Robust low loss splicing of hollow core photonic bandgap fiber to itself

Robust, low loss (0.16dB) splicing of hollow core photonic band gap fiber to itself is presented. Modal content is negligibly affected by splicing, enabling penalty-free 40Gbit/s data transmission over > 200m of spliced PBGF

The potential of effective field theory in NN scattering

We study an effective field theory of interacting nucleons at distances much greater than the pion's Compton wavelength. In this regime the NN potential is conjectured to be the sum of a delta function and its derivatives. The question we address is whether this sum can be consistently truncated at a given order in the derivative expansion, and systematically improved by going to higher orders. Regularizing the Lippmann-Schwinger equation using a cutoff we find that the cutoff can be taken to infinity only if the effective range is negative. A positive effective range---which occurs in nature---requires that the cutoff be kept finite and below the scale of the physics which has been integrated out, i.e. O(m_\pi). Comparison of cutoff schemes and dimensional regularization reveals that the physical scattering amplitude is sensitive to the choice of regulator. Moreover, we show that the presence of some regulator scale, a feature absent in dimensional regularization, is essential if the effective field theory of NN scattering is to be useful. We also show that one can define a procedure where finite cutoff dependence in the scattering amplitude is removed order by order in the effective potential. However, the characteristic momentum in the problem is given by the cutoff, and not by the external momentum. It follows that in the presence of a finite cutoff there is no small parameter in the effective potential, and consequently no systematic truncation of the derivative expansion can be made. We conclude that there is no effective field theory of NN scattering with nucleons alone.Comment: 25 pages LaTeX, 3 figures (uses epsf

Complementary analysis of modal content and properties in a 19-cell hollow core photonic band gap fiber using Time-of-Flight and S2 techniques

We study the rich multimode content of an ultra-low loss hollow core photonic bandgap fiber using two complementary techniques which allow us to investigate both short and long propagation distances. Several distinct vector modes are clearly identified, with evidence of low intermodal coupling and distributed scattering

1.45 Tbit/s low latency data transmission through 19-cell hollow core photonic band gap fibre

We report transmission of 37 x 40 Gbit/s C-band channels over 250 m of hollow core band gap fibre, at 99.7% the speed of light in vacuum. BER penalty below 1 dB as compared to back-to-back was measured across the C-band

Mitigating spectral leakage and sampling errors in spatial and spectral (S2) imaging

We present a novel method for validating the relative power value (MPI) of the Spatial and Spectral (S2) imaging technique. By applying corrections for spectral leakage and sampling errors we found the MPI determinations to be accurate within 1dB

Surface Roughness and Effective Stick-Slip Motion

The effect of random surface roughness on hydrodynamics of viscous incompressible liquid is discussed. Roughness-driven contributions to hydrodynamic flows, energy dissipation, and friction force are calculated in a wide range of parameters. When the hydrodynamic decay length (the viscous wave penetration depth) is larger than the size of random surface inhomogeneities, it is possible to replace a random rough surface by effective stick-slip boundary conditions on a flat surface with two constants: the stick-slip length and the renormalization of viscosity near the boundary. The stick-slip length and the renormalization coefficient are expressed explicitly via the correlation function of random surface inhomogeneities. The effective stick-slip length is always negative signifying the effective slow-down of the hydrodynamic flows by the rough surface (stick rather than slip motion). A simple hydrodynamic model is presented as an illustration of these general hydrodynamic results. The effective boundary parameters are analyzed numerically for Gaussian, power-law and exponentially decaying correlators with various indices. The maximum on the frequency dependence of the dissipation allows one to extract the correlation radius (characteristic size) of the surface inhomogeneities directly from, for example, experiments with torsional quartz oscillators.Comment: RevTeX4, 14 pages, 3 figure

Lattice calculation of 1−+1^{-+} hybrid mesons with improved Kogut-Susskind fermions

We report on a lattice determination of the mass of the exotic $1^{-+}$ hybrid meson using an improved Kogut-Susskind action. Results from both quenched and dynamical quark simulations are presented. We also compare with earlier results using Wilson quarks at heavier quark masses. The results on lattices with three flavors of dynamical quarks show effects of sea quarks on the hybrid propagators which probably result from coupling to two meson states. We extrapolate the quenched results to the physical light quark mass to allow comparison with experimental candidates for the $1^{-+}$ hybrid meson. The lattice result remains somewhat heavier than the experimental result, although it may be consistent with the $\pi_1(1600)$.Comment: 24 pages, 12 figures. Replaced to match published versio

Vortex Plastic Flow, B(x,y,H(t)),M(H(t)),Jc(B(t))B(x,y,H(t)), M(H(t)), J_c(B(t)), Deep in the Bose Glass and Mott-Insulator Regimes

