A compact spectroradiometer for solar simulator measurements

Compact spectral irradiance probe has been designed and built which uses wedge filter in conjunction with silicon cell and operational amplifier. Probe is used to monitor spectral energy distribution of solar simulators and other high intensity sources

Nonlinear Electron Oscillations in a Viscous and Resistive Plasma

New non-linear, spatially periodic, long wavelength electrostatic modes of an electron fluid oscillating against a motionless ion fluid (Langmuir waves) are given, with viscous and resistive effects included. The cold plasma approximation is adopted, which requires the wavelength to be sufficiently large. The pertinent requirement valid for large amplitude waves is determined. The general non-linear solution of the continuity and momentum transfer equations for the electron fluid along with Poisson's equation is obtained in simple parametric form. It is shown that in all typical hydrogen plasmas, the influence of plasma resistivity on the modes in question is negligible. Within the limitations of the solution found, the non-linear time evolution of any (periodic) initial electron number density profile n_e(x, t=0) can be determined (examples). For the modes in question, an idealized model of a strictly cold and collisionless plasma is shown to be applicable to any real plasma, provided that the wavelength lambda >> lambda_{min}(n_0,T_e), where n_0 = const and T_e are the equilibrium values of the electron number density and electron temperature. Within this idealized model, the minimum of the initial electron density n_e(x_{min}, t=0) must be larger than half its equilibrium value, n_0/2. Otherwise, the corresponding maximum n_e(x_{max},t=tau_p/2), obtained after half a period of the plasma oscillation blows up. Relaxation of this restriction on n_e(x, t=0) as one decreases lambda, due to the increase of the electron viscosity effects, is examined in detail. Strong plasma viscosity is shown to change considerably the density profile during the time evolution, e.g., by splitting the largest maximum in two.Comment: 16 one column pages, 11 figures, Abstract and Sec. I, extended, Sec. VIII modified, Phys. Rev. E in pres

Terabit communications – tasks, challenges, and the impact of disruptive technologies

Throughout history, effective communication has been of THE most critical importance to all civilisations, the means employed being underpinned and enabled by the greatest scientific breakthroughs of the age. Today we live in an information age and consequently there is a growing need to send vast amounts of data both securely and at the shortest time possible across the globe. However, to keep pace with this demand it is critical that the capacity of future communication networks is able to perform accordingly. However it is an open secret that to achieve this is becoming an increasingly difficult task. In this paper we explore key technological milestones and breakthroughs that have enabled to support rapidly the growing demand for data. This will be followed by a discussion of the drivers of this demand, the socio-political consequences of this development, and the technical challenges we must overcome if demand is to be met into the future. These technical challenges encompass issues of CMOS scalability, power consumption, and data centres & network switching abilities

The rising role of photonics in today's data centres

In recent years there has been a rapid growth in demand for ultra high speed data transmission with end users expecting fast, high bandwidth network access. This growth has put data centres under increasing pressure to provide greater data throughput and ever increasing data rates while at the same time improving the quality of data handling in terms of reduced latency, increased scalability and improved channel speed for users. However, data networks are becoming increasingly difficult to scale to meet this growing demand using current well established CMOS technology and architectures. As a result electronic bottlenecks are becoming apparent despite improvements in data management. The inter-related issues of electronic scalability, power consumption, copper interconnect bandwidth and the limited speed of CMOS electronics will be discussed; and the tremendous potential of optical fibre based networks to provide the necessary bandwidth will be illustrated. In addition, some applications of photonics to alleviate speed, throughput and latency issues in data networks will be discussed. Finally, progress in the form of a novel and highly scalable optical interconnect will be reviewed

The LSST Data Mining Research Agenda

We describe features of the LSST science database that are amenable to scientific data mining, object classification, outlier identification, anomaly detection, image quality assurance, and survey science validation. The data mining research agenda includes: scalability (at petabytes scales) of existing machine learning and data mining algorithms; development of grid-enabled parallel data mining algorithms; designing a robust system for brokering classifications from the LSST event pipeline (which may produce 10,000 or more event alerts per night); multi-resolution methods for exploration of petascale databases; indexing of multi-attribute multi-dimensional astronomical databases (beyond spatial indexing) for rapid querying of petabyte databases; and more.Comment: 5 pages, Presented at the "Classification and Discovery in Large Astronomical Surveys" meeting, Ringberg Castle, 14-17 October, 200

Scotland, Catalonia and the “right” to self-determination: a comment suggested by Kathryn Crameri’s “Do Catalans Have the Right to Decide?

