Bacterial Diversity in the Uranium Mill-Tailing Gittersee as Estimated via a 16S rDNA Approach

Bacterial diversity in a soil sample collected from uranium mill-tailings called Gittersee and situated near the city of Dresden, Germany, was analysed by using a culture-independent 16S rDNA approach exploiting PCR ampli�cation primers 7F and 1513R. The results were compared with those obtained earlier analysing the same sample by using another primer pair, namely 43F-1404R [1]. The two 16S rDNA approaches demonstrated that Proteobacteria were the most predominant group in the sample, followed by Cytophaga/Flavobacterium/Bacteroides and by Gram positive bacteria with low and with high G+C content, too. A large number of 16S rDNA sequences from two libraries were identical or almost identical. However, the ratio between the bacterial groups represented in them signifcantly differed. 7F-1513R primer set retrieved in addition to the above mentioned sequences also 16S rRNA genes, those of green non-sulphur bacteria and representatives of AD1 and OP11 divisions. The latter indicates that 7F-1513R primer set seems to be more reliable in analyses of bacterial diversity

Nonequilibrium Relaxations and Aging Effects in a Two-Dimensional Coulomb Glass

The relaxations of conductivity have been studied in the glassy regime of a strongly disordered two-dimensional electron system in Si after a temporary change of carrier density during the waiting time t_w. Two types of response have been observed: a) monotonic, where relaxations exhibit aging, i.e. dependence on history, determined by t_w and temperature; b) nonmonotonic, where a memory of the sample history is lost. The conditions that separate the two regimes have been also determined.Comment: 4 pages; published versioi

Observation of Mass Transport through Solid 4He

By use of a novel experimental design, one that provides for superfluid helium in contact with bulk hcp 4He off the melting curve, we have observed the DC transport of mass through a cell filled with solid 4He in the hcp region of the phase diagram. Flow, which shows characteristics of a superflow, is seen to be independent of the method used to grow the solid, but depends on pressure and temperature. The temperature dependence suggests the possibility of hysteresis.Comment: 1 zipped file, produces 16 page paper, with 20 figures; resubmitted with typos corrected, a figure corrected, some discussion improved, and additional references - still 16 pages and 20 figure

Radio-Frequency Single-Electron Refrigerator

We propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunnelling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of $\sim k_{\rm B}T \times f$ at temperature $T$ over a wide range of cycle frequencies $f$. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of $\sim k_{\rm B}T/\Delta$, where $\Delta$ is the superconducting gap. The performance is not affected significantly by non-idealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.Comment: 5 pages, 4 figures; corrected typos, language improve

Adiabatic Magnetization of Superconductors as a High-Performance Cooling Mechanism

The adiabatic magnetization of a superconductor is a cooling principle proposed in the 30s, which has never been exploited up to now. Here we present a detailed dynamic description of the effect, computing the achievable final temperatures as well as the process timescales for different superconductors in various regimes. We show that, although in the experimental conditions explored so far the method is in fact inefficient, a suitable choice of initial temperatures and metals can lead to unexpectedly large cooling effect, even in the presence of dissipative phenomena. Our results suggest that this principle can be re-envisaged today as a performing refrigeration method to access the microK regime in nanodevices.Comment: 4 pages, 3 color figure

Phenol Biodegradation by Two Xenobiotics-Tolerant Bacteria Immobilized in Polyethylene Oxide Cryogels

Biofilms were formed on poly(ethylene oxide) (PEO) cryogels by using bacteria cultured from xenobiotics polluted environments and their phenol biodegrading capability was studied. PEO cryogels were synthesized via UV irradiation cross linking of moderately frozen aqueous system. Two xenobiotics tolerant bacterial isolates KCM R5 and KCM RG5 were used to construct the biofilms on the cryogels. Obtained PEO-biofilms were assessed for their ability to remove phenol at concentrations 300, 400, 600 and 1000 mg L-1 for 28 days. The biofilm PEO-KCM RG5 removed phenol up to 600mg L-1/24 h, whereas the biofilm PEO-KCM R5 was able to degrade up to 1000 mg L-1/24 h. The high content of free-water in the cryogels allowed reproduction of the used bacteria. The high content of free-water in the cryogels allowed reproduction of the used bacteria. Short initial adaptation of the PEO-bio�lms with 100 mg L-1/24 h phenol was crucial for protecting the bacterial cells from dead. The obtained results showed that the liquid debit through the bio�lms on the 28th day of the experiments was lower than at the beginning. The cryogels demonstrated non-toxicity, high biocompatibility with bacteria and excellent mechanical characteristics. After aggressive phenol treatment the PEO-biofilms remained compact, porous and elastic. The investigated new biological materials demonstrate potential for application in the industrial wastewater treatment technologies

Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7

The magnetocaloric effect of polycrystalline samples of pure and Y-doped dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic interest, it is proposed that the magnetocaloric effect may be used as an appropriate tool for the qualitative study of slow relaxation processes in the spin ice regime. In the high temperature regime the temperature change on adiabatic demagnetization was found to be consistent with previously published entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by adiabatic demagnetization was followed by an irreversible rise in temperature that persisted after the removal of the applied field. The relaxation time derived from this temperature rise was found to increase rapidly down to 0.3 K. The data near to 0.3 K indicated a transition into a metastable state with much slower relaxation, supporting recent neutron scattering results. In addition, magnetic dilution of 50 % concentration was found to significantly prolong the dynamical response in the milikelvin temperature range, in contrast with results reported for higher temperatures at which the spin correlations are suppressed. These observations are discussed in terms of defects and loop correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.