Continuum Of Modes Research Articles

Activin A Suppresses Osteoblast Mineralization Capacity by Altering Extracellular Matrix (ECM) Composition and Impairing Matrix Vesicle (MV) Production

During bone formation, osteoblasts deposit an extracellular matrix (ECM) that is mineralized via a process involving production and secretion of highly specialized matrix vesicles (MVs). Activin A, a transforming growth factor-β (TGF-β) superfamily member, was previously shown to have inhibitory effects in human bone formation models through unclear mechanisms. We investigated these mechanisms elicited by activin A during in vitro osteogenic differentiation of human mesenchymal stem cells (hMSC). Activin A inhibition of ECM mineralization coincided with a strong decline in alkaline phosphatase (ALP(1)) activity in extracellular compartments, ECM and matrix vesicles. SILAC-based quantitative proteomics disclosed intricate protein composition alterations in the activin A ECM, including changed expression of collagen XII, osteonectin and several cytoskeleton-binding proteins. Moreover, in activin A osteoblasts matrix vesicle production was deficient containing very low expression of annexin proteins. ECM enhanced human mesenchymal stem cell osteogenic development and mineralization. This osteogenic enhancement was significantly decreased when human mesenchymal stem cells were cultured on ECM produced under activin A treatment. These findings demonstrate that activin A targets the ECM maturation phase of osteoblast differentiation resulting ultimately in the inhibition of mineralization. ECM proteins modulated by activin A are not only determinant for bone mineralization but also possess osteoinductive properties that are relevant for bone tissue regeneration.

Energy exchange and scattering loss within a two-way coupled-mode formulation

The loss of energy due to propagation in an ocean environment arises from several possible processes. In a two-way coupled-mode description scattering effects from a rough bottom Pekeris waveguide can be isolated by excluding bulk attenuation, and intermodal energy exchange can be examined. The range- and frequency-dependent interaction of a single trapped mode exchanging energy with multiple continuum modes is identified within this framework. The goal of the analysis is two-fold. First, it provides insight into additional loss mechanisms that can be incorporated into current local mode models (c.f. Koch and Stotts, A Derivation of Energy Loss via Coupled Modes, 165th Meeting of the Acoustical Society of America, June 2–7, 2013). Second, a comparison can be made to previous descriptions of additional attenuation, such as Kirchhoff scattering loss. Varying the bottom roughness permits tests of the applicability of the Born approximation.

Manifestation of phonons in the optical spectra of pseudo Jahn-Teller systems

The system under consideration is a molecule or an impurity center in a crystal with a two-fold quasi-degenerate electronic state (pseudo Jahn-Teller system) in strong interaction with one main mode and in weak interaction with continuum of secondary modes of phonons. This system exhibits strong non-adiabatic couplings which have been demonstrated to be detectable in absorption and Raman excitation spectra. By choosing an appropriate axis of polarization the non-adiabatic transitions become directly observable.

Super-Planckian near-field thermal emission with phonon-polaritonic hyperbolic metamaterials

We study super-Planckian near-field heat exchanges for multilayer hyperbolic metamaterials using exact scattering-matrix (S-matrix) calculations. We investigate heat exchanges between two multilayer hyperbolic metamaterial structures. We show that the super-Planckian emission of such metamaterials can either come from the presence of surface phonon-polariton modes or from a continuum of hyperbolic modes depending on the choice of composite materials as well as the structural configuration.

Nonadiabaticity in a Jahn-Teller system probed by absorption and resonance Raman scattering

A theory of absorption and resonance Raman scattering of impurity centers in crystals with E⊗e-type Jahn-Teller effect in the excited state is presented. The vibronic interaction with non-totally symmetric local or pseudolocal modes and with a continuum of bath modes (phonons) is considered. A number of specific quantum effects, such as the nonadiabaticity-induced enhancement of the Raman scattering at high-energy excitation, the size effect of the final state, the interference of different channels of scattering, the Fermi resonances in the conical intersection, and others, were shown to become apparent in the calculated spectra. The vibronic interaction with phonons essentially determines the structure of the spectra.

