80 research outputs found
Effects of self- and cross-phase modulation on the spontaneous symmetry breaking of light in ring resonators
We describe spontaneous symmetry breaking in the powers of two optical modes
coupled into a ring resonator, using a pair of coupled Lorentzian equations,
featuring tunable self- and cross-phase modulation terms. We investigate a wide
variety of nonlinear materials by changing the ratio of the self- and
cross-phase interaction coefficients. Static and dynamic effects range from the
number and stability of stationary states to the onset and nature of
oscillations. Minimal conditions to observe symmetry breaking are provided in
terms of the ratio of the self-/cross-phase coefficients, detuning, and input
power. Different ratios of the nonlinear coefficients also influence the
dynamical regime, where they can induce or suppress bifurcations and
oscillations. A generalised description on this kind is useful for the
development of all-optical components, such as isolators and oscillators,
constructed from a wide variety of optical media in ring resonators.Comment: 10 pages, 10 figure
Interplay of Polarization and Time-Reversal Symmetry Breaking in Synchronously Pumped Ring Resonators
Optically induced breaking of symmetries plays an important role in nonlinear
photonics, with applications ranging from optical switching in integrated
photonic circuits to soliton generation in ring lasers. In this work we study
for the first time the interplay of two types of spontaneous symmetry breaking
that can occur simultaneously in optical ring resonators. Specifically we
investigate a ring resonator (e.g. a fiber loop resonator or whispering gallery
microresonator) that is synchronously pumped with short pulses of light. In
this system we numerically study the interplay and transition between regimes
of temporal symmetry breaking (in which pulses in the resonator either run
ahead or behind the seed pulses) and polarization symmetry breaking (in which
the resonator spontaneously generates elliptically polarized light out of
linearly polarized seed pulses). We find ranges of pump parameters for which
each symmetry breaking can be independently observed, but also a regime in
which a dynamical interplay takes place. Besides the fundamentally interesting
physics of the interplay of different types of symmetry breaking, our work
contributes to a better understanding of the nonlinear dynamics of optical ring
cavities which are of interest for future applications including all-optical
logic gates, synchronously pumped optical frequency comb generation, and
resonator-based sensor technologies
Coherent suppression of backscattering in optical microresonators
As light propagates along a waveguide, a fraction of the field can be reflected by Rayleigh scatterers. In high quality-factor whispering-gallery-mode microresonators, this intrinsic backscattering is primarily caused by either surface or bulk material imperfections. For several types of microresonator-based experiments and applications, minimal backscattering in the cavity is of critical importance, and thus the ability to suppress the backscattering is essential. We demonstrate that introducing an additional scatterer in the near-field of a high-quality-factor microresonator can coherently suppress the amount of backscattering in a microresonator by more than 30 dB. The method relies on controlling the scatterer's position in order for the intrinsic and scatterer-induced backpropagating fields to destructively interfere. This technique is useful in microresonator applications where backscattering is currently limiting the performance of devices, such as ring-laser gyroscopes and dual frequency combs that both suffer from injection locking. Moreover, these findings are of interest for integrated photonic circuits in which backreflections could negatively impact the stability of laser sources or other components
Probing the Intermediate-Age Globular Clusters in NGC 5128 from Ultraviolet Observations
We explore the age distribution of the globular cluster (GC) system of the
nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from Galaxy
Evolution Explorer (GALEX) observations, with UV - optical colors used as the
age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and
Milky Way in UV - optical color-color diagram, which indicates that the
majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31
and Milky Way. A large fraction of spectroscopically identified
intermediate-age GC (IAGC) candidates with ~ 3-8 Gyr are not detected in the
FUV passband. Considering the nature of intermediate-age populations being
faint in the far-UV (FUV) passband, we suggest that many of the
spectroscopically identified IAGCs may be truly intermediate in age. This is in
contrast to the case of M31 where a large fraction of spectroscopically
suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but
rather older GCs with developed blue horizontal branch stars. Our UV photometry
strengthens the results previously suggesting the presence of GC and stellar
subpopulation with intermediate age in NGC 5128. The existence of IAGCs
