Predicting cadmium fractions in agricultural soils using proximal sensing techniques

Cadmium (Cd) accumulation in agricultural systems has caused global environmental and health concerns. Application of phosphate fertiliser to sustain plant production unintentionally accumulated Cd in agricultural soils over time. Rapid and cost-effective Cd monitoring in these soils will help to inform Cd management practices. Compared to total Cd analysis, examining chemical fractions by sequential extraction methods can provide information on the origin, availability, and mobility of soil Cd, and to assess the potential plant Cd uptake. A total of 87 air-dried topsoil (0-15 cm) samples from pastoral farms with a history of long-term application of phosphate fertiliser were analysed using wet chemistry methods for total Cd and Cd forms in exchangeable, acid soluble, metal oxides bound, organic matter bound, and residual fractions. The data acquired using three proximal sensing techniques, visible-near-infrared (vis-NIR), mid-infrared (MIR), and portable X-ray fluorescence (pXRF) spectroscopy were used as input for partial least squares regression to develop models predicting total Cd and Cd fractions. The average total Cd concentration was 0.58 mg Cd/kg soil. For total Cd, cross-validation (cv) results of models using individual vis-NIR, MIR, and pXRF data performed with normalised root mean squared error (nRMSEcv) of 26%, 30%, and 31% and concordance correlation coefficient (CCCcv) of 0.85, 0.77, and 0.75, respectively. For exchangeable Cd, model using MIR data performed with nRMSEcv of 40% and CCCcv of 0.57. For acid soluble and organic matter bound Cd, models using vis-NIR data performed with nRMSEcv of 11% and 33% and CCCcv of 0.97 and 0.84, respectively. Reflectance spectroscopy techniques could potentially be applied as complementary tools to estimate total Cd and plant available and potentially available Cd fractions for effective implementation of Cd monitoring programmes.

Roadmap on nanoscale magnetic resonance imaging

The field of nanoscale magnetic resonance imaging (NanoMRI) was started 30 years ago. It was motivated by the desire to image single molecules and molecular assemblies, such as proteins and virus particles, with near-atomic spatial resolution and on a length scale of 100 nm. Over the years, the NanoMRI field has also expanded to include the goal of useful high-resolution nuclear magnetic resonance (NMR) spectroscopy of molecules under ambient conditions, including samples up to the micron-scale. The realization of these goals requires the development of spin detection techniques that are many orders of magnitude more sensitive than conventional NMR and MRI, capable of detecting and controlling nanoscale ensembles of spins. Over the years, a number of different technical approaches to NanoMRI have emerged, each possessing a distinct set of capabilities for basic and applied areas of science. The goal of this roadmap article is to report the current state of the art in NanoMRI technologies, outline the areas where they are poised to have impact, identify the challenges that lie ahead, and propose methods to meet these challenges. This roadmap also shows how developments in NanoMRI techniques can lead to breakthroughs in emerging quantum science and technology applications. .

Mapping the phase-separated state in a 2D magnet

Intrinsic 2D magnets have recently been established as a playground for studies on fundamentals of magnetism, quantum phases, and spintronic applications. The inherent instability at low dimensionality often results in coexistence and/or competition of different magnetic orders. Such instability of magnetic ordering may manifest itself as phase-separated states. In 4f 2D materials, magnetic phase separation is expressed in various experiments; however, the experimental evidence is circumstantial. Here, we employ a high-sensitivity MFM technique to probe the spatial distribution of magnetic states in the paradigmatic 4f 2D ferromagnet EuGe2. Below the ferromagnetic transition temperature, we discover the phase-separated state and follow its evolution with temperature and magnetic field. The characteristic length-scale of magnetic domains amounts to hundreds of nanometers. These observations strongly shape our understanding of the magnetic states in 2D materials at the monolayer limit and contribute to engineering of ultra-compact spintronics.

Scanning Nitrogen-Vacancy Magnetometry of Focused-Electron-Beam-Deposited Cobalt Nanomagnets

Focused-electron-beam-induced deposition is a promising technique for patterning nanomagnets in a single step. We fabricate cobalt nanomagnets in such a process and characterize their content, saturation magnetization, and stray magnetic field profiles by using a combination of transmission electron microscopy and scanning nitrogen-vacancy (NV) magnetometry. We find agreement between the measured stray field profiles and saturation magnetization with micromagnetic simulations. We further characterize magnetic domains and grainy stray magnetic fields in the nanomagnets and their halo side-deposits. This work may aid in the evaluation of Co nanomagnets produced through focused electron-beam-induced deposition for applications in spin qubits, magnetic field sensing, and magnetic logic.

