Fast Characterization of Dispersion and Dispersion Slope of Optical Fiber Links using Spectral Interferometry with Frequency Combs

We demonstrate fast characterization (~1.4 microseconds) of both the dispersion and dispersion slope of long optical fiber links (~25 km) using dual quadrature spectral interferometry with an optical frequency comb. Compared to previous spectral interferometry experiments limited to fiber lengths of meters, the long coherence length and the periodic delay properties of frequency combs, coupled with fast data acquisition, enable spectral interferometric characterization of fibers longer by several orders of magnitude. We expect that our method will be useful to recently proposed lightwave techniques like coherent WDM and to coherent modulation formats by providing a real time monitoring capability for the link dispersion. Another area of application would be in stabilization of systems which perform frequency and timing distribution over long fiber links using stabilized optical frequency combs.Comment: 3 pages, 3 figures, Minor changes to tex

Compton scattering of electrons in the intergalactic medium

This paper investigates the distribution and implications of cosmic ray electrons within the intergalactic medium (IGM). Utilizing a synthesis model of the extragalactic background, we evolve the spectrum of Compton-included cosmic rays. The energy density distribution of cosmic ray electrons peaks at redshift $z \approx2$, and peaks in the $\sim$MeV range. The fractional contribution of cosmic ray pressure to the general IGM pressure progressively increases toward lower redshift. At mean density, the ratio of cosmic ray electron to thermal pressure in the IGM $P_{\rm CRe} / P_{\rm th}$ is 0.3% at $z=2$, rising to 1.0% at $z=1$, and 1.8% at $z=0.1$ (considering only the cosmic rays produced locally by Compton scattering). We compute the linear Landau damping rate of plasma oscillations in the IGM caused by the $\sim$MeV cosmic ray electrons, and find it to be of order $\sim 10^{-6}\,\rm s^{-1}$ for wavenumbers $1.2\lesssim ck/\omega_{\rm p}\lesssim 5$ at $z=2$ and mean density (where $\omega_{\rm p}$ is the plasma frequency). This strongly affects the fate of TeV $e^+e^-$ pair beams produced by blazars, which are potentially unstable to oblique instabilities involving plasma oscillations with wavenumber $ck/\omega_{\rm p}\approx\sec\theta$ ($\theta$ being the angle between the beam and wave vector). Linear Landau damping is at least thousands of times faster than either pair beam instability growth or collisional effects; it thus turns off the pair beam instability except for modes with very small $\theta$ ($ck/\omega_{\rm p}\rightarrow 1$, where linear Landau damping is kinematically suppressed). This leaves open the question of whether the pair beam instability is turned off entirely, or can still proceed via the small-$\theta$ modes.Comment: 22 pages, 9 figure

Gaussian-shaped Optical Frequency Comb Generation for Microwave Photonic Filtering

Using only electro-optic modulators, we generate a 41-line 10-GHz Gaussian-shaped optical frequency comb. We use this comb to demonstrate apodized microwave photonic filters with greater than 43-dB sidelobe suppression without the need for a pulse shaper.Comment: 3 pages, 4 figure

Nanobubbles Provide Theranostic Relief to Cancer Hypoxia

Hypoxia is a common motif among tumors, contributing to metastasis, angiogenesis, cellular epigenetic abnormality, and resistance to cancer therapy. Hypoxia also plays a pivotal role in oncological studies, where it can be used as a principal target for new anti-cancer therapeutic methods. Oxygen nanobubbles were designed in an effort to target the hypoxic tumor regions, thus interrupting the hypoxia-inducible factor-1α (HIF-1α) regulatory pathway and inhibiting tumor progression. At less than 100nm, oxygen nanobubbles act as a vehicle for site-specific oxygen delivery, while also serving as an ultrasound contrast agent for advanced imaging purposes. Through in vitro and in vivo studies, it was shown the reversal of 5mC hypomethylation was achieved in the hypoxia-afflicted regions. An obvious increase in the oxygen concentration within hypoxic regions was also observed, implying adequate oxygen dissociation from the nanobubbles to the hypoxic tumor microenvironment. These implications suggest nanobubbles can be used as a means for epigenetic regulation, ultrasound imaging, and cancer therapeutics, thus having a significant impact on new-age cancer treatment methods in oncology

