Critical States Embedded in the Continuum

We introduce a class of critical states which are embedded in the continuum (CSC) of one-dimensional optical waveguide array with one non-Hermitian defect. These states are at the verge of being fractal and have real propagation constant. They emerge at a phase transition which is driven by the imaginary refractive index of the defect waveguide and it is accompanied by a mode segregation which reveals analogies with the Dicke super -radiance. Below this point the states are extended while above they evolve to exponentially localized modes. An addition of a background gain or loss can turn these localized states to bound states in the continuum.Comment: 4.5 pages, 3 figures, 1 page of supplementary material including one figur

Multiband Bandstop Filter using an I-Stub-Loaded Meandered Defected Microstrip Structure

This paper presents a compact multiband bandstop filter (BSF) that utilizes an I-stub embedded within a meandered defected microstrip structure (MDMS). The proposed design for obtaining a single stopband is analyzed by using a transmission line network model. On the basis of the single stopband structure, we designed and fabricated a dual- and tri-band bandstop filters operating at 2.5/6.78 GHz and 1.98/5.60/7.78 GHz, respectively, thereby exploring the concept of generating as many stopbands by simply adding the same number of I-stubs. The proposed filter also features the possibility of tuning the resonant frequencies by varying the width of the I-stubs

Calibration and Irradiation Study of the BGO Background Monitor for the BEAST II Experiment

Beam commissioning of the SuperKEKB collider began in 2016. The Beam Exorcism for A STable experiment II (BEAST II) project is particularly designed to measure the beam backgrounds around the interaction point of the SuperKEKB collider for the Belle II experiment. We develop a system using bismuth germanium oxide (BGO) crystals with optical fibers connecting to a multianode photomultiplier tube (MAPMT) and a field-programmable gate array (FPGA) embedded readout board for monitoring the real-time beam backgrounds in BEAST II. The overall radiation sensitivity of this system is estimated to be $(2.20\pm0.26)\times10^{-12}$ Gy/ADU (analog-to-digital unit) with the standard 10 m fibers for transmission and the MAPMT operating at 700 V. Our $\gamma$-ray irradiation study of the BGO system shows that the exposure of BGO crystals to $^{60}$Co $\gamma$-ray doses of 1 krad has led to immediate light output reductions of 25--40%, and the light outputs further drop by 30--45% after the crystals receive doses of 2--4 krad. Our findings agree with those of the previous studies on the radiation hard (RH) BGO crystals grown by the low thermal gradient Czochralski (LTG Cz) technology. The absolute dose from the BGO system is also consistent with the simulation, and is estimated to be about 1.18 times the equivalent dose. These results prove that the BGO system is able to monitor the background dose rate in real time under extreme high radiation conditions. This study concludes that the BGO system is reliable for the beam background study in BEAST II

Illustrating a new global-scale approach to estimating potential reduction in fish species richness due to flow alteration

Changes in river discharge due to human activities and climate change would affect the sustainability of freshwater ecosystems. To globally assess how changes in river discharge will affect the future status of freshwater ecosystems, global-scale hydrological simulations need to be connected with a model to estimate the durability of freshwater ecosystems. However, the development of this specific modelling combination for the global scale is still in its infancy. In this study, two statistical methods are introduced to link flow regimes to fish species richness (FSR): one is based on a linear relationship between FSR and mean river discharge (hereafter, FSR-MAD method), and the other is based on a multi-linear relationship between FSR and ecologically relevant flow indices involving several other flow characteristics and mean river discharge (FSR-FLVAR method). The FSR-MAD method has been used previously in global simulation studies. The FSR-FLVAR method is newly introduced here. These statistical methods for estimating FSR were combined with a set of global river discharge simulations to evaluate the potential impact of climate-change-induced flow alterations on FSR changes. Generally, future reductions in FSR with the FSR-FLVAR method are greater and much more scattered than with the FSR-MAD method. In arid regions, both methods indicate reductions in FSR because mean discharge is projected to decrease from past to future, although the magnitude of reductions in FSR is different between the two methods. In contrast, in heavy-snow regions a large reduction in FSR is shown by the FSR-FLVAR method due to increases in the frequency of low and high flows. Although further research is clearly needed to conclude which method is more appropriate, this study demonstrates that the FSR-FLVAR method could produce considerably different results when assessing the global role of flow alterations in changing freshwater ecosystems

Superhalogen properties of CumCln clusters: Theory and experiment

Using a combination of density functional theory and anion photoelectron spectroscopy experiment, we have studied the structure and electronic properties of CuCl n − (n = 1–5) and Cu2Cl n − (n = 2–5) clusters. Prominent peaks in the mass spectrum of these clusters occurring at n = 2, 3, and 4 in CuCl n − and at n = 3, 4, and 5 in Cu2Cl n − are shown to be associated with the large electron affinities of their neutral clusters that far exceed the value of Cl. While CuCl n(n ≥ 2) clusters are conventional superhalogens with a metal atom at the core surrounded by halogen atoms, Cu2Cl n (n ≥ 3) clusters are also superhalogens but with (CuCl)2 forming the core. The good agreement between our calculated and measured electron affinities and vertical detachment energies confirm not only the calculated geometries of these superhalogens but also our interpretation of their electronic structure and relative stability