Energy dissipation on magic angle twisted bilayer graphene

Traditional Joule dissipation omnipresent in today's electronic devices is well understood while the energy loss of the strongly interacting electron systems remains largely unexplored. Twisted bilayer graphene (tBLG) is a host to interaction-driven correlated insulating phases, when the relative rotation is close to the magic angle (1.08∘). We report on low-temperature (5K) nanomechanical energy dissipation of tBLG measured by pendulum atomic force microscopy (p-AFM). The ultrasensitive cantilever tip acting as an oscillating gate over the quantum device shows dissipation peaks attributed to different fractional fillings of the flat energy bands. Local detection allows to determine the twist angle and spatially resolved dissipation images showed the existence of hundred-nanometer domains of different doping. Application of magnetic fields provoked strong oscillations of the dissipation signal at 3/4 band filling, identified in analogy to Aharonov-Bohm oscillations, a wavefunction interference present between domains of different doping and a signature of orbital ferromagnetism.

Mechanical Mode Imaging of a High-Q Hybrid hBN/Si3N4 Resonator

We image and characterize the mechanical modes of a 2D drum resonator made of hBN suspended over a high-stress Si₃N₄ membrane. Our measurements demonstrate hybridization between various modes of the hBN resonator and those of the Si₃N₄ membrane. The measured resonance frequencies and spatial profiles of the modes are consistent with finite-element simulations based on idealized geometry. Spectra of the thermal motion reveal that, depending on the degree of hybridization with modes of the heavier and higher-quality-factor Si₃N₄ membrane, the quality factors and the motional mass of the hBN drum modes can be shifted by orders of magnitude. This effect could be exploited to engineer hybrid drum/membrane modes that combine the low motional mass of 2D materials with the high quality factor of Si₃N₄ membranes for optomechanical or sensing applications.

A tunable fiber Fabry-Perot cavity for hybrid optomechanics stabilized at 4 K

We describe an apparatus for the implementation of hybrid optomechanical systems at 4 K. The platform is based on a high-finesse, micrometer-scale fiber Fabry-Perot cavity, which can be widely tuned using piezoelectric positioners. A mechanical resonator can be positioned within the cavity in the object-in-the-middle configuration by a second set of positioners. A high level of stability is achieved without sacrificing either performance or tunability, through the combination of a stiff mechanical design, passive vibration isolation, and an active Pound-Drever-Hall feedback lock incorporating a reconfigurable digital filter. The stability of the cavity length is demonstrated to be better than a few picometers over many hours both at room temperature and at 4 K.

La place d’une EOH à l’interface entre les différents acteurs dans le contact tracing COVID-19

Introduction

Le contact tracing (CT) permet d’identifier les contacts d’un cas contagieux. Dans le contexte d’épidémie à la Covid-19, c’est un outil majeur pour casser la chaîne de transmission. En ville, supervisé par la CPAM (Caisse Primaire d’Assurance Maladie) il a gagné en efficience. Dans un centre hospitalier régional, le CT des patients diagnostiqués Covid à l’hôpital a d’abord été une mission médicale. Sa réalisation était alors partielle et non systématique et dans un but de santé publique pour minimiser le risque de cas secondaires (hospitaliers ou non), l’EOH s’est portée volontaire pour le coordonner.

Matériels et méthodes

Ce projet d’organisation contact tracing a été présenté en cellule de crise COVID et au CLIN et les actions suivantes ont été pilotées par l’EOH :

– Réflexion sur une organisation du CT avec les professionnels concernés : EOH, Directeur médical de crise, Département information médicale, Direction des soins, Qualité. Parallèlement, contact avec la CPAM, interlocuteur référent pour l’envoi des données par serveur sécurisé ;

– Elaboration d’un dossier de demande de temps infirmier et secrétariat affecté à l’EOH, dédié au CT quotidiennement ;

– Création d’un formulaire informatique pour recueillir les informations du CT: période de contagiosité du patient, identification des cas contacts, co-exposés en intra-hospitalier (IH) et extra-hospitalier (EH) …

Création d’un protocole CT précisant ses étapes: réception quotidienne de la liste des patients covid (source laboratoire), tri des patients relevant du CT, identification des contacts IH via le logiciel établissement et EH au cours d’un entretien au lit du patient. Saisie des données dans le formulaire, transmission à la CPAM. Prise en charge des contacts EH et IH rentrés à domicile par la CPAM et des contact IH encore hospitalisés en lien avec l’unité de soin. Traçabilité du CT dans le dossier du patient.

