Efficient Kerr soliton comb generation in micro-resonator with interferometric back-coupling.

Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation. However, the conversion efficiency of the pump power into a soliton frequency comb typically remains below a few percent. We fabricate and characterize a hybrid Mach-Zehnder ring resonator geometry, consisting of a micro-ring resonator embedded in an additional cavity with twice the optical path length of the ring. The resulting interferometric back coupling enables to achieve an unprecedented control of the pump depletion: pump-to-frequency comb conversion efficiencies of up to 55% of the input pump power is experimentally demonstrated with a soliton crystal comb. We assess the robustness of the proposed on-chip geometry by generating a large variety of dissipative Kerr soliton combs, which require a lower amount of pump power to be accessed, when compared with an isolated micro-ring resonator with identical parameters. Micro-resonators with feedback enable accessing new regimes of coherent soliton comb generation, and are well suited for comb applications in astronomy, spectroscopy and telecommunications.

Localized structures formed through domain wall locking in cavity-enhanced second-harmonic generation.

We analyze the formation of localized structures in cavity-enhanced second-harmonic generation. We focus on the phase-matched limit, and consider that fundamental and generated waves have opposite signs of group velocity dispersion. We show that these states form due to the locking of domain walls connecting two stable homogeneous states of the system, and undergo collapsed snaking. We study the impact of temporal walk-off on the stability and dynamics of these localized states.

Geometric Induction in Chiral Superconductors.

We consider a number of effects due to the interplay of superconductivity, electromagnetism, and elasticity, which are unique for thin membranes of layered chiral superconductors. Some of them should be within the reach of present technology, and could be useful for characterizing materials. More speculatively, the enriched control of Josephson junctions they afford might find useful applications.

Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen.

Titanium-based alloys are susceptible to hydrogen embrittlement (HE), a phenomenon that deteriorates fatigue properties. Ti-6Al-4V is the most widely used titanium alloy and the effect of hydrogen embrittlement on fatigue crack growth (FCG) was investigated by carrying out crack propagation tests in air and high-pressure H2 environment. The FCG test in hydrogen environment resulted in a drastic increase in crack growth rate at a certain Δ K, with crack propagation rates up to 13 times higher than those observed in air. Possible reasons for such behavior were discussed in this paper. The relationship between FCG results in high-pressure H2 environment and microstructure was investigated by comparison with already published results of cast and forged Ti-6Al-4V. Coarser microstructure was found to be more sensitive to HE. Moreover, the electron beam melting (EBM) materials experienced a crack growth acceleration in-between that of cast and wrought Ti-6Al-4V.

Modulation Instability Induced Frequency Comb Generation in a Continuously Pumped Optical Parametric Oscillator.

Continuously pumped passive nonlinear cavities can be harnessed for the creation of novel optical frequency combs. While most research has focused on third-order "Kerr" nonlinear interactions, recent studies have shown that frequency comb formation can also occur via second-order nonlinear effects. Here, we report on the formation of quadratic combs in optical parametric oscillator (OPO) configurations. Specifically, we demonstrate that optical frequency combs can be generated in the parametric region around half of the pump frequency in a continuously driven OPO. We also model the OPO dynamics through a single time-domain mean-field equation, identifying previously unknown dynamical regimes, induced by modulation instabilities, which lead to comb formation. Numerical simulation results are in good agreement with experimentally observed spectra. Moreover, the analysis of the coherence properties of the simulated spectra shows the existence of correlated and phase-locked combs. Our results reveal previously unnoticed dynamics of an apparently well assessed optical system, and can lead to a new class of frequency comb sources that may stimulate novel applications by enabling straightforward access to elusive spectral regions, such as the midinfrared.

The ring-opening channel and the influence of Rydberg states on the excited state dynamics of furan and its derivatives.

One important relaxation pathway for photo-excited five-membered heterocyclic organic molecules is ring-opening via a dissociative πσ* state. In this study, we investigate the influence of this pathway in furan and several hydrogenated and methylated derivatives by combining time-resolved photoelectron spectroscopy with time-dependent density functional theory and coupled cluster calculations. We find strong experimental evidence that the ring-opening channel is the major relaxation channel in furan, 2,3-dihydrofuran, and 2-methylfuran (2-MF). In 2,5-dimethylfuran (25-DMF), however, we observe that the molecules relax either via a π3s Rydberg state or through a direct return to the ground state by undergoing ring-puckering motions. From the supporting calculations, for 2-MF and 25-DMF, we predict that there is strong mixing between the πσ* state and the π3s Rydberg state along the ring opening pathway. However, in 25-DMF, no crossing between the πσ*/π3s state and the initially excited ππ* state can be found along the ring opening coordinate, effectively blocking this channel.

