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The desire to improve the corrosion resistance of Zr cladding material for high burn-up has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While commonly accepted, the reason for the improved corrosion performance observed for low-tin zirconium alloys in high-temperature aqueous environments remains unclear. High-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr–Sn–Nb alloys with tin concentration ranging from 0.01 to 0.92wt.%. The alloys studied included the commercial alloy ZIRLO® (ZIRLO® is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited.) and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy was investigated via cross-sectional scanning electron microscopy. Atom probe analysis of ZIRLO demonstrated that the tin present in the alloy passes into the oxide as it forms, with no significant difference in the Sn/Zr ratio between the two. Synchrotron X-ray diffraction measurements on the oxides formed on each alloy revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on the phase and alloy. The amount of tetragonal phase present and, more importantly, the level of tetragonal-to-monoclinic phase transformation both decrease with decreasing tin levels, suggesting that tin is a tetragonal oxide phase stabilizing element. It is proposed that in Zr–Nb–Sn alloys with low Sn, the tetragonal phase is mainly stabilized by very small grain size and therefore remains stable throughout the corrosion process. In contrast, alloys with higher tin levels can in addition grow larger, stress stabilized, tetragonal grains that become unstable as the corrosion front continues to grow further inwards and stresses in the existing oxide relax. [ABSTRACT FROM AUTHOR]

Abstract: To improve the understanding of the oxidation mechanism in zirconium alloys for fuel clad applications, detailed residual stress and phase fraction analysis was carried out for the oxides formed on Zircaloy-4 after autoclave exposure at 360°C for various times by means of synchrotron X-ray diffraction. In a post-transition sample (220days), significant stress variation through the oxide thickness was found for the monoclinic phase in individual oxide layers, with maximum in-plane compressive stresses located towards the metal–oxide interface and a discontinuity in the residual stress profile. The depth of this discontinuity matched well with the depth at which electron microscopy analysis showed an interface between two distinct oxide layers. Analysis of the tetragonal phase with exposure time demonstrated changes of the total volume of tetragonal phase before and during transition. These observations are put into the context of residual stress evolution presented previously, to provide further insight into the importance of phase transformations and residual stresses in determining the corrosion kinetics of Zr alloys. [Copyright &y& Elsevier]

Abstract: Aqueous corrosion and hydrogenation have become major limiting factors to the use of zirconium alloys as fuel cladding and assembly components in water-cooled nuclear reactors. The metal–oxide interface has been a particular focus of previous research, but there is still no clear understanding of what is present at the interface at different stages of the complex oxidation process. We report here a systematic investigation using state-of-the-art instrumentation on the interfaces in several zirconium alloys corroded for different times. We have shown that thin intermediate oxide layers with compositions close to ZrO can be observed in almost all the pre-transition samples studied, and that this layer thickens during the pre-transition stage. Just before the kinetic transition, a large variation in the suboxide width was detected, suggesting that the kinetic transition is an extremely local process. After transition the suboxide was generally absent. In the suboxide locations different structures, including an unidentified phase, were found. The oxygen-saturated (∼30at.% O) metal regions found beneath the oxide are thickest in the (late) pre-transition samples and significantly thinner in the post-transition samples. We suggest that the suboxide cannot by itself act as a protective layer and conclude that it is the development of interlinked porosity down to the metal–oxide interface that is the reason for the transition in oxidation kinetics. [Copyright &y& Elsevier]

Autoclave corrosion experiments were conducted on a number of zirconium alloys in different heat treatment conditions. The alloys tested in the present work were Zircaloy-4, ZIRLO® (ZIRLO is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorised use is strictly prohibited.) and two variants of ZIRLO with significantly lower Sn levels, referred to here as A-0·6Sn and A-0·0Sn. Typical corrosion kinetics with a change from pre- to post-initial transition was observed with ZIRLO and Zircaloy-4 displaying the shortest time to the initial transition after 120-140 days of autoclave exposure, followed by A-0·6Sn materials after 140-260 days. A-0·0Sn materials showed no sign of transition even after 360 days although one sample tested to 540 days had gone through transition. Material in the stress relieved condition generally experienced initial transition earlier than the same alloy in the recrystallised condition. Pretransition samples had a universally black oxide layer, which eventually developed grey patches when transition occurred. Practically, all non-hydrogen charged alloys showed a strong trend towards cubic oxide growth rates. Cathodic hydrogen charging was conducted to simulate end of life condition of cladding tubes, forming a hydride rich rim region at the outer surface of the cladding tubes. Hydrogen charged materials generally experienced accelerated corrosion of different degrees with the exception of recrystallised A-0·0Sn and partially recrystallised A-0·6Sn showing no sign of acceleration. It therefore seems that increasing tin levels has a negative impact on autoclave corrosion behaviour for materials with and without a hydride rich rim. In developing advanced alloys for use in cladding, this effect has been balanced against the benefits that Sn is known to provide in-reactor, including robustness in corrosion behaviour and reduced irradiation growth. It was noted that most materials with a hydride rich rim exhibit parabolic corrosion kinetics with decreased initial weight gain but increased overall weight gain. [ABSTRACT FROM AUTHOR]

