Polarization singularities in the clear sky

Ideas from singularity theory provide a simple account of the pattern of polarization directions in daylight. The singularities (two near the Sun and two near the anti-Sun) are points in the sky where the polarization line pattern has index +1/2 and the intensity of polarization is zero. The singularities are caused by multiple scattering that splits into two each of the unstable index +1 singularities at the Sun and anti-Sun, which occur in the single-dipole scattering (Rayleigh) theory. The polarization lines are contours of an elliptic integral. For the intensity of polarization (unnormalized degree), it is necessary to incorporate the strong depolarizing effect of multiple scattering near the horizon. Singularity theory is compared with new digital images of sky polarization, and gives an excellent description of the pattern of polarization directions. For the intensity of polarization, the theory can reproduce not only the zeros but also subtle variations in the polarization maxima

The search for exudates from Eurasian watermilfoil and hydrilla

Secondary metabolites are produced by aquatic plants, and in some instances, exudation of these metabolites into the surrounding water has been detected. To determine whether infestations of Eurasian watermilfoil or hydrilla produce such exudates, plant tissues and water samples were collected from laboratory cultures and pond populations and were analyzed using solid phase extraction, HPLC, and various methods of mass spectrometry including electrospray ionization, GC/MS, electron impact and chemical ionization. Previously reported compounds such as tellimagrandin II (from Eurasian watermilfoil) and a caffeic acid ester (from hvdrilla), along with a newly discovered flavonoid, cyanidin 3 dimalonyl glucoside (from hydrilla), were readily detected in plant tissues used in this research but were not detected in any of the water samples. If compounds are being released, as suggested by researchers using axenic cultures, we hypothesize that they may be rapidly degraded by bacteria and therefore undetectable

Managing Electrotechnology Innovation in the USA

In 1982, IIASA initiated an Innovation Management Task that brought together many leading managers from the electrotechnology industry as well as researchers and policy makers. This endeavor resulted in several meetings with the active participation and support of representatives from industry from both East and West. The first of these meetings, of which Electrosila was one of the supporting organizations, took place in Leningrad in May 1982. This meeting also identified the focus of those future activities that were esteemed to be of predominant importance for managers in the electrotechnology industry. These included the strategic development of a company, and the human and organizational factors in managing innovation. In this paper, the author presents an overview of innovation management in the United States electrotechnology industry from an historical perspective. He touches on all three factors that were recommended at the Leningrad meeting and describes them from the point of view of his many years of first-hand experience and direct involvement. Further, he describes the role of the user in as much as it significantly affects the technical development of the industry. The paper describes in clear, concise scientific terms the interaction of new technologies and the economy of industrial performance as well as national policy and its impact on the overall development. This paper will be of interest not only to policy researchers, but also to managers from industry and decision makers in government. It is also a welcome sign to all former participants in the innovation management meetings that IIASA strongly supports this activity

Theory of Magneto--Acoustic Transport in Modulated Quantum Hall Systems Near ν=1/2\nu=1/2

Motivated by the experimental results of Willett et al [Phys.Rev. Lett., {\bf 78}, 4478 (1997)] we develop a magneto-transport theory for the response of a two dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near Landau level filling factor $\nu = 1/2$ to the surface acoustic wave (SAW) in the presence of an added periodic density modulation. We assume there exists a Composite Fermion Fermi Surface (CF-FS) at $\nu = 1/2$, and we show that the deformation of the (CF-FS) due to the density modulation can be at the origin of the observed transport anomalies for the experimental conditions. Our analysis is carried out particularly for the non-local case which corresponds to the SAW experiments. We introduce a new model of a deformed CF-FS. The model permits us to explain anomalous features of the response of the modulated 2DEG to the SAW near $\nu = 1/2:$ namely the nonlinear wave vector dependence of the electron conductivity, the appearance of peaks in the SAW velocity shift and attenuation and the anisotropy of the effect, all of which originate from contributions to the conductivity tensor due to the regions of the CF-FS which are flattened by the applied modulation.Comment: 13 pages, 4 figures, the published versio