Proposed Spontaneous Generation of Magnetic Fields by Curved Layers of a Chiral Superconductor.

We demonstrate that two-dimensional chiral superconductors on curved surfaces spontaneously develop magnetic flux. This geometric Meissner effect provides an unequivocal signature of chiral superconductivity, which could be observed in layered materials under stress. We also employ the effect to explain some puzzling questions related to the location of zero-energy Majorana modes.

The effects of person-centered or other supportive interventions in older women with osteoporotic vertebral compression fractures-a systematic review of the literature.

Vertebral compression fracture (VCF) is a common fragility fracture and the starting point of a lasting, painful, disabling condition. The aim was to summarize evidence of person-centered/non-medical interventions supporting women with VCF. Results show small numbers of studies with only probable effect on function, pain, QoL, fear of falling, and psychological symptoms. The vertebral compression fracture (VCF) caused by osteoporosis is the third most common fragility fracture worldwide. Previously, it was believed that the pain caused by VCF was self-subsiding within weeks or a few months post-fracture. However, this positive prognosis has been refuted by studies showing that, for the great majority of patients, the VCF was the starting point of a long-lasting, severely painful, and disabling condition. The low number of studies focusing on the experience of the natural course of VCF, and what support is available and how it is perceived by those affected, calls for further investigation. Strengthening older patients' sense of security and increasing confidence in their own abilities are of great importance for successful rehabilitation following VCF. More research is needed to identify resources, possibilities, and strategies that can assist older patients to reach their goals to improve well-being. The purpose of this systematic review was to identify and summarize the current evidence of person-centered or other structured non-medical/non-surgical interventions supporting older women after experiencing an osteoporotic VCF. A systematic literature search was conducted on the MeSH terms encompassing osteoporosis and vertebral compression fractures in the PubMed-MEDLINE and Cumulative Index for Nursing and Allied Health Literature (CINAHL) databases during March through June 2015. The initial search identified 8789 articles, but only seven articles (six randomized controlled trials and one observational study with a control group) met the inclusion criteria. It became evident from the current study that the availability of evidence on the effects of non-medical interventions aiming to support older women with VCF is limited, to say the least. The trials included in this review have few limitations and were mainly considered to be of moderate quality. This systematic literature review suggests that non-medical interventions aiming to support older women with VCF might decrease levels of pain and use of analgesic as well as promote improved physical mobility and function. These interventions would probably result in an improved difference in experiences of fear of falling and perceived psychological symptoms, but would only slightly improve quality of life. However, given the nature of the seven studies, potential biases in patient selection, issues around precision with small cohorts, and failure to control for confounders, makes it difficult to draw a definitive conclusion about the significant effects of non-medical interventions. Incurring a VCF is a complex and diverse event, necessitating equally complex interventions to identify new ways forward. However, to date, interventions struggle with a risk of selection bias in that only the needs of the healthiest of the population are addressed and the voices of the remaining majority of the people affected by VCF are unheard.

Multiple four-wave mixing and Kerr combs in a bichromatically pumped nonlinear fiber ring cavity.

We report numerical and experimental studies of multiple four-wave mixing processes emerging from dual-frequency pumping of a passive nonlinear fiber ring cavity. We observe the formation of a periodic train of nearly background-free soliton pulses associated with Kerr frequency combs. The generation of resonant dispersive waves is also reported.

Walk-Off-Induced Modulation Instability, Temporal Pattern Formation, and Frequency Comb Generation in Cavity-Enhanced Second-Harmonic Generation.

We derive a time-domain mean-field equation to model the full temporal and spectral dynamics of light in singly resonant cavity-enhanced second-harmonic generation systems. We show that the temporal walk-off between the fundamental and the second-harmonic fields plays a decisive role under realistic conditions, giving rise to rich, previously unidentified nonlinear behavior. Through linear stability analysis and numerical simulations, we discover a new kind of quadratic modulation instability which leads to the formation of optical frequency combs and associated time-domain dissipative structures. Our numerical simulations show excellent agreement with recent experimental observations of frequency combs in quadratic nonlinear media [Phys. Rev. A 91, 063839 (2015)]. Thus, in addition to unveiling a new, experimentally accessible regime of nonlinear dynamics, our work enables predictive modeling of frequency comb generation in cavity-enhanced second-harmonic generation systems. We expect our findings to have wide impact on the study of temporal and spectral dynamics in a diverse range of dispersive, quadratically nonlinear resonators.