Visitors and Residents: mapping student attitudes to academic use of social networks

The Visitors and Residents model of internet use suggests a continuum of modes of engagement with the online world, ranging from tool use to social spaces. In this paper, we examine evidence derived from a large cohort of students to assess whether this idea can be validated by experimental evidence. We find statistically significant differences between individuals displaying ‘Visitor’ or ‘Resident’ attitudes, suggesting that the Visitors and Residents model is a useful typology for approaching and understanding online behaviour. From our limited sample, we have been able to produce evidence that the Visitors and Residents labels are statistically robust. This demonstrates that the Visitors and Residents approach provides a valuable framework for those considering the use of social tools in educational contexts.

Femtosecond laser writing of optical edge filters in fused silica optical waveguides

The positional alignment of femtosecond laser written Bragg grating waveguides within standard and coreless optical fiber has been exploited to vary symmetry and open strong optical coupling to a high density of asymmetric cladding modes. This coupling was further intensified with tight focusing of the laser pulses through an oil-immersion lens to control mode size against an asymmetric refractive index profile. By extending this Bragg grating waveguide writing into bulk fused silica glass, strong coupling to a continuum of radiation-like modes facilitated a significant broadening to over hundreds of nanometers bandwidth that blended into the narrow Bragg resonance to form into a strongly isolating (43 dB) optical edge filter. This Bragg resonance defined exceptionally steep edge slopes of 136 dB/nm and 185 dB/nm for unpolarized and linearly polarized light, respectively, that were tunable through the 1450 nm to 1550 nm telecommunication band.

Metamaterial inspired terahertz devices: from ultra-sensitive sensing to near field manipulation

We present a review of terahertz plasmonic metamaterial devices that have functionalities and applications ranging from sensing, enhanced electromagnetic fields, and near field manipulation. Metamaterials allow the properties of light propagation to be manipulated at will by using a combination of appropriately designed geometry and suitable materials at the unit cell level. In this review, we first discuss the sensing aspect of a planar plasmonic metamaterial and how to overcome its limitations. Conventional symmetric metamaterials are limited by their low Q factor, thus we probed the symmetry broken plasmonic metamaterial structures in which the interference between a broad continuum mode and a narrow localized mode leads to the excitation of the sharp Fano resonances. We also discuss the near field mediated excitation of dark plasmonic modes in metamaterials that is caused by a strong coupling from the bright mode resonator. The near field coupling between the dark and bright mode resonances leads to classical analogue of electromagnetically induced transparency in plasmonic systems. Finally, we discuss active switching in terahertz metamaterials based on high temperature superconductors that holds the promise of reducing the resistive losses in these systems, though it fails to suppress the radiation loss in plasmonic metamaterial at terahertz frequencies.

Gene Expression Profiles Document That Recently- and Previously-Divided CLL Fractions Represent a Continuum but Suggest Differing Modes of Activation for These Fractions in U-CLL and M-CLL

