High spatial resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogenvacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor based on its atomic size and quantum-limited sensing capabilities afforded by long spin coherence times. Although the NV center has been successfully implemented as a nanoscale scanning magnetic probe at room temperature, it has remained an outstanding challenge to extend this capability to cryogenic temperatures, where many solid-state systems exhibit non-trivial magnetic order. Here we present NV magnetic imaging down to 6 K with 6 nm spatial resolution and 3 μT/√Hz field sensitivity, first benchmarking the technique with a magnetic hard disk sample, then utilizing the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with Tc = 30 K. The expansion of NVbased magnetic imaging to cryogenic temperatures represents an important advance in state-of-theart magnetometry, which will enable future studies of heretofore inaccessible nanoscale magnetism in condensed matter systems. and Lorentz transmission electron microscopy (TEM) 7 , and reciprocal space techniques including neutron scattering 8 have been successfully utilized to study magnetism in these systems. However, each of these techniques has limitations that must be considered. In MFM, a ferromagnetic tip must be placed in close proximity to a sample, which can perturb the magnetic order that is being probed.Scanning SQUIDs typically require a probe temperature of 10 K or lower, and generally offer micron-size spatial resolution, although recent studies have enhanced the resolution to submicron scales 9 . Lorentz TEM can provide images with high spatial resolution and magnetic contrast, but requires very thin samples, typically less than 100 nm thick. Neutron scattering requires the growth of large, high purity single-crystal samples, and is an ensemble-averaged measurement. There is therefore a significant opportunity to develop a real-space, non-invasive magnetic sensor capable of studying magnetic order at sub-10 nm spatial resolution and sub-T/Hz DC field sensitivities.The nitrogen vacancy (NV) defect center in diamond is an exceptionally versatile single spin system with unique quantum properties that have driven its application in diverse areas ranging from quantum information and photonics to quantum metrology [10][11][12][13][14][15][16][17][18][19] . Cryogenic scanning magnetometry stands out as potentially the most impactful application of NV centers, taking advantage of the exquisite magnetic field sensitivity and intrinsic atomic scale of the NV center for high resolution imaging 20 . The operation of an NV-based magnetic probe is dependent on a fundamentally different sensing principle than other imaging methods, namely the spin-dependent photolum...

Vapour bubbles nucleating at micro-cavities etched into the silicon bottom plate of a cylindrical Rayleigh-Bénard sample (diameter D = 8.8 cm, aspect ratio Γ ≡ D/L 1.00 where L is the sample height) were visualized from the top and from the side. A triangular array of cylindrical micro-cavities (with a diameter of 30 µm and a depth of 100 µm) covered a circular centred area (diameter of 2.5 cm) of the bottom plate. Heat was applied to the sample only over this central area while cooling was over the entire top-plate area. Bubble sizes and frequencies of departure from the bottom plate are reported for a range of bottom-plate superheats T b − T on (T b is the bottom-plate temperature, T on is the onset temperature of bubble nucleation) from 3 to 12 K for three different cavity separations. The difference T b − T t 16 K between T b and the top plate temperature T t was kept fixed while the mean temperature T m = (T b + T t )/2 was varied, leading to a small range of the Rayleigh number Ra from 1.4 × 10 10 to 2.0 × 10 10 . The time between bubble departures from a given cavity decreased exponentially with increasing superheat and was independent of cavity separation. The contribution of the bubble latent heat to the total enhancement of heat transferred due to bubble nucleation was found to increase with superheat, reaching up to 25 %. The bubbly flow was examined in greater detail for a superheat of 10 K and Ra 1.9 × 10 10 . The condensation and/or dissolution rates of departed bubbles revealed two regimes: the initial rate was influenced by steep thermal gradients across the thermal boundary layer near the plate and was two orders of magnitude larger than the final condensation and/or dissolution rate that prevailed once the rising bubbles were in the colder bulk flow of nearly uniform temperature. The dynamics of thermal plumes was studied qualitatively in the presence and absence of nucleating bubbles. It was found that bubbles enhanced the plume velocity by a factor of four or so and drove a large-scale circulation (LSC). Nonetheless, even in the presence of bubbles the plumes † Email address for correspondence: daniela.narezo@gmail.com Vapour-bubble nucleation and dynamics in Rayleigh-Bénard convection 61 and LSC had a characteristic velocity which was smaller by a factor of five or so than the bubble-rise velocity in the bulk. In the absence of bubbles there was strongly turbulent convection but no LSC, and plumes on average rose vertically.

No abstract

HistoryAn 8-year-old neutered male Dachshund was evaluated at the Boren Veterinary Medical Teaching Hospital with a history of stranguria, pollakiuria, and incontinence for 3 weeks and signs of back pain and slowly progressive paraparesis for 2 weeks. The dog had been treated for cystitis and suspected prostatitis by the referring veterinarian, with a 1-week course of antimicrobials and meloxicam. The urinary incontinence persisted after treatment, but there was mild improvement in the stranguria and pollakiuria and a subjective decrease in the size of the prostate gland. Approximately 2 years earlier, a T12-T13 hemilaminectomy had been performed for treatment of Hansen type 1 intervertebral disk herniation. The signs of back pain and progressive paraparesis were believed to be the result of an episode of intervertebral disk disease, and cage confinement was initiated. Three days prior to referral, administration of meloxicam was discontinued, and treatment with tramadol and prednisone was initiated. The owner reported that the dog had been dribbling urine, was only able to urinate and defecate small amounts at a time, had begun trying to bite when picked up, and was weak in the pelvic limbs.Physical examination revealed severe signs of pain in the lumbar vertebral area and caudal aspect of the abdomen, an asymmetrically enlarged and painful prostate gland, pelvic limb paraparesis, conscious proprioceptive deficits in the pelvic limbs, and pelvic limb hyperreflexia. Anal tone and perineal reflexes were normal; the urinary bladder was distended, and urine was difficult to express. Abdominal radiography was performed to evaluate the prostate gland (Figure 1).Determine whether additional imaging studies are required, or make your diagnosis from Figure 1-then turn the page → Figure 1-Lateral (A) and ventrodorsal (B) radiographic views of the abdomen of an 8-year-old neutered male Dachshund evaluated because of a 3-week history of stranguria, pollakiuria, and signs of pain on palpation over the lumbar vertebral area (L3-L4 region).