However, at higher voltages we observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees with the environment-quantum-fluctuation theory, but cannot be explained by the Luttinger-liquid theory. From the high-voltage tunneling conductance we determine the transmission line parameters of the nanotubes.Comment: RevTeX, 4 pages, 2 EPS-figures, submitted to Phys. Rev. Let

Construction of a flocculent brewer’s yeast strain producing an Aspergillus niger β-galactosidase

Praxis XXI (BD/11306/97).European Science Foundation (ESF).Center for International Mobility (CIMO)

Construction of a flocculent brewer's yeast strain secreting Aspergillus niger β-galactosidase

One way of improving heterologous protein production is to use high cell density systems, one of the most attractive being the flocculating yeast production system. Also, lactose is available in large amounts as a waste product from cheese production processes. The construction of flocculent and non-flocculent brewer's yeast strains secreting β-galactosidase and growing on lactose is presented. A plasmid was constructed coding for an extracellular β-galactosidase of Aspergillus niger and having, as selective marker, the yeast CUP1 gene conferring resistance to copper. This selective marker allows for the transformation of wild-type yeasts. This work represents an important step towards the study of heterologous protein secretion by flocculent cells.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BD/11306/97.Finland. Center For International Mobility.European Science Foundation