No abstract available

Nonlinear electrostatic oscillations in a cold magnetized electron-positron plasma

We study the spatio-temporal evolution of the nonlinear electrostatic oscillations in a cold magnetized electron-positron (e-p) plasma using both analytics and simulations. Using a perturbative method we demonstrate that the nonlinear solutions change significantly when a pure electrostatic mode is excited at the linear level instead of a mixed upper-hybrid and zero-frequency mode that is considered in a recent study. The pure electrostatic oscillations undergo phase mixing nonlinearly. However, the presence of the magnetic field significantly delays the phase-mixing compared to that observed in the corresponding unmagnetized plasma. Using 1D PIC simulations we then analyze the damping of the primary modes of the pure oscillations in detail and infer the dependence of the phase-mixing time on the magnetic field and the amplitude of the oscillations. The results are remarkably different from those found for the mixed upper-hybrid mode mentioned above. Exploiting the symmetry of the e-p plasma we then explain a generalized symmetry of our non-linear solutions. The symmetry allows us to construct a unique nonlinear solution up to the second order which does not show any signature of phase mixing but results in a nonlinear wave traveling at upper-hybrid frequency. Our investigations have relevance for laboratory/astrophysical e-p plasmas

Vibrational Tamm states at the edges of graphene nanoribbons

We study vibrational states localized at the edges of graphene nanoribbons. Such surface oscillations can be considered as a phonon analog of Tamm states well known in the electronic theory. We consider both armchair and zigzag graphene stripes and demonstrate that surface modes correspond to phonons localized at the edges of the graphene nanoribbon, and they can be classified as in-plane and out-of-plane modes. In addition, in armchair nanoribbons anharmonic edge modes can experience longitudinal localization in the form of self-localized nonlinear modes, or surface breather solitons.Comment: 10 pages, 10 figure

Differential coupling of G protein alpha subunits to seven-helix receptors expressed in Xenopus oocytes

Xenopus oocytes were used to examine the coupling of the serotonin 1c (5HT1c) and thyrotropin-releasing hormone (TRH) receptors to both endogenous and heterologously expressed G protein alpha subunits. Expression of either G protein-coupled receptor resulted in agonist- induced, Ca(2+)-activated Cl- currents that were measured using a two- electrode voltage clamp. 5HT-induced Cl- currents were reduced 80% by incubating the injected oocytes with pertussis toxin (PTX) and inhibited 50-65% by injection of antisense oligonucleotides to the PTX- sensitive Go alpha subunit. TRH-induced Cl- currents were reduced only 20% by PTX treatment but were inhibited 60% by injection of antisense oligonucleotides to the PTX-insensitive Gq alpha subunit. Injection of antisense oligonucleotides to a novel Xenopus phospholipase C-beta inhibited the 5HT1c (and Go)-induced Cl- current with little effect on the TRH (and Gq)-induced current. These results suggest that receptor- activated Go and Gq interact with different effectors, most likely different isoforms of phospholipase C-beta. Co-expression of each receptor with seven different mammalian G protein alpha subunit cRNAs (Goa, Gob, Gq, G11, Gs, Golf, and Gt) was also examined. Co-expression of either receptor with the first four of these G alpha subunits resulted in a maximum 4-6-fold increase in Cl- currents; the increase depended on the amount of G alpha subunit cRNA injected. This increase was blocked by PTX for G alpha oa and G alpha ob co-expression but not for G alpha q or G alpha 11 co-expression. Co-expression of either receptor with Gs, Golf, or Gt had no effect on Ca(2+)-activated Cl- currents; furthermore, co-expression with Gs or Golf also failed to reveal 5HT- or TRH-induced changes in adenylyl cyclase as assessed by activation of the cystic fibrosis transmembrane conductance regulator Cl- channel. These results indicate that in oocytes, the 5HT1c and TRH receptors do the following: 1) preferentially couple to PTX-sensitive (Go) and PTX-insensitive (Gq) G proteins and that these G proteins act on different effectors, 2) couple within the same cell type to several different heterologously expressed G protein alpha subunits to activate the oocyte's endogenous Cl- current, and 3) fail to couple to G protein alpha subunits that activate cAMP or phosphodiesterase