A painful, never ending story: older women's experiences of living with an osteoporotic vertebral compression fracture.

UNLABELLED: Vertebral compression fractures (VCF) cause pain and decreased physical ability, with no known well-established treatment. The aim of this study was to illuminate the experience of living with a VCF. The results show that fear and concerns are a major part of daily life. The women's initial contact with health-care providers should focus on making them feel acknowledged by offering person-centered and tailored support. INTRODUCTION: In the past decade, osteoporotic-related fractures have become an increasingly common and costly public health problem worldwide. Vertebral compression fracture (VCF) is the second most common osteoporotic fracture, and patients with VCF describe an abrupt descent into disability, with a subsequent desire to regain independence in everyday life; however, little is known of their situation. The aim of this study was to illuminate the lived experience of women with an osteoporotic VCF. METHODS: Ten women were interviewed during 2012-2013, starting with an open-ended question: could you tell me what it is like to live with a vertebral compression fracture? The verbatim transcribed interviews were analyzed using a phenomenological hermeneutical approach. RESULTS: The narrative provided descriptions of living in turmoil and chaos, unable to find stability in their life with little improvement regarding pain and physical function. Shifts from periods of constant pain to periods of fear of constant pain created a loss of confidence and an increased sense of confinement. The structural analysis revealed fear and concerns as the most prominent experience building on five themes: struggling to understand a deceiving body, breakthrough pain fueling fear, fearing a trajectory into isolation, concerns of dependency, and fearing an uncertain future. CONCLUSIONS: Until researchers find a successful prevention or medical/surgical treatment for osteoporotic VCFs, health-care providers and society abandon these women to remain in a painful and never ending story.

Influence of Alkoxy Groups on the Photoinduced Dynamics of Organic Molecules Exemplified on Alkyl Vinyl Ethers.

A series of different alkyl vinyl ethers is investigated to decipher the possible reaction channels upon photoexcitation to the π3s-Rydberg and the ππ*-valence state at 200 nm using time-resolved photoelectron spectroscopy and on-the-fly time-dependent density functional theory dynamics simulations. The results indicate two possible relaxation pathways: (1) a radiationless decay through the ππ*-state back to the ground state via torsion of the C═C double bond, in accordance with the dynamics found in ethylene; and (2) a fast dissociation of the C-O bond between the alkyl and the vinoxy group in the πσ*-state. The latter state can be accessed only after excitation to the π3s-Rydberg state (quantum yield of ∼50% according to the dynamics simulations). Additionally, the excited state barrier leading to formation of a vinyl radical was found to be too high to be crossed. These results indicate that the dynamics of ethers crucially depend on the excitation wavelength and that the πσ*-state constitutes an important competitive reaction channel that leads to dissociation of the molecules.

Topological aspects of π phase winding junctions in superconducting wires.

We theoretically investigate Josephson junctions with a phase shift of π in various proximity induced one-dimensional superconductor models. One of the salient experimental signatures of topological superconductors, namely the fractionalized 4π periodic Josephson effect, is closely related to the occurrence of a characteristic zero energy bound state in such junctions. We make a detailed analysis of a more general type of π-junctions coined 'phase winding junctions' where the phase of the order parameter rotates by an angle π while its absolute value is kept finite. Such junctions have different properties, also from a topological viewpoint, and there are no protected zero energy modes. We compare the phenomenology of such junctions in topological (p-wave) and trivial (s-wave) superconducting wires, and briefly discuss possible experimental probes. Furthermore, we propose a topological field theory that gives a minimal description of a wire with defects corresponding to π-junctions. This effective theory is a one-dimensional version of similar theories describing Majorana bound states in half-vortices of two-dimensional topological superconductors.

Strong and parallel salinity-induced phenotypic plasticity in one generation of threespine stickleback.