The ESR response from highly metal-semiconductor (M-SC) separated single-walled carbon nanotubes (SWCNTs) for temperatures T between 0.39 and 200 K is characteristically different for the two systems. The signal originates from defect spins but interaction with free electrons leads to a larger linewidth for M tubes. The latter decreases with increasing T, whereas it increases with T for SC tubes. The spins undergo a ferromagnetic phase transition below around 10 K. Indirect exchange is suggested to be responsible for the spin-spin interaction, supported by RKKY interaction in the case of M tubes. For SC tubes, the spin-lattice relaxation via an Orbach process is suggested to determine the linewidth. [ABSTRACT FROM AUTHOR]

We have performed continuous wave and pulsed electron spin resonance measurements of implanted bismuth donors in isotopically enriched silicon-28. Donors are electrically activated via thermal annealing with minimal diffusion. Damage from bismuth ion implantation is repaired during thermal annealing as evidenced by narrow spin resonance linewidths (Bpp=12μT) and long spin coherence times (T2=0.7 ms, at temperature T=8 K). The results qualify ion implanted bismuth as a promising candidate for spin qubit integration in silicon. [ABSTRACT FROM AUTHOR]

Dynamical decoupling (DD) is an efficient tool for preserving quantum coherence in solid-state spin systems. However, the imperfections of real pulses can ruin the performance of long DD sequences. We investigate the accumulation and compensation of different pulse errors in DD using the electron spins of phosphorus donors in silicon as a test system. We study periodic DD sequences based on spin rotations about two perpendicular axes, and their concatenated and symmetrized versions. We show that pulse errors may quickly destroy some spin states, but maintain other states with high fidelity over long times. Pulse sequences based on spin rotations about x and y axes outperform those based on x and z axes due to the accumulation of pulse errors. Concatenation provides an efficient way to suppress the impact of pulse errors, and can maintain high fidelity for all spin components: pulse errors do not accumulate (to first order) as the concatenation level increases, despite the exponential increase in the number of pulses. A symmetrized DD sequence cancels the first-order pulse errors. Our theoretical model gives a clear qualitative picture of the error accumulation and produces results in quantitative agreement with the experiments. [ABSTRACT FROM AUTHOR]

Unprecedented transport efficiency is demonstrated for electrons on the surface of micron-scale superfluid helium-filled channels by co-opting silicon processing technology to construct the equivalent of a charge-coupled device. Strong fringing fields lead to undetectably rare transfer failures after over a billion cycles in two dimensions. This extremely efficient transport is measured in 120 channels simultaneously with packets of up to 20 electrons, and down to singly occupied pixels. These results point the way towards the large scale transport of either computational qubits or electron spin qubits used for communications in a hybrid qubit system. [ABSTRACT FROM AUTHOR]

We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity. [ABSTRACT FROM AUTHOR]

Traumatic vascular injuries involving the extremity are rare and penetrating trauma accounts for the majority of such injuries. The remaining arterial injuries are as a result of either blunt or iatrogenic injuries. The rapid detection, localisation and characterisation of vascular injuries in patients who have a traumatic extremity injury is essential for the effective management and treatment of such injuries. This review will discuss the expanding role of multi-detector computed tomography angiography in diagnosing vascular injuries and its implications on conventional diagnostic angiography. The roles of other non-invasive imaging modalities are reviewed. The presentation and types of vascular injuries in blunt and penetrating injuries are discussed. While surgery remains the gold standard in the management of vascular extremity injuries it has significant morbidity rates. Endovascular techniques are increasingly being used for the treatment of vascular traumatic injuries and various techniques including balloon occlusion, embolisation and stent/stent graft placement are discussed. [ABSTRACT FROM AUTHOR]