AbstractAbstract 317By using reciprocal densities of surface membrane CXCR4 and CD5, chronic lymphocytic leukemia (CLL) B cells can be divided into 3 fractions indicating time since last division (proliferative, intermediate, and resting). It has been suggested that cells in these fractions represent a continuum from resting to intermediate to proliferative. In this study, we made intraclonal gene expression profile (GEP) comparisons of these fractions from 17 CLL patients to try to confirm this notion and interclonal comparisons between U-CLL and M-CLL patients to determine if pathways involved in the actions of these fractions differed between patient subgroups.PBMCs from 8 U-CLL and 9 M-CLL patients were sorted into 3 fractions (CD19+CD3−CD5hiCXCR4lo, PROLIF), (CD19+CD3−CD5intCXCR4int, INTERM), and (CD19+CD3−CD5loCXCR4hi, REST); RNA was purified from each, and gene expression microarrays using Illumina HumanHT12 beadchips performed. To determine differentially expressed genes in intraclonal comparisons, expression value ratios for fractions from each patient were computed, log-transformed, and Student t-test performed using R (www.r-project.org); for interclonal comparisons, raw GEP data between subpopulations were compared: U-PROLIF and M-PROLIF, and U-REST and M-REST. Sets of significant genes (≥1.5 fold change and P<0.01) were analyzed using Ingenuity Pathway Analysis (IPA) and Gene Set Enrichment Analysis (GSEA).Upon plotting intraclonal average log ratios of PROLIF/INTERM vs INTERM/REST, it was clear that gene expression levels changed in the same direction, i.e. PROLIF>INTERM>REST, or PROLIF<INTERM<REST, consistent with a continuum between the 3 fractions. Within this pattern, 36 genes were significant for both plotted ratios. Of these, 29 were overexpressed, along with CD5; CD68, ITGAX, CCND2, CRIP1 and LGALS1 were the highest. Functional analysis using IPA showed these genes to be related to NFkB signaling and cell trafficking. Seven genes (ADARB1, BACH2, CNTNAP2, HRK, RHPN2, PRPML, and RXPA) were significantly downregulated, along with CXCR4.Next we characterized GEP differences between the PROLIF and REST fractions, identifying 390 genes up-regulated in PROLIF and 244 in REST. The top 5 upregulated PROLIF genes were CD68, LY96, ITGAX, CCND2 and CRIP1, and the top 5 REST genes were BACH2, CXCR4, ADARB1, RHPN2 and HRK. Functionally, the upregulated PROLIF genes were related to BCR signaling, cytokines (IFNa, IL12), NFkB, and Akt, whereas the upregulated REST genes related to BCL2, cell death and cell movement. By GSEA, 813/881 gene sets, defined by expression neighborhoods centered on cancer associated genes, were upregulated in the PROLIF with 436 gene sets significant at a false discovery rate (FDR) <10%; 206 sets were significantly enriched with p value <0.01. For the REST, 68/881 gene sets were upregulated, with none significant even at FDR <25%.Finally, we examined PROLIF and REST fractions from U-CLL vs M-CLL patients. In this interclonal analysis, 93 genes were significantly different between U-PROLIF and M-PROLIF. The top 5 in U-PROLIF were MSI2, TGFBR3, TP53I3, RGCC and IGSF3, and the top 5 in M-PROLIF were MTSS1, BACE2, BRI3BP, AP3B1 and UBE2G2. Similarly, there were 125 genes that were significantly different between U-REST and M-REST. The top 5 in U-REST were DUSP26, CLEC2B, MDK, and EGR2 and in M-REST were NAPSA, RAB24, TARDBP, KCNN4 and ADD3. Interestingly, U-PROLIF and M-PROLIF differed in pathway assignments, with upregulated genes in U-PROLIF contributing to cell signaling and activation, particularly implicating Akt, ERK and P38MAPK.The intraclonal gene GEP analysis on these 3 fractions confirms that CLL clones contain a spectrum of cells that transition in a sequential manner from PROLIF to INTERM to REST fractions. Functional analyses show that genes upregulated in PROLIF correlate with cell signaling and proliferation, while genes upregulated in REST relate to cell death. Thus the PROLIF fraction is enriched in recently divided cells that likely exit from lymphoid tissue and the REST in older, less vital cells that either traffic to lymphoid tissue or die. The interclonal analysis implies that the stimuli and/or the responses of cells in the PROLIF and REST fractions differ between U-CLL and M-CLL. This last novel finding suggests either distinct cells of origin or distinct activation pathways for the IGHV-defined CLL subsets. Disclosures:Barrientos:gilead and pharmacyclics research funding: Research Funding.

Conic hyperspectral dispersion mapping applied to semiconductor plasmonics

The surface plasmon resonance tracking over metal surfaces is a well-established, commercially available, biochemical quantification tool primarily applied in research. The utilization of such a tool is, however, constrained to highly specialized industries, capable of justifying the human and instrumental resource investments required by the characterization method. We have proposed to expand the field of application of this biosensing approach by redesigning this method through the integration and miniaturization within a semiconductor platform. Uncollimated and broadband emission from a light-emitting semiconductor is employed to couple a continuum of surface plasmon modes over a metal–dielectric architecture interfaced with a GaAs–AlGaAs substrate. A tensor version of rigorous coupled wave theory is employed to optimize the various fabrication specifications and to predict the light scatterings over a wide range of variables. We then present a hyperspectral characterization microscope capable of directly mapping the dispersion relation of scattered light, including diffracted surface plasmons, as an intensity distribution versus photon energy and surface wavevectors. Measurements carried out in a buffered solution demonstrate the accurate description of the uncollimated and broadband surface plasmon states. Finally, we introduce a simplified method of dispersion mapping, in which quasi-conic cross-sections of the light's scattering can be acquired directly, thus monitoring surficial responses in as fast as 1.2 s. This is over 300 times faster than required by implementing full dispersion mapping. While compromising on the volume of collected information, this method, combined with the solid-state integration of the platform, shows great promise for the fast detection of biochemical agents. Researchers have miniaturized surface plasmon resonance experiments by using microchips embedded with gallium arsenide ‘quantum wells’. One of the best ways to track biochemical agents is through surface plasmon resonance spectroscopy, a technique that uses vibrations from a thin metal layer to detect specific molecular adsorption events. However, observing surface plasmons for biosensing traditionally requires the use of large, precisely tuned light sources. The scheme developed by Dubowski and co-workers employs hyperspectral imaging—a means of measuring data from hundreds of different spectral bands—to record how the broadband light of quantum well nanostructures scatters after striking a metal film. Advanced algorithms then pick out surface plasmons from the light-scattering data and enable near real-time analysis. Solid-state integration and pre-analysed output make this device ideal for future commercial ventures that could go beyond the application of surface plasmon resonance for biosensing.