strongly indicates the occurrence of at least one more major star formation
episode after a starburst at high redshift.Comment: 8 pages, 3 figures, accepted for ApJ Lette
Primary skin fibroblasts as a model of Parkinson's disease
Parkinson's disease is the second most frequent neurodegenerative disorder. While most cases occur sporadic mutations in a growing number of genes including Parkin (PARK2) and PINK1 (PARK6) have been associated with the disease. Different animal models and cell models like patient skin fibroblasts and recombinant cell lines can be used as model systems for Parkinson's disease. Skin fibroblasts present a system with defined mutations and the cumulative cellular damage of the patients. PINK1 and Parkin genes show relevant expression levels in human fibroblasts and since both genes participate in stress response pathways, we believe fibroblasts advantageous in order to assess, e.g. the effect of stressors. Furthermore, since a bioenergetic deficit underlies early stage Parkinson's disease, while atrophy underlies later stages, the use of primary cells seems preferable over the use of tumor cell lines. The new option to use fibroblast-derived induced pluripotent stem cells redifferentiated into dopaminergic neurons is an additional benefit. However, the use of fibroblast has also some drawbacks. We have investigated PARK6 fibroblasts and they mirror closely the respiratory alterations, the expression profiles, the mitochondrial dynamics pathology and the vulnerability to proteasomal stress that has been documented in other model systems. Fibroblasts from patients with PARK2, PARK6, idiopathic Parkinson's disease, Alzheimer's disease, and spinocerebellar ataxia type 2 demonstrated a distinct and unique mRNA expression pattern of key genes in neurodegeneration. Thus, primary skin fibroblasts are a useful Parkinson's disease model, able to serve as a complement to animal mutants, transformed cell lines and patient tissues
Survival and Passage of Yearling and Subyearling Chinook Salmon and Juvenile Steelhead at McNary Dam, 2012
The study was designed to evaluate the passage and survival of yearling and subyearling Chinook salmon and juvenile steelhead at McNary Dam as stipulated by the 2008 Biological Opinion and Fish Accords and to assess performance measures including route-specific fish passage proportions, travel times, and survival based upon a virtual/paired-release model. This study supports the USACE’s continual effort to improve conditions for juvenile anadromous fish passing through Columbia River dams
Survival and Passage of Yearling Chinook Salmon and Steelhead at The Dalles Dam, Spring 2011 - FINAL REPORT
The study reported herein was conducted by the Pacific Northwest National Laboratory (PNNL) and the University of Washington (UW) for the U.S. Army Corps of Engineers, Portland District (USACE). The PNNL and UW project managers were Drs. Thomas J. Carlson and John R. Skalski, respectively. The USACE technical lead was Mr. Brad Eppard. The study was designed to estimate dam passage survival and other performance measures at The Dalles Dam as stipulated by the 2008 Federal Columbia River Power System Biological Opinion (BiOp) and the 2008 Columbia Basin Fish Accords. The study is being documented in two types of reports: compliance and technical. A compliance report is delivered within 6 months of the completion of the field season and focuses on results of the performance metrics outlined in the 2008 BiOp and Fish Accords. A technical report is produced within the 18 months after field work, providing comprehensive documentation of a given study and results on route-specific survival estimates and fish passage distributions, which are not included in compliance reports. This technical report concerns the 2011 acoustic telemetry study at The Dalles Dam
Capacity shortfalls hinder the performance of marine protected areas globally
Marine protected areas (MPAs) are increasingly being used globally to conserve marine resources. However, whether many MPAs are being effectively and equitably managed, and how MPA management influences substantive outcomes remain unknown. We developed a global database of management and fish population data (433 and 218 MPAs, respectively) to assess: MPA management processes; the effects of MPAs on fish populations; and relationships between management processes and ecological effects. Here we report that many MPAs failed to meet thresholds for effective and equitable management processes, with widespread shortfalls in staff and financial resources. Although 71% of MPAs positively influenced fish populations, these conservation impacts were highly variable. Staff and budget capacity were the strongest predictors of conservation impact: MPAs with adequate staff capacity had ecological effects 2.9 times greater than MPAs with inadequate capacity. Thus, continued global expansion of MPAs without adequate investment in human and financial capacity is likely to lead to sub-optimal conservation outcomes
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