We analyze the thermodynamic characteristics and specific features of the course of reactions of oxometalate reduction on the aluminum surface and the properties of the final products (the specific electric resistance of oxides). The absence of a correlation between the ranged series of these parameters led to the necessity of using artificial intellect for modeling the processes of formation of conversion coatings. We obtained and visualized in 3D space the dependences of the corrosion resistance of D16 alloy on the oxometalate concentration, pH, the time of sealing, and test duration. Artificial neural networks based on multilayer perceptrons were used for predicting the corrosion resistance of conversion coatings. [ABSTRACT FROM AUTHOR]

We show that calcium monohydrophosphate can serve as an efficient inhibiting component of anticorrosive coatings applied on an aluminum-copper alloy. It has been established that the charge-transfer resistance of D16T alloy under the influence of CaHPO4 solution approaches the value characteristic of a medium with strontium chromate. Calcium monohydrophosphate simulates the behavior of strontium chromate inhibitor, retarding the cathodic and anodic corrosion reactions on the surface of aluminum alloys. [ABSTRACT FROM AUTHOR]

Abstract: We present an investigation of the g-factor and the spin coherence time of electrons confined in regular SiGe quantum dot arrays deposited on prepatterned Si substrates. These structures were investigated by photoluminescence and electron paramagnetic resonance both in continuous wave and pulsed mode. The dot structures consist of regular arrays of about SiGe quantum dots on a Si(1 0 0) substrate that was prepatterned by e-beam lithography or holographic lithography. These quantum dot systems show an EPR line with a g-factor of conduction electrons in Si. The spin lifetime fits to that of two-dimensional SiGe structures, but the EPR line width shows inhomogeneous broadening. A 2D anisotropy is no longer visible. [Copyright &y& Elsevier]

We investigate spin relaxation and the g-factor of conduction electrons in modulation doped Si/SiGe quantum wells by means of electron spin resonance. We find that both the transverse- and the longitudinal relaxation times are of the order of microseconds, much longer than in III–V compounds. For high mobility, at carrier densities sufficiently far away from the metal-to-insulator transition, both quantities can be explained consistently in terms of the Bychkov–Rashba field, together with the g-factor anisotropy and its dependence on the carrier density. A single value of the BR coefficient, αBR=0.55×10−12 eV cm, explains all data. This value is by more than three orders of magnitude smaller than for III–V compounds owing to the small spin–orbit coupling of Si. The properties found make Si/SiGe quantum structures interesting candidates for quantum computing. [Copyright &y& Elsevier]

Abstract: Tilted field magnetotransport study was performed in a two-valley strained Si quantum well and hysteretic diagonal resistance spikes were observed near the coincidence angles. The spike around filling factor develops into a giant feature when it moves to the high-field edge of the quantum Hall (QH) state and quenches for higher tilt angles. When the spike is most prominent, its peak resistance is temperature independent from T∼20mK up to 0.3K, which is different from the critical behavior previously reported near the Curie temperature of the QH ferromagnet in AlAs quantum wells. Our data suggest a strong interplay between spins and valleys near the coincidence. [Copyright &y& Elsevier]

We characterize a fluxonium qubit consisting of a Josephson junction inductively shunted with a NbTiN nanowire superinductance. We explain the measured energy spectrum by means of a multimode theory accounting for the distributed nature of the superinductance and the effect of the circuit nonlinearity to all orders in the Josephson potential. Using multiphoton Raman spectroscopy, we address multiple fluxonium transitions, observe multilevel Autler-Townes splitting and measure an excited state lifetime of T1=20 μs. By measuring T1 at different magnetic flux values, we find a crossover in the lifetime limiting mechanism from capacitive to inductive losses. [ABSTRACT FROM AUTHOR]

Donor electron spins in semiconductors make exceptional qubits because of their long coherence times and compatibility with industrial fabrication techniques. Despite many advances in donor-based qubit technology, it remains difficult to selectively manipulate single-donor electron spins. Here, we show that by replacing the prevailing semiconductor host material (silicon) with germanium, donor electron spin qubits can be electrically tuned by more than an ensemble linewidth, making them compatible with gate-addressable quantum computing architectures. Using X-band pulsed electron spin resonance, we measured the Stark effect for donor electron spins in germanium. We resolved both spin-orbit and hyperfine Stark shifts and found that at 0.4 T, the spin-orbit Stark shift dominates. The spin-orbit Stark shift is highly anisotropic, depending on the electric field orientation relative to the crystal axes and external magnetic field. When the Stark shift is maximized, the spin-orbit Stark parameter is four orders of magnitude larger than in silicon. At select orientations a hyperfine Stark effect was also resolved and is an order of magnitude larger than in silicon. We report the Stark parameters for 75As and 31P donor electrons and compare them to the available theory. Our data reveal that 31P donors in germanium can be tuned by at least four times the ensemble linewidth, making germanium an appealing new host material for spin qubits that offers major advantages over silicon. [ABSTRACT FROM AUTHOR]