We present simulations of flux-gradient-driven superconducting vortices interacting with strong columnar pinning defects as an external field $H(t)$ is quasi-statically swept from zero through a matching field $B_{\phi}$. We analyze several measurable quantities, including the local flux density $B(x,y,H(t))$, magnetization $M(H(t))$, critical current $J_{c}(B(t))$, and the individual vortex flow paths. We find a significant change in the behavior of these quantities as the local flux density crosses $B_{\phi}$, and quantify it for many microscopic pinning parameters. Further, we find that for a given pin density $J_c(B)$ can be enhanced by maximizing the distance between the pins for $B < B_{\phi}$.Comment: 4 pages, 4 PostScript Figure

Observations of the temporal variability in aerosol properties and their relationships to meteorology in the summer monsoonal South China Sea/East Sea: the scale-dependent role of monsoonal flows, the Madden-Julian Oscillation, tropical cyclones, squall lines and cold pools

The article of record as published may be located at http://dx.doi.org/10.5194/acp-15-1745-2015In a joint NRL/Manila Observatory mission, as part of the Seven SouthEast Asian Studies program (7- SEAS), a 2-week, late September 2011 research cruise in the northern Palawan archipelago was undertaken to observe the nature of southwest monsoonal aerosol particles in the South China Sea/East Sea (SCS/ES) and Sulu Sea region. Previous analyses suggested this region as a receptor for biomass burning from Borneo and Sumatra for boundary layer air entering the monsoonal trough. Anthropogenic pollution and biofuel emissions are also ubiquitous, as is heavy shipping traffic. Here, we provide an overview of the regional environment during the cruise, a time series of key aerosol and meteorological parameters, and their interrelationships. Overall, this cruise provides a narrative of the processes that control regional aerosol loadings and their possible feedbacks with clouds and precipitation. While 2011 was a moderate El Niño–Southern Oscillation (ENSO) La Niña year, higher burning activity and lower precipitation was more typical of neutral conditions. The large-scale aerosol environment was modulated by the Madden–Julian Oscillation (MJO) and its associated tropical cyclone (TC) activity in a manner consistent with the conceptual analysis performed by Reid et al. (2012). Advancement of the MJO from phase 3 to 6 with accompanying cyclogenesis during the cruise period strengthened flow patterns in the SCS/ES that modulated aerosol life cycle. TC inflow arms of significant convection sometimes span from Sumatra to Luzon, resulting in very low particle concentrations (minimum condensation nuclei CN 3000 cm-3 and non-sea-salt PM2:5 10–25 μgm-3). These cases corresponded with two different mechanisms of convection suppression: lower free-tropospheric dry-air intrusion from the Indian Ocean, and large-scale TC-induced subsidence. Veering vertical wind shear also resulted in aerosol transport into this region being mainly in the marine boundary layer (MBL), although lower free troposphere transport was possible on the western sides of Sumatra and Borneo. At the hourly time scale, particle concentrations were observed to be modulated by integer factors through convection and associated cold pools. Geostationary satellite observations suggest that convection often takes the form of squall lines, which are bowed up to 500 km across the monsoonal flow and 50 km wide. These squall lines, initiated by cold pools from large thunderstorms and likely sustained by a veering vertical wind shear and aforementioned mid-troposphere dry layers, propagated over 1500 km across the entirety of the SCS/ES, effectively cutting large swaths of MBL aerosol particles out of the region. Our conclusion is that while largescale flow patterns are very important in modulating convection, and hence in allowing long-range transport of smoke and pollution, more short-lived phenomena can modulate cloud condensation nuclei (CCN) concentrations in the region, resulting in pockets of clean and polluted MBL air. This will no doubt complicate large scale comparisons of aerosol– cloud interaction

Multiband tight-binding theory of disordered ABC semiconductor quantum dots: Application to the optical properties of alloyed CdZnSe nanocrystals

Zero-dimensional nanocrystals, as obtained by chemical synthesis, offer a broad range of applications, as their spectrum and thus their excitation gap can be tailored by variation of their size. Additionally, nanocrystals of the type ABC can be realized by alloying of two pure compound semiconductor materials AC and BC, which allows for a continuous tuning of their absorption and emission spectrum with the concentration x. We use the single-particle energies and wave functions calculated from a multiband sp^3 empirical tight-binding model in combination with the configuration interaction scheme to calculate the optical properties of CdZnSe nanocrystals with a spherical shape. In contrast to common mean-field approaches like the virtual crystal approximation (VCA), we treat the disorder on a microscopic level by taking into account a finite number of realizations for each size and concentration. We then compare the results for the optical properties with recent experimental data and calculate the optical bowing coefficient for further sizes