Nonlinear resonance in a three-terminal carbon nanotube resonator

The RF-response of a three-terminal carbon nanotube resonator coupled to RF-transmission lines is studied by means of perturbation theory and direct numerical integration. We find three distinct oscillatory regimes, including one regime capable of exhibiting very large hysteresis loops in the frequency response. Considering a purely capacitive transduction, we derive a set of algebraic equations which can be used to find the output power (S-parameters) for a device connected to transmission lines with characteristic impedance $Z_0$.Comment: 16 pages, 8 figure

Motional Broadening in Ensembles With Heavy-Tail Frequency Distribution

We show that the spectrum of an ensemble of two-level systems can be broadened through `resetting' discrete fluctuations, in contrast to the well-known motional-narrowing effect. We establish that the condition for the onset of motional broadening is that the ensemble frequency distribution has heavy tails with a diverging first moment. We find that the asymptotic motional-broadened lineshape is a Lorentzian, and derive an expression for its width. We explain why motional broadening persists up to some fluctuation rate, even when there is a physical upper cutoff to the frequency distribution.Comment: 6 pages, 4 figure

Full-field swept-source optical coherence tomography and neural tissue classification for deep brain imaging

Optical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. Such a device can be particularly useful as a realtime neurosurgical guidance tool. We present, to our knowledge, the first full-field swept-source optical coherence tomography system operating near a wavelength of 1310 nm. The proof-of-concept system was integrated with an endoscopic probe tip, that is compatible with deep brain stimulation keyhole neurosurgery. Neuroimaging experiments were performed on ex vivo brain tissues and in vivo in rat brains. Using classification algorithms involving texture features and optical attenuation, images were successfully classified into three brain tissue types

Dust Formation and He II 4686 emission in the Dense Shell of the Peculiar Type Ib Supernova 2006jc

We present evidence for the formation of dust grains in an unusual Type Ib SN based on late-time spectra of SN 2006jc. The progenitor suffered an LBV-like outburst just 2 yr earlier, and we propose that the dust formation is a consequence of the SN blast wave overtaking that LBV-like shell. The key evidence for dust formation is (a) the appearance of a red/near-IR continuum source fit by 1600 K graphite grains, and (b) fading of the redshifted sides of He I emission lines, yielding progressively more asymmetric blueshifted lines as dust obscures receding material. This provides the strongest case yet for dust formation in any SN Ib/c. Both developments occurred between 51 and 75 d after peak, while other SNe observed to form dust did so after a few hundred days. Geometric considerations indicate that dust formed in the dense swept-up shell between the forward and reverse shocks, and not in the freely expanding SN ejecta. Rapid cooling leading to dust formation may have been aided by extremely high shell densities, as indicated by He I line ratios. The brief epoch of dust formation is accompanied by He II 4686 emission and enhanced X-ray emission. These clues suggest that the unusual dust formation in this object was not due to properties of the SN itself, but instead -- like most peculiarities of SN 2006jc -- was a consequence of the dense environment created by an LBV-like eruption 2 yr before the SN.Comment: ApJ, accepted. added some discussion and 2 figures, better title, conclusions same as previous version. 12 pages, 4 color fig

CoWBP capping barrier layer for sub 90 nm Cu interconnects

Abstract Electroless cobalt films have been obtained by deposition using a plating bath containing two reducing agents: dimethylamineborane (DMAB) and sodium hypophosphite. This formulation allows spontaneous activation on copper followed by auto catalytic electroless plating. CoWBP and CoBP films are proposed as diffusion barriers and encapsulation layers, for copper lines and via contacts for ULSI interconnect applications. The crystalline structure, chemical composition and oxidation states of the elements were studied, as well as the electrical resistivity, topography and morphology of the films. The film composition was characterized as a function of the solution composition; the barrier properties of the films were tested and an oxidation resistance study was conducted. The films were characterized and the results show that they can be applied as capping layers for ULSI copper metallization

