The pumpistor: a linearized model of a flux-pumped SQUID for use as a negative-resistance parametric amplifier

We describe a circuit model for a flux-driven SQUID. This is useful for developing insight into how these devices perform as active elements in parametric amplifiers. The key concept is that frequency mixing in a flux-pumped SQUID allows for the appearance of an effective negative resistance. In the three-wave, degenerate case treated here, a negative resistance appears only over a certain range of allowed input signal phase. This model readily lends itself to testable predictions of more complicated circuits.Comment: 4 pages, 3 figure

Characterization of a multimode coplanar waveguide parametric amplifier

We characterize a novel Josephson parametric amplifier based on a flux-tunable quarter-wavelength resonator. The fundamental resonance frequency is ~1GHz, but we use higher modes of the resonator for our measurements. An on-chip tuning line allows for magnetic flux pumping of the amplifier. We investigate and compare degenerate parametric amplification, involving a single mode, and nondegenerate parametric amplification, using a pair of modes. We show that we reach quantum-limited noise performance in both cases, and we show that the added noise can be less than 0.5 added photons in the case of low gain

A risk assessment scale for the prediction of pressure sore development: reliability and validity

Background. The ability to assess the risk of a patient developing pressure sores is a major issue in pressure sore prevention. Risk assessment scales should be valid, reliable and easy to use in clinical practice. Aim. To develop further a risk assessment scale, for predicting pressure sore development and, in addition, to present the validity and reliability of this scale. Methods. The risk assessment pressure sore (RAPS) scale, includes 12 variables, five from the re-modified Norton scale, three from the Braden scale and three from other research results. Five hundred and thirty patients without pressure sores on admission were included in the study and assessed over a maximum period of 12 weeks. Internal consistency was examined by item analysis and equivalence by interrater reliability. To estimate equivalence, 10 pairs of nurses assessed a total of 116 patients. The underlying dimensions of the scale were examined by factor analysis. The predictive validity was examined by determination of sensitivity, specificity and predictive value. Results. Two variables were excluded as a result of low item–item and item–total correlations. The average percentage of agreement and the intraclass correlation between raters were 70% and 0·83, respectively. The factor analysis gave three factors, with a total variance explained of 65·1%. Sensitivity, specificity and predictive value were high among patients at medical and infection wards. Conclusions. The RAPS scale is a reliable scale for predicting pressure sore development. The validity is especially good for patients undergoing treatment in medical wards and wards for infectious diseases. This indicates that the RAPS scale may be useful in clinical practice for these groups of patients. For patients undergoing surgical treatment, further analysis will be performed.måsjekke

Absolute rate coefficients for photorecombination of berylliumlike and boronlike silicon ions

We report measured rate coefficients for electron-ion recombination for Si10+ forming Si9+ and for Si9+ forming Si8+, respectively. The measurements were performed using the electron-ion merged-beams technique at a heavy-ion storage ring. Electron-ion collision energies ranged from 0 to 50 eV for Si9+ and from 0 to 2000 eV for Si10+, thus, extending previous measurements for Si10+ [Orban et al. 2010, Astrophys. J. 721, 1603] to much higher energies. Experimentally derived rate coefficients for the recombination of Si9+ and Si10+ ions in a plasma are presented along with simple parameterizations. These rate coefficients are useful for the modeling of the charge balance of silicon in photoionized plasmas (Si9+ and Si10+) and in collisionally ionized plasmas (Si10+ only). In the corresponding temperature ranges, the experimentally derived rate coefficients agree with the latest corresponding theoretical results within the experimental uncertainties.Comment: 17 pages, 7 figures, 3 tables, 66 references, submitted to the J. Phys. B special issue on atomic and molecular data for astrophysicist

Single-shot Readout of a Superconducting Qubit using a Josephson Parametric Oscillator

We propose and demonstrate a new read-out technique for a superconducting qubit by dispersively coupling it to a Josephson parametric oscillator. We employ a tunable quarter-wavelength superconducting resonator and modulate its resonant frequency at twice its value with an amplitude surpassing the threshold for parametric instability. We map the qubit states onto two distinct states of classical parametric oscillation: one oscillating state, with $185\pm15$ photons in the resonator, and one with zero oscillation amplitude. This high contrast obviates a following quantum-limited amplifier. We demonstrate proof-of-principle, single-shot readout performance, and present an error budget indicating that this method can surpass the fidelity threshold required for quantum computing.Comment: 11 pages, 5 figure

Absolute rate coefficients for photorecombination and electron-impact ionization of magnesium-like iron ions from measurements at a heavy-ion storage ring

Rate coefficients for photorecombination (PR) and cross sections for electron-impact ionization (EII) of Fe$^{14+}$ forming Fe$^{13+}$ and Fe$^{15+}$, respectively, have been measured by employing the electron-ion merged-beams technique at a heavy-ion storage ring. Rate coefficients for PR and EII of Fe$^{14+}$ ions in a plasma are derived from the experimental measurements. Simple parametrizations of the experimentally derived plasma rate coefficients are provided for use in the modeling of photoionized and collisionally ionized plasmas. In the temperature ranges where Fe$^{14+}$ is expected to form in such plasmas the latest theoretical rate coefficients of Altun et al. [Astron. Astrophys. 474, 1051 (2007)] for PR and of Dere [Astron. Astrophys. 466, 771 (2007)] for EII agree with the experimental results to within the experimental uncertainties. Common features in the PR and EII resonance structures are identified and discussed.Comment: 12 pages, 6 figures, 3 tables, submitted for publication to Physical Review

Raman study of carrier-overdoping effects on the gap in high-Tc superconducting cuprates

Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K) and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g} polarizations were largely shifted to the low energies close to a half of 2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-T_c superconducting cuprates.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B, Rapid communicaito

Dissociative recombination measurements of HCl+ using an ion storage ring

We have measured dissociative recombination of HCl+ with electrons using a merged beams configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present the measured absolute merged beams recombination rate coefficient for collision energies from 0 to 4.5 eV. We have also developed a new method for deriving the cross section from the measurements. Our approach does not suffer from approximations made by previously used methods. The cross section was transformed to a plasma rate coefficient for the electron temperature range from T=10 to 5000 K. We show that the previously used HCl+ DR data underestimate the plasma rate coefficient by a factor of 1.5 at T=10 K and overestimate it by a factor of 3.0 at T=300 K. We also find that the new data may partly explain existing discrepancies between observed abundances of chlorine-bearing molecules and their astrochemical models.Comment: Accepted for publication in ApJ (July 7, 2013

Electronic Raman-scattering study of low-energy excitations in single and double CuO_2-layer Tl-Ba-(Ca)-Cu-O superconductors

Low energy Raman continuum and the redistribution of the continuum to a peak (2\Delta-peak) in the superconducting state have been studied in Tl-Ba-(Ca)-Cu-O superconductors with single (Tl-2201) and double (Tl-2212) CuO_2 layer. The 2\Delta/k_BT_c ratios in A_1g and B_1g symmetries are larger for Tl-2212 than for Tl-2201. The B_1g/A_1g gap ratio is also larger in Tl-2212. The A_1g intensities of the continuum and the 2\Delta-peak are significantly weaker than the B_1g intensities in Tl-2201, but are comparable in Tl-2212. This shows that the Coulomb screening is much stronger in Tl-2201. The change from Tl-2201 to Tl-2212 of the normalized A_1g 2\Delta-peak intensity is identical within experimental error to that of normalized A_1g continuum intensity. This suggests that the excitations forming the 2\Delta-peak and the continuum couple to light by the same mechanism.Comment: 4 pages, PDF forma