Investigation of scaling properties of hysteresis in Finemet thin films

We study the behavior of hysteresis loops in Finemet Fe$_{73.5}$Cu$_1$Nb$_3$Si$_{18.5}$B$_4$ thin films by using a fluxometric setup based on a couple of well compensated pickup coils. The presence of scaling laws of the hysteresis area is investigated as a function of the amplitude and frequency of the applied field, considering sample thickness from about 20 nm to 5 $\mu$m. We do not observe any scaling predicted by theoretical models, while dynamic loops show a logarithmic dependence on the frequency.Comment: 2 pages, 2 figure

Universal Behaviour of Metal-Insulator Transitions in the p-SiGe System

Magnetoresistance measurements are presented for a strained p-SiGe quantum well sample where the density is varied through the B=0 metal-insulator transition. The close relationship between this transition, the high field Hall insulator transition and the filling factor $\nu$=3/2 insulating state is demonstrated.Comment: 6 pages, 4 figures. Submitted to EP2DS XIII conference 199

From Tetraquark to Hexaquark: A Systematic Study of Heavy Exotics in the Large NcN_c Limit

A systematic study of multiquark exotics with one or $N_c-1$ heavy quarks in the large $N_c$ limit is presented. By binding a chiral soliton to a heavy meson, either a normal $N_c$-quark baryon or an exotic $(N_c+2)$-quark baryon is obtained. By replacing the heavy quark with $N_c-1$ heavy antiquarks, exotic $(2N_c-2)$-quark and $2N_c$-quark mesons are obtained. When $N_c = 3$, they are just the normal triquark baryon $Qqq$, the exotic pentaquark baryon $Q\bar q\bar q\bar q\bar q$, tetraquark di-meson $\bar Q \bar Q qq$ and the hexaquark di-baryon $\bar Q \bar Q \bar q \bar q\ bar q \bar q$ respectively. Their stabilities and decays are also discussed. In particular, it is shown that the ``heavy to heavy'' semileptonic decays are described by the Isgur--Wise form factors of the normal baryons.Comment: 14 pages in REVTeX, no Figure

Another tetraquark structure in the π+χc1\pi^+ \chi_{c1} invariant mass distribution

In this article, we assume that there exists a scalar hidden charm tetraquark state in the $\pi^+ \chi_{c1}$ invariant mass distribution, and study its mass using the QCD sum rules. The numerical result $M_{Z}=(4.36\pm0.18) \rm{GeV}$ is consistent with the mass of the Z(4250). The Z(4250) may be a tetraquark state, other possibilities, such as a hadro-charmonium resonance and a $D_1^+\bar{D}^0+ D^+\bar{D}_1^0$ molecular state are not excluded.Comment: 14 pages, 14 figure, correct some type error

MIMO free-space optical communication employing subcarrier intensity modulation in atmospheric turbulence channels

In this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects

Antarctic station-based seasonal pressure reconstructions since 1905: 2. Variability and trends during the twentieth century

The Antarctic seasonal station-based pressure reconstructions evaluated in our companion paper are evaluated here to provide additional knowledge on Antarctic pressure variability during the twentieth century. In the period from 1905 to 1956, we find that the Hadley Centre gridded sea level pressure data set compared the best with our reconstructions, perhaps due to similar methods to estimate pressure without direct observations. The primary focus on the twentieth century Antarctic pressure variability was in summer and winter, as these were the seasons with the highest reconstruction skill. In summer, there is considerable interannual variability that was spatially uniform across all of Antarctica. Notable high pressure anomalies were found in the summers of 1911/1912 and 1925/1926; both summers correspond to negative phases of the Southern Annular Mode as well as El Niño events in the tropical Pacific. In addition, negative summer pressure trends during the last ~40 years across all of Antarctica are unique in the context of 30 year trends throughout the entire twentieth century, suggesting a strong component of anthropogenic forcing on the recent summer trends. In contrast, mean winter pressure is less variable from year to year during the early twentieth century, and there is less similarity between the pressure variations along the Antarctic Peninsula compared to the rest of the continent. No significant pressure trends were found consistently across all Antarctica (although some significant regional trends can be identified), and low-frequency, multidecadal-scale variability appears to dominate the historical pressure variations in this season