Spectral diffusion arising from 29Si nuclear spin flip-flops, known to be a primary source of electron spin decoherence in silicon, is also predicted to limit the coherence times of neutral donor nuclear spins in silicon. Here, the impact of this mechanism on 31P nuclear spin coherence is measured as a function of 29Si concentration using X-band pulsed electron nuclear double resonance. The P31 nuclear spin echo decays show that decoherence is controlled by 29Si flip-flops resulting in both fast (exponential) and slow (nonexponential) spectral diffusion processes. The decay times span a range from 100 ms in crystals containing 50% 29Si to 3 s in crystals containing 1% 29Si. These nuclear spin echo decay times for neutral donors are orders of magnitude longer than those reported for ionized donors in natural silicon. The electron spin of the neutral donors "protects" the donor nuclear spins by suppressing 29Si flip-flops within a "frozen core," as a result of the detuning of the 29Si spins caused by their hyperfine coupling to the electron spin. [ABSTRACT FROM AUTHOR]

Over the past decade, donor spin qubits in isotopically enriched 28Si have been intensely studied due to their exceptionally long coherence times. More recently, bismuth donor electron spins have become popular because Bi has a large nuclear spin which gives rise to clock transitions (first-order insensitive to magnetic field noise). At every clock transition there are two nearly degenerate transitions between four distinct states which can be used as a pair of qubits. Here it is experimentally demonstrated that these transitions are excited by microwaves of opposite helicity such that they can be selectively driven by varying microwave polarization. This work uses a combination of a superconducting coplanar waveguide (CPW) microresonator and a dielectric resonator to flexibly generate arbitrary elliptical polarizations while retaining the high sensitivity of the CPW. [ABSTRACT FROM AUTHOR]

We report on electron spin resonance measurements of phosphorus donors localized in a 200  μm^{2} area below the inductive wire of a lumped element superconducting resonator. By combining quantum limited parametric amplification with a low impedance microwave resonator design, we are able to detect around 2×10^{4} spins with a signal-to-noise ratio of 1 in a single shot. The 150 Hz coupling strength between the resonator field and individual spins is significantly larger than the 1-10 Hz coupling rates obtained with typical coplanar waveguide resonator designs. Because of the larger coupling rate, we find that spin relaxation is dominated by radiative decay into the resonator and dependent upon the spin-resonator detuning, as predicted by Purcell.

Clostridium difficile is commonly associated with a spectrum of disease in humans referred to as C. difficile-associated disease (CDAD) and use of antimicrobials is considered a risk factor for development of disease in humans. C. difficile can also inhabit healthy food animals and transmission to humans is possible. As a result of the complexity and cost of testing, C. difficile is rarely tested for antimicrobial susceptibility. A total of 376 C. difficile strains (94 each from swine and dairy feces, and 188 from beef cattle feces) were isolated from healthy food animals on farms during studies conducted by the National Animal Health Monitoring System. Using the Etest (AB Biodisk, Solna, Sweden), samples were tested for susceptibility to nine antimicrobials implicated as risk factors for CDAD (linezolid, amoxicillin-clavulanic acid, ampicillin, clindamycin, erythromycin, levofloxacin, metronidazole, rifampicin, and vancomycin). Vancomycin was active against all isolates of C. difficile (MIC90=3.0μg/ml) while almost all isolates (n=369; 98.1%) were resistant to levofloxacin. With the exception of vancomycin, resistance varied by animal species as follows: linezolid (8.5% resistance among swine versus 2.1 and 1.1% resistance among dairy and beef, respectively), clindamycin (56.4% resistance among swine versus 80% and 90.9% resistance among dairy and beef, respectively), and rifampicin (2.1% and 0% resistance among swine and dairy cattle isolates, respectively versus 14.3% resistance among beef isolates). Regardless of species, multiple drug resistance was observed most often to combinations of clindamycin and levofloxacin (n=195; 51.9%) and ampicillin, clindamycin and levofloxacin (n=41; 10.9%). The reason for the variability of resistance between animal species is unknown and requires further research., (Published by Elsevier B.V.)