Distinct cortical and subcortical structural alterations mirroring daytime‐related seizure occurrence [Abstract]

Purpose: Investigating the daytime‐related patterns of sei-zure presentation might provide important insights into theinvolved epileptogenic networks. However, the alterationsof brain structural integrity linked to different profiles ofseizure occurrence are still not clear. In this study weaddressed the structural magnetic resonance imaging(MRI)‐derived features of the involved cortical and subcor-tical substrates. Method: In 13 patients (mean age ± standard deviation:28±9 years; 9 male) with nocturnal seizures (NS), 12patients (26±9; 3 male) with diurnal seizures (DS) and 10healthy controls (HC) (28±4; 6 male) 3D 3T MRI was per-formed. Cortical and subcortical volumes (hippocampus,amygdala, thalamus) were extracted with the FreeSurferprocessing stream and the between‐group differencesassessed with analysis of variance (ANOVA) and Bonfer-roni post hoc tests. There was no difference between thegroups regarding age (F2,32= 0.26, p = 0.77) and gender(χ†= 5.103, df = 2, p = 0.08). Results: NS group in contrast to DS group showed largervolumes of bilateral insula, superior temporal and orbito-frontal cortices (p = 0.05, corrected). In patients with NScortical volumes of left postcentral and right middle tempo-ral cortices were smaller in comparison to HC. Patientswith DS in comparison to HC displayed reduced corticalvolumes mainly in frontal, temporal and parietal lobes ofthe right hemisphere. Hippocampus analysis showed a sig-nificant group difference (F2,32= 3.643, p = 0.03) withpost hoc test indicating larger volumes in NS group(8208.6±1006.1) vs DS group (3859.1±508.1 mm‡,p = 0.02). For amygdala, ANOVA showed a similar signif-icant group difference (F2,32= 4.341, p = 0.02) with largervolumes in NS group (1797.3±323.2 mm‡) vs DS group(1500.5±246.2 mm‡, p = 0.03). There were no differencesin thalamic volumes between the studied groups. Conclusion: Despite epileptogenesis daytime‐related sei-zures have distinct structural correlates. These alterationscan assign protective or susceptibility properties linked tovigilance or sleep states that could be useful for therapeuticdecisions

Observation of Dirac plasmons in a topological insulator

Plasmons are the quantized collective oscillations of electrons in metals and doped semiconductors. The plasmons of ordinary, massive electrons are since a long time basic ingredients of research in plasmonics and in optical metamaterials. Plasmons of massless Dirac electrons were instead recently observed in a purely two-dimensional electron system (2DEG)like graphene, and their properties are promising for new tunable plasmonic metamaterials in the terahertz and the mid-infrared frequency range. Dirac quasi-particles are known to exist also in the two-dimensional electron gas which forms at the surface of topological insulators due to a strong spin-orbit interaction. Therefore,one may look for their collective excitations by using infrared spectroscopy. Here we first report evidence of plasmonic excitations in a topological insulator (Bi2Se3), that was engineered in thin micro-ribbon arrays of different width W and period 2W to select suitable values of the plasmon wavevector k. Their lineshape was found to be extremely robust vs. temperature between 6 and 300 K, as one may expect for the excitations of topological carriers. Moreover, by changing W and measuring in the terahertz range the plasmonic frequency vP vs. k we could show, without using any fitting parameter, that the dispersion curve is in quantitative agreement with that predicted for Dirac plasmons.Comment: 11 pages, 3 figures, published in Nature Nanotechnology (2013

Planar Hall effect from the surface of topological insulators

A prominent feature of topological insulators (TIs) is the surface states comprising of spin-nondegenerate massless Dirac fermions. Recent technical advances have made it possible to address the surface transport properties of TI thin films by tuning the Fermi levels of both top and bottom surfaces. Here we report our discovery of a novel planar Hall effect (PHE) from the TI surface, which results from a hitherto-unknown resistivity anisotropy induced by an in-plane magnetic field. This effect is observed in dual-gated devices of bulk-insulating Bi2−x Sb x Te3 thin films, where the field-induced anisotropy presents a strong dependence on the gate voltage with a characteristic two-peak structure near the Dirac point. The origin of PHE is the peculiar time-reversal-breaking effect of an in-plane magnetic field, which anisotropically lifts the protection of surface Dirac fermions from backscattering. The observed PHE provides a useful tool to analyze and manipulate the topological protection of the TI surface

Cross sections for the γp→K*+Λ and γp→K*+Σ0 reactions measured at CLAS

The first high-statistics cross sections for the reactions γp→K*+Λ and γp→K*+Σ0 were measured using the CLAS detector at photon energies between threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. Differential cross sections are presented over the full range of the center-of-mass angles, and then fitted to Legendre polynomials to extract the total cross section. Results for the K*+Λ final state are compared with two different calculations in an isobar and a Regge model, respectively. Theoretical calculations significantly underestimate the K*+Λ total cross sections between 2.1 and 2.6 GeV, but are in better agreement with present data at higher photon energies