Comment on the Nanoparticle Conclusions in Crüts et al. (2008), "Exposure to diesel exhaust induces changes in EEG in human volunteers"

A recent publication in this journal reported interesting changes in electroencephalographic (EEG) waves that occurred in 10 young, male volunteers following inhalation for one hour of elevated levels of diesel-engine exhaust fumes [1]. The authors then proposed a chain of causal events that they hypothesized underlay their observed EEG changes. Their reasoning linked the observed results to nanoparticles in diesel-engine exhaust (DEE), and went on to suggest that associations between changes in ambient particulate matter (PM) levels and changes in health statistics might be due to the effects of diesel-engine exhaust (DEE) nanoparticles on EEG. We suggest that the extrapolations of the Crüts et al. EEG findings to casual mechanisms about how ambient levels of DEE particulate might affect electrical signals in the brain, and subsequently to how DEE particulate might alter disease risk, are premature

Lyman-α\alpha polarization from cosmological ionization fronts: II. Implications for intensity mapping

This is the second paper in a series whose aim is to predict the power spectrum of intensity and polarized intensity from cosmic reionization fronts. After building the analytic models for intensity and polarized intensity calculations in paper I, here we apply these models to simulations of reionization. We construct a geometric model for identifying front boundaries, calculate the intensity and polarized intensity for each front, and compute a power spectrum of these results. This method was applied to different simulation sizes and resolutions, so we ensure that our results are convergent. We find that the power spectrum of fluctuations at $z=8$ in a bin of width $\Delta z=0.5$ ($\lambda/\Delta\lambda=18$) is $\Delta_\ell \equiv [\ell(\ell+1)C_\ell/2\pi]^{1/2}$ is $3.2\times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the intensity $I$, $7.6\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the $E$-mode polarization, and $5.8\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the $B$-mode polarization at $\ell=1.5\times10^4$. After computing the power spectrum, we compare results to detectable scales and discuss implications for observing this signal based on a proposed experiment. We find that, while fundamental physics does not exclude this kind of mapping from being attainable, an experiment would need to be highly ambitious and require significant advances to make mapping Lyman-$\alpha$ polarization from cosmic reionization fronts a feasible goal.Comment: 18 pages, 9 figures, to be submitted to JCA

Lyman-{\alpha} polarization from cosmological ionization fronts: I. Radiative transfer simulations

In this paper, we present the formalism of simulating Lyman-$\alpha$ emission and polarization around reionization ($z$ = 8) from a plane-parallel ionization front. We accomplish this by using a Monte Carlo method to simulate the production of a Lyman-$\alpha$ photon, its propagation through an ionization front, and the eventual escape of this photon. This paper focuses on the relation of the input parameters of ionization front speed $U$, blackbody temperature $T_{\rm bb}$, and neutral hydrogen density $n_{\rm HI}$, on intensity $I$ and polarized intensity $P$ as seen by a distant observer. The resulting values of intensity range from $3.18\times 10^{-14}$ erg/cm$^{2}$/s/sr to $1.96 \times 10^{-9}$ erg/cm$^{2}$/s/sr , and the polarized intensity ranges from $5.73\times 10^{-17}$ erg/cm$^{2}$/s/sr to $5.31 \times 10^{-12}$ erg/cm$^{2}$/s/sr. We found that higher $T_{\rm bb}$, higher $U$, and higher $n_{\rm HI}$ contribute to higher intensity, as well as polarized intensity, though the strongest dependence was on the hydrogen density. The dependence of viewing angle of the front is also explored. We present tests to support the validity model, which makes the model suitable for further use in a following paper where we will calculate the intensity and polarized intensity power spectrum on a full reionization simulation.Comment: 29 pages, 13 figures, to be submitted to JCA