Ginzburg-Landau vortex dynamics with pinning and strong applied currents

We study a mixed heat and Schr\"odinger Ginzburg-Landau evolution equation on a bounded two-dimensional domain with an electric current applied on the boundary and a pinning potential term. This is meant to model a superconductor subjected to an applied electric current and electromagnetic field and containing impurities. Such a current is expected to set the vortices in motion, while the pinning term drives them toward minima of the pinning potential and "pins" them there. We derive the limiting dynamics of a finite number of vortices in the limit of a large Ginzburg-Landau parameter, or \ep \to 0, when the intensity of the electric current and applied magnetic field on the boundary scale like \lep. We show that the limiting velocity of the vortices is the sum of a Lorentz force, due to the current, and a pinning force. We state an analogous result for a model Ginzburg-Landau equation without magnetic field but with forcing terms. Our proof provides a unified approach to various proofs of dynamics of Ginzburg-Landau vortices.Comment: 48 pages; v2: minor errors and typos correcte

Sensing remote nuclear spins

Sensing single nuclear spins is a central challenge in magnetic resonance based imaging techniques. Although different methods and especially diamond defect based sensing and imaging techniques in principle have shown sufficient sensitivity, signals from single nuclear spins are usually too weak to be distinguished from background noise. Here, we present the detection and identification of remote single C-13 nuclear spins embedded in nuclear spin baths surrounding a single electron spins of a nitrogen-vacancy centre in diamond. With dynamical decoupling control of the centre electron spin, the weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the centre with hyperfine coupling as weak as ~500 Hz is amplified and detected. The quantum nature of the coupling is confirmed and precise position and the vector components of the nuclear field are determined. Given the distance over which nuclear magnetic fields can be detected the technique marks a firm step towards imaging, detecting and controlling nuclear spin species external to the diamond sensor

The type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope

We present and analyse spectra of the Type IIn supernova 1994W obtained between 18 and 203 days after explosion. During the luminous phase (first 100 d) the line profiles are composed of three major components: (i) narrow P-Cygni lines with the absorption minima at -700 km/s; (ii) broad emission lines with BVZI ~4000 km/s; and (iii) broad, smooth wings, most apparent in H-alpha. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the supernova is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. We model the supernova deceleration and Thomson scattering wings to recover the density, radial extent and Thomson optical depth of the CS envelope during the first month. We reproduce the light curve with a hydrodynamical model and find it to be powered by a combination of internal energy leakage after the explosion of an extended pre-supernova (~10^15 cm) and luminosity from circumstellar interaction. We recover the pre-explosion kinematics of the CS envelope: it is close to homologous expansion with outer velocity ~1100 km/s and a kinematic age of ~1.5 yr. The CS envelope's high mass and kinetic energy, combined with its small age, strongly suggest that the CS envelope was explosively ejected about 1.5 yr before the supernova explosion.Comment: 22 pages, 21 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

SN 2011hw: Helium-Rich Circumstellar Gas and the Luminous Blue Variable to Wolf-Rayet Transition in Supernova Progenitors

We present optical photometry and spectroscopy of the peculiar Type IIn/Ibn supernova SN2011hw. Its light curve exhibits a slower decline rate than normal SNeIbc, with a peak absolute magnitude of -19.5 (unfiltered) and a secondary peak of -18.3 mag (R). Spectra of SN2011hw are unusual compared to normal SN types, most closely resembling the spectra of SNeIbn. We center our analysis on comparing SN 2011hw to the well-studied TypeIbn SN2006jc. While the two SNe have many important similarities, the differences are quite telling: compared to SN2006jc, SN2011hw has weaker HeI and CaII lines and relatively stronger H lines, its light curve has a higher luminosity and slower decline rate, and emission lines associated with the progenitor's CSM are narrower. One can reproduce the unusual continuum shape of SN2011hw with equal contributions of a 6000K blackbody and a spectrum of SN2006jc. We attribute this emission component and many other differences between the two SNe to extra opacity from a small amount of additional H in SN2011hw, analogous to the small H mass that makes SNeIIb differ from SNeIb. Slower speeds in the CSM and elevated H content suggest a connection between the progenitor of SN2011hw and the class of Ofpe/WN9 stars, which have been associated with LBVs in their hot quiescent phases between outbursts, and are H-poor - but not H-free like classical Wolf-Rayet (WR) stars. We conclude that the similarities and differences between SN2011hw and SN2006jc can be largely understood if their progenitors exploded at different points in the transitional evolution from an LBV to a WR star.Comment: 11 pages, 7 figures, submitted to MNRA