Phenotypic plasticity is a major factor contributing to variation of organisms in nature, yet its evolutionary significance is insufficiently understood. One example system where plasticity might have played an important role in an adaptive radiation is the threespine stickleback (Gasterosteus aculeatus), a fish that has diversified after invading freshwater lakes repeatedly from the marine habitat. The parallel phenotypic changes that occurred in this radiation were extremely rapid. This study evaluates phenotypic plasticity in stickleback body shape in response to salinity in fish stemming from a wild freshwater population. Using a split-clutch design, we detected surprisingly large phenotypically plastic changes in body shape after one generation. Fish raised in salt water developed shallower bodies and longer jaws, and these changes were consistent and parallel across families. Although this work highlights the effect of phenotypic plasticity, we also find indications that constraints may play a role in biasing the direction of possible phenotypic change. The slopes of the allometric relationship of individual linear traits did not change across treatments, indicating that plastic change does not affect the covariation of traits with overall size. We conclude that stickleback have a large capacity for plastic phenotypic change in response to salinity and that plasticity and evolutionary constraints have likely contributed to the phenotypic diversification of these fish.

Integrability and conservation laws for the nonlinear evolution equations of partially coherent waves in noninstantaneous Kerr media.

It is shown that the evolution equations describing partially coherent wave propagation in noninstantaneous Kerr media are integrable and have an infinite number of invariants. A recursion relation for generating these invariants is presented, and it is demonstrated how to express them in the coherent density, self-consistent multimode, mutual coherence, and Wigner formalisms.

Generalized dressing method for nonlinear evolution equations describing partially coherent wave propagation in noninstantaneous Kerr media.

A generalized dressing method is presented for integration of the nonlinear evolution equation of the coherent density function describing partially coherent wave propagation in a noninstantaneous Kerr media. As an example an exact, partially coherent multisource N-soliton solution is derived. It is also demonstrated how this method is applicable for construction of solutions to the equivalent coupled system of nonlinear Schrödinger equations of the self-consistent multimode theory.

Reconstructing nonlinearities with intermodulation spectroscopy.

We describe a method of analysis which allows for reconstructing the nonlinear disturbance of a high Q harmonic oscillator. When the oscillator is driven with two or more frequencies, the nonlinearity causes intermodulation of the drives, resulting in a complicated spectral response. Analysis of this spectrum allows one to approximate the nonlinearity. The method, which is generally applicable to measurements based on resonant detection, increases the information content of the measurement without requiring a large detection bandwidth, and optimally uses the enhanced sensitivity near resonance to extract information and minimize error due to detector noise.

A photoelectron and double photoionization study of the valence electronic structure of 1,4-bromofluorobenzene.

Conventional photoelectron and time-of-flight photoelectron-photoelectron coincidence (TOF-PEPECO) spectra have been measured for the outer valence region of the 1,4-bromofluorobenzene molecule. The photoelectron spectra were recorded using HeI alpha radiation from a resonance source, and the TOF-PEPECO spectra were recorded using HeII alpha radiation from a pulsed resonance source. The former provide energies of the cationic states and the latter of the dicationic states. The spectra are adequately interpreted with the aid of accurate Green's function calculations, showing very significant correlation effects. The lowest double ionization energy is found at 23.45 eV associated with the (4b(1))(-2)X (1)A(1) dicationic state.

Conformal field theory approach to Abelian and non-Abelian quantum Hall quasielectrons.

The quasiparticles in quantum Hall liquids carry fractional charge and obey fractional quantum statistics. Of particular recent interest are those with non-Abelian statistics, since their braiding properties could, in principle, be used for robust coding of quantum information. There is already a good theoretical understanding of quasiholes in both Abelian and non-Abelian quantum Hall states. Here we develop conformal field theory methods that allow for an equally precise description of quasielectrons and explicitly construct two- and four-quasielectron excitations of the non-Abelian Moore-Read state.

A unifying hypothesis on the development of type 1 diabetes and celiac disease: gluten consumption may be a shared causative factor.

This paper presents a hypothesis of the aetiology of the increasing incidence of type 1 diabetes (T1D). This together with the global increased incidence of celiac disease (CD) and that these increases cannot be explained by genetic factors suggest a common environmental factor for these two diseases. Even though enterovirus (EV) infections are believed to trigger T1D and gluten is the trigger of CD, the increasing intake of gluten containing products all over the world could be the trigger for both diseases directly and indirectly. It has been shown that the duration of exposure to gluten is related to the prevalence of T1D. It has also been shown that T1D patients at onset have an inflammatory reaction in the gut. Hence, early diagnose of CD followed by elimination of dietary gluten will lead to a decreased incidence of T1D.