Magnetic flux locking in two weakly coupled superconducting rings

We have analyzed the quantum interference effects in the macroscopic ''superconducting molecule''. The composite system consists of two massive superconducting rings, each interrupted by a Josephson junction, which are at the same time weakly coupled with one another. The special case of coupling via the Josephson four-terminal junction is considered. The structure of the macroscopic quantum states in an applied magnetic field is calculated. It is shown, that depending on the values of the magnetic fluxes through each ring, the system displays two groups of states, the ''orthostates'' with both induced currents going in the same direction, and the ''parastates'' with the opposite currents and with the total induced flux locked to zero value. The transition to the flux locked state with changing of the total applied flux is sudden and is preserved in a certain interval which is determined by the difference of the fluxes applied through each ring. It makes the system sensitive to small gradients of the external magnetic field.Comment: 8 pages in Latex, 3 figures (eps

Micro & strong lensing with the Square Kilometer Array: The mass--function of compact objects in high--redshift galaxies

We present the results from recent VLA 8.5-GHz and WSRT 1.4 and 4.9-GHz monitoring campaigns of the CLASS gravitational lens B1600+434 and show how the observed variations argue strongly in favor of microlensing by MACHOs in the halo of a dark-matter dominated edge-on disk galaxy at z=0.4. The population of flat-spectrum radio sources with micro-Jy flux-densities detected with the Square-Kilometer-Array is expected to have dimensions of micro-arcsec. They will therefore vary rapidly as a result of Galactic scintillation (diffractive and refractive). However, when positioned behind distant galaxies they will also show variations due to microlensing, even more strongly than in the case of B1600+434. Relativistic or superluminal motion in these background sources typically leads to temporal variations on time scales of days to weeks. Scintillation and microlensing can be distinguished, and separated, by their different characteristic time scales and the frequency dependence of their modulations. Monitoring studies with Square-Kilometer-Array at GHz frequencies will thus probe both microscopic and macroscopic properties of dark matter and its mass-function as a function of redshift, information very hard to obtain by any other method.Comment: 8 pages, 5 figures, to appear in Perspectives in Radio Astronomy: Scientific Imperatives at cm and m Wavelengths (Dwingeloo: NFRA), Edited by: M.P. van Haarlem & J.M. van der Huls

A time-delay determination from VLA light curves of the CLASS gravitational lens B1600+434

We present Very Large Array (VLA) 8.5-GHz light curves of the two lens images of the Cosmic Lens All Sky Survey (CLASS) gravitational lens B1600+434. We find a nearly linear decrease of 18-19% in the flux densities of both lens images over a period of eight months (February-October) in 1998. Additionally, the brightest image A shows modulations up to 11% peak-to-peak on scales of days to weeks over a large part of the observing period. Image B varies significantly less on this time scale. We conclude that most of the short-term variability in image A is not intrinsic source variability, but is most likely caused by microlensing in the lens galaxy. The alternative, scintillation by the ionized Galactic ISM, is shown to be implausible based on its strong opposite frequency dependent behavior compared with results from multi-frequency WSRT monitoring observations (Koopmans & de Bruyn 1999). From these VLA light curves we determine a median time delay between the lens images of 47^{+5}_{-6} d (68%) or 47^{+12}_{-9} d (95%). We use two different methods to derive the time delay; both give the same result within the errors. We estimate an additional systematic error between -8 and +7 d. If the mass distribution of lens galaxy can be described by an isothermal model (Koopmans, de Bruyn & Jackson 1998), this time delay would give a value for the Hubble parameter, H_0=57^{+14}_{-11} (95% statistical) ^{+26}_{-15} (systematic) km/s/Mpc (Omega_m=1 and Omega_Lambda=0). Similarly, the Modified-Hubble-Profile mass model would give H_0=74^{+18}_{-15} (95% statistical) ^{+22}_{-22} (systematic) km/s/Mpc. For Omega_m=0.3 and Omega_Lambda=0.7, these values increase by 5.4%. ... (ABRIDGED)Comment: 14 pages, 6 figures, accepted for publication in Astronomy & Astrophysics (Figs 1 and 3 with degraded resolution

On the order of a non-abelian representation group of a slim dense near hexagon

We show that, if the representation group $R$ of a slim dense near hexagon $S$ is non-abelian, then $R$ is of exponent 4 and $|R|=2^{\beta}$, $1+NPdim(S)\leq \beta\leq 1+dimV(S)$, where $NPdim(S)$ is the near polygon embedding dimension of $S$ and $dimV(S)$ is the dimension of the universal representation module $V(S)$ of $S$. Further, if $\beta =1+NPdim(S)$, then $R$ is an extraspecial 2-group (Theorem 1.6)

A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater

A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 220 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys

The role of acquaintanceship in the perception of child behaviour problems

The role of acquaintanceship with the child on reports of child behaviour by different informants was examined within the framework of a general theory of personality judgment. Mothers of referred children and group-care workers rated videotaped behaviour samples of a well known and an unknown child in the clinic. Independent observers also rated the videotapes. In line with the acquaintanceship hypothesis, mothers were found to perceive more behaviour problems than independent observers when rating well known children but not unknown children. Contrary to the acquaintanceship hypothesis, however, the group-care workers in our study reported more behaviour problems than the other informants regardless of their acquaintance with the children. The clinical and methodological implications of these findings are discussed

The Aqueous Phase Yield Of Alkyl Nitrates From Roo+No: Implications For Photochemical Production In Seawater

Alkyl nitrates have been observed in remote oceanic regions of the troposphere and in the surface ocean. The mechanism for their production in the oceans is not known. A likely source is the reaction of ROO + NO (where R is an alkyl group). Steady-state laboratory experiments show that alkyl nitrates are produced in the aqueous phase via this reaction, with branching ratios of 0.23 +/- 0.04, 0.67 +/- 0.03, and 0.71 +/- 0.04 for methyl, ethyl, and propyl nitrate respectively. The branching ratios in aqueous solution are significantly higher than in the gas phase. Irradiation of surface seawaters yield rates of alkyl nitrate production on the order of 10(-18) mol cm(-3) s(-1), suggesting that the reaction of ROO and NO is an important source of alkyl nitrates in seawater