Light–matter interaction in free space

We review recent experimental advances in the field of efficient coupling of single atoms and light in free space. Furthermore, a comparison of efficient free space coupling and strong coupling in cavity quantum electrodynamics (QED) is given. Free space coupling does not allow for observing oscillatory exchange between the light field and the atom which is the characteristic feature of strong coupling in cavity QED. Like cavity QED, free space QED does, however, offer full switching of the light field, a 180° phase shift conditional on the presence of a single atom as well as 100% absorption probability of a single photon by a single atom. Furthermore, free space cavity QED comprises the interaction with a continuum of modes.

Measuring higher-order modes in a low-loss, hollow-core, photonic-bandgap fiber

We perform detailed measurements of the higher-order-mode content of a low-loss, hollow-core, photonic-bandgap fiber. Mode content is characterized using Spatially and Spectrally resolved (S2) imaging, revealing a variety of phenomena. Discrete mode scattering to core-guided modes are measured at small relative group-delays. At large group delays a continuum of surface modes and core-guided modes can be observed. The LP11 mode is observed to split into four different group delays with different orientations, with the relative orientations preserved as the mode propagates through the fiber. Cutback measurements allow for quantification of the loss of different individual modes. The behavior of the modes in the low loss region of the fiber is compared to that in a high loss region of the fiber. Finally, a new measurement technique is introduced, the sliding-window Fourier transform of high-resolution transmission spectra of hollow-core fibers, which displays the dependence of HOM content on both wavelength and group delay. This measurement is used to illustrate the HOM content as function of coil diameter.

Graphene-based polaritonic crystal

It is shown that monolayer graphene deposited on a spatially periodic gate behaves as a polaritonic crystal. Its band structure depending on the applied gate voltage is studied. The scattering of electromagnetic radiation from such a crystal is presented calculated and its spectral dependence is analyzed in terms of Fano-type resonances between the reflected continuum and plasmon-polariton modes forming narrow bands.

Comment on “Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks” [Phys. Plasmas 18, 092103 (2011)

It is shown that some of the main results of the recent paper by Lakhin and Ilgisonis [Phys. Plasmas 18, 092103 (2011)], viz. the derivation of the equations for the continuous spectra of poloidally and toroidally rotating plasmas and their special solution for large aspect ratio tokamaks with large parallel flows were obtained before by Goedbloed, Beliën, van der Holst, and Keppens [Phys. Plasmas 11, 28 (2004)]. A further rearrangement of the system of equations for the coupled Alfvén and slow continuous spectra clearly exhibits: (a) coupling through a single tangential derivative, which is a generalization of the geodesic curvature; (b) the “transonic” transitions of the equilibrium, which need to be carefully examined in order to avoid entering hyperbolic flow regimes where the stability formalism breaks down. A critical discussion is devoted to the implications of this failure, which is generally missed in the tokamak literature, possibly as a result of the wide-spread use of the sonic Mach number of gas dynamics, which is an irrelevant and misleading parameter in “transonic” magnetohydrodynamics. Once this obstacle in understanding is removed, further application of the theory of trans-slow Alfvén continuum instabilities to both tokamaks, with possible implications for the L-H transition, and astrophysical objects like “fat” accretion disks, with a possible new route to magnetohydrodynamic turbulence, becomes feasible.

Response to “Comment on ‘Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks’ ” [Phys. Plasmas 19, 064701 (2012)

The equations for the continuous spectra derived in our paper [V. P. Lakhin and V. I. Ilgisonis, Phys. Plasmas 18, 092103 (2011)] can be reduced to the matrix form used by Goedbloed et al. [Phys. Plasmas 11, 28 (2004)]. It is shown that the assumptions made in our paper provide the elliptic flow regime and guarantee the existence of plasma equilibrium with nested magnetic surfaces of circular cross-section. The new results on magnetohydrodynamic instabilities of such tokamak equilibria obtained in our paper but absent in the paper by Goedbloed et al. are emphasized.