Silicon is one of the most promising semiconductor materials for spin-based information processing devices. Its advanced fabrication technology facilitates the transition from individual devices to large-scale processors, and the availability of a (28)Si form with no magnetic nuclei overcomes a primary source of spin decoherence in many other materials. Nevertheless, the coherence lifetimes of electron spins in the solid state have typically remained several orders of magnitude lower than that achieved in isolated high-vacuum systems such as trapped ions. Here we examine electron spin coherence of donors in pure (28)Si material (residual (29)Si concentration <50 ppm) with donor densities of 10(14)-10(15) cm(-3). We elucidate three mechanisms for spin decoherence, active at different temperatures, and extract a coherence lifetime T(2) up to 2 s. In this regime, we find the electron spin is sensitive to interactions with other donor electron spins separated by ~200 nm. A magnetic field gradient suppresses such interactions, producing an extrapolated electron spin T(2) of 10 s at 1.8 K. These coherence lifetimes are without peer in the solid state and comparable to high-vacuum qubits, making electron spins of donors in silicon ideal components of quantum computers, or quantum memories for systems such as superconducting qubits.

We have measured the electrically detected magnetic resonance of donor-doped silicon field-effect transistors in resonant X- (9.7 GHz) and W-band (94 GHz) microwave cavities. The two-dimensional electron gas resonance signal increases by 2 orders of magnitude from X to W band, while the donor resonance signals are enhanced by over 1 order of magnitude. Bolometric effects and spin-dependent scattering are inconsistent with the observations. We propose that polarization transfer from the donor to the two-dimensional electron gas is the main mechanism giving rise to the spin resonance signals.

Electron spin qubits in molecular systems offer high reproducibility and the ability to self-assemble into larger architectures. However, interactions between neighboring qubits are "always on," and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both effectively turn on or off interqubit coupling mediated by dipolar interactions and benefit from the long nuclear spin decoherence times (T(2n)). We transfer qubit states between the electron and (15)N nuclear spin in (15)N@C(60) with a two-way process fidelity of 88%, using a series of tuned microwave and radio frequency pulses and measure a nuclear spin coherence lifetime of over 100 ms.

We propose a hybrid architecture in which an on-chip high finesse superconducting cavity is coupled to the lateral motion and spin state of a single electron trapped on the surface of superfluid helium. We estimate the motional coherence times to exceed 15  μs, while energy will be coherently exchanged with the cavity photons in less than 10 ns for charge states and faster than 1  μs for spin states, making the system attractive for quantum information processing and strong coupling cavity quantum electrodynamics experiments. The cavity is used for nondestructive readout and as a quantum bus mediating interactions between distant electrons or an electron and a superconducting qubit.

We report Stark shift measurements for 121Sb donor electron spins in silicon using pulsed electron spin resonance. Interdigitated metal gates on a Sb-implanted 28Si epilayer are used to apply the electric fields. Two quadratic Stark effects are resolved: a decrease of the hyperfine coupling between electron and nuclear spins of the donor and a decrease in electron Zeeman g factor. The hyperfine term prevails at magnetic fields of 0.35 T, while the g factor term is expected to dominate at higher magnetic fields. We discuss the results in the context of the Kane model quantum computer.

We examine the temperature dependence of the electron spin relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero-field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S> or =1 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find an Arrhenius temperature dependence for N@C60 , indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170 K.

Systematic errors in spin rotation operations using simple rf pulses place severe limitations on the usefulness of the pulsed magnetic resonance methods in quantum computing applications. In particular, the fidelity of quantum logic operations performed on electron spin qubits falls well below the threshold for the application of quantum algorithms. Using three independent techniques, we demonstrate the use of composite pulses to improve this fidelity by several orders of magnitude. The observed high-fidelity operations are limited by pulse phase errors, but nevertheless fall within the limits required for the application of quantum error correction.

Understanding the mechanisms controlling the spin coherence of electrons in semiconductors is essential for designing structures for quantum computing applications. Using a pulsed electron paramagnetic resonance spectrometer, we measure spin echoes and deduce a spin coherence time (T2) of up to 3 mus for an ensemble of free two-dimensional electrons confined in a Si/SiGe quantum well. The decoherence can be understood in terms of momentum scattering causing fluctuating effective Rashba fields. Further confining the electrons into a nondegenerate (other than spin) ground state of a quantum dot can be expected to eliminate this decoherence mechanism.

Time-resolved transport of ballistic electrons in a two-dimensional electron gas has been measured with a resolution of less than 5 ps. This was accomplished by using picosecond electrical pulses to launch electrons from the emitter of a transverse magnetic focusing structure and optoelectronically sampling the collector voltage. Both plasma resonances and the ballistic transport signal are clearly resolved. The transit time appears to be somewhat longer than expected from simple Fermi velocity considerations.