Coherent cavity networks with complete connectivity

When cavity photons couple to an optical fiber with a continuum of modes, they usually leak out within a finite amount of time. However, if the fiber is about 1 m long and linked to a mirror, photons bounce back and forth within the fiber on a much faster time scale. As a result, dynamical decoupling prevents the cavity photons from entering the fiber. In this paper, we use the simultaneous dynamical decoupling of a large number of distant cavities from the fiber modes of linear optics networks to mediate effective cavity–cavity interactions in a large variety of configurations. Coherent cavity networks with complete connectivity can be created with potential applications in quantum computing and in the simulation of the complex interaction Hamiltonians of biological systems.

Relevance of the light line in planar photonic crystal waveguides with weak vertical confinement

The concept of the so-called light line is a useful tool to distinguish between guided and non-guided modes in dielectric slab waveguides. Also for more complicated structures with 2D mode confinement, the light lines can often be used to divide a dispersion diagram into a region of a non-guided continuum of modes, a region of discrete guided modes and a forbidden region, where no propagating modes can exist. However, whether or not the light line is a concept of practical relevance depends on the geometry of the structure. This fact is sometimes ignored. For instance, in the literature on photonic crystal waveguides, it is often argued that substrate-type photonic crystal waveguides with a weak vertical confinement are inherently lossy, since the entire bandgap including the line defect modes is typically located above the light line of the substrate. The purpose of this article is to illustrate that this argument is inaccurate and to provide guidelines on how an improved light line concept can be constructed.

Non-Markovian autoresonant dynamics of tunneling from discrete to continuum modes

We study the autoresonant dynamics of a discrete level coupled to a continuum, and show that passing adiabatically through a linear resonance, above a well-defined threshold, yields a transition to nonlinear phase locking and linear non-Markovian decay to the continuum. This process results in broadening of the population of the continuum modes beyond its natural linewidth. This concept can be employed to alter spontaneous emission, where driving an atom into phase locking with continuum modes will yield the emission of short pulses.

Determination of elemental composition of volatile organic compounds from Chinese rose oil by spectral accuracy and mass accuracy

Elemental composition determination of volatile organic compounds through high mass accuracy and isotope pattern matching could not be routinely achieved with a unit-mass resolution mass spectrometer until the recent development of the comprehensive instrument line-shape calibration technology. Through this unique technology, both m/z values and mass spectral peak shapes are calibrated simultaneously. Of fundamental importance is that calibrated mass spectra have symmetric and mathematically known peak shapes, which makes it possible to deconvolute overlapped monoisotopes and their (13)C-isotope peaks and achieve accurate mass measurements. The key experimental requirements for the measurements are to acquire true raw data in a profile or continuum mode with the acquisition threshold set to zero. A total of 13 ions from Chinese rose oil were analyzed with internal calibration. Most of the ions produced high mass accuracy of better than 5 mDa and high spectral accuracy of better than 99%. These results allow five tested ions to be identified with unique elemental compositions and the other eight ions to be determined as a top match from multiple candidates based on spectral accuracy. One of them, a coeluted component (Nerol) with m/z 154, could not be identified by conventional GC/MS (gas chromatography/mass spectrometry) and library search. Such effective determination for elemental compositions of the volatile organic compounds with a unit-mass resolution quadrupole system is obviously attributed to the significant improvement of mass accuracy. More importantly, high spectral accuracy available through the instrument line-shape calibration enables highly accurate isotope pattern recognition for unknown identification.

Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks

A theory for localized low-frequency ideal magnetohydrodynamical (MHD) modes in axisymmetric toroidal systems is generalized to take into account both toroidal and poloidal equilibrium plasma flows. The general set of equations describing the coupling of shear Alfvén and slow (sound) modes and defining the continuous spectrum of rotating plasmas in axisymmetric toroidal systems is derived. The equations are applied to study the continuous spectra in large aspect ratio tokamaks. The unstable continuous modes in the case of predominantly poloidal plasma rotation with the angular velocity exceeding the sound frequency are found. Their stabilization by the shear Alfvén coupling effect is studied.