Résultats

Cette organisation du CT est opérationnelle depuis le 8/02/2021. La création d’une équipe CT rattachée à l’EOH est de 1.2 équivalent temps plein infirmier et 0.5 secrétariat. Au 25/03/2021, le CT, réalisé pour 123 patients hospitalisés découverts positifs à la Covid-19, a permis d’identifier 167 contacts et 44 co-exposés, déclarés à la CPAM. Le nombre de cas contacts identifiés peut paraître faible au regard des moyens alloués. Soulignons que notre taux d’incidence local était assez bas à cette période avec peu de variants identifiés et des patients hospitalisés âgés avec une vie sociale restreinte. L’augmentation des nouveaux variantes plus contagieux avec des hospitalisations de patients plus jeunes avec une vie sociale active, risque de faire évoluer cette activité.

Conclusion

La création d’une équipe CT spécifique, rattachée à l’EOH, permet un recensement plus exhaustif des cas contacts EH, IH et des co-exposés et un traitement des données plus rapide et efficace. Ce circuit de CT clarifié permet une gestion des cas quasi en temps réel et d’atteindre l’objectif: plus vite identifié, plus vite isolé et dépisté.

Bracing adults with chronic low back pain secondary to severe scoliosis: six months results of a prospective pilot study

PURPOSE

Adult scoliosis is sometimes associated with back pain and severe curves can progress over time. Despite scoliosis has been estimated to affect up to 68% of the population over 60, there is scant literature about conservative treatment for adult scoliosis. Recently, we tested a new brace designed to alleviate pain for adult patients with chronic pain secondary to scoliosis. The study aims to test the efficacy of a prefabricated brace in reducing pain in adult scoliosis patients.

METHODS

Twenty adults (age 67.8 ± 10.5, curve 61.9 ± 12.6° Cobb) with chronic low back pain (cLBP) secondary to Idiopathic Scoliosis (IS) were included. Patients were evaluated at baseline immediately before starting with the brace and after 6 months. Outcome measures were GRS, Oswestry Disability Index (ODI), Roland Morris Questionnaire (RM), COMI. The paired t test, ANOVA and Wilcoxon tests were used for statistical analysis RESULTS: At six months, worst pain, leg pain and back pain were significantly improved: from 7.15 to 5.60, from 5.65 to 4.35 and from 6.55 to 5.25 (p < 0.05). Sixty-five percent of patients achieved the minimal clinically important difference of 2 points for worst pain and leg pain, 55% for back pain. RM and COMI improved (p < 0.05), no differences for ODI.

CONCLUSION

The prefabricated brace showed a significant improvement at 6 months of worst, leg and back pain in most patients in a group of adult women with IS and cLBP. The quality of life didn't change in a clinically significant way even if the patients reported satisfaction with the treatment. Trial registration number and date of registration: ClinicalTrials.gov Identifier: NCT02643290, December 31, 2015.

Stray-Field Imaging of a Chiral Artificial Spin Ice during Magnetization Reversal

Artificial spin ices are a class of metamaterials consisting of magnetostatically coupled nanomagnets. Their interactions give rise to emergent behavior, which has the potential to be harnessed for the creation of functional materials. Consequently, the ability to map the stray field of such systems can be decisive for gaining an understanding of their properties. Here, we use a scanning nanometer-scale superconducting quantum interference device (SQUID) to image the magnetic stray field distribution of an artificial spin ice system exhibiting structural chirality as a function of applied magnetic fields at 4.2 K. The images reveal that the magnetostatic interaction gives rise to a measurable bending of the magnetization at the edges of the nanomagnets. Micromagnetic simulations predict that, owing to the structural chirality of the system, this edge bending is asymmetric in the presence of an external field and gives rise to a preferred direction for the reversal of the magnetization. This effect is not captured by models assuming a uniform magnetization. Our technique thus provides a promising means for understanding the collective response of artificial spin ices and their interactions.

Force sensing with nanowire cantilevers

Nanometer-scale structures with high aspect ratios such as nanowires and nanotubes combine low mechanical dissipation with high resonance frequencies, making them ideal force transducers and scanning probes in applications requiring the highest sensitivity. Such structures promise record force sensitivities combined with ease of use in scanning probe microscopes. A wide variety of possible material compositions and functionalizations is available, allowing for the sensing of various kinds of forces. In addition, nanowires possess quasi-degenerate mechanical mode doublets, which allow for sensitive vectorial force and mass detection. These developments have driven researchers to use nanowire cantilevers in various force sensing applications, which include imaging of sample surface topography, detection of optomechanical, electrical, and magnetic forces, and magnetic resonance force microscopy. In this review, we discuss the motivation behind using nanowires as force transducers, explain the methods of force sensing with nanowire cantilevers, and give an overview of the experimental progress so far and future prospects of the field.

Optimized single-shot laser ablation of concave mirror templates on optical fibers

We realize mirror templates on the tips of optical fibers using a single-shot CO₂ laser ablation procedure and perform a systematic study of the influence of the pulse power, pulse duration, and laser spot size on their geometry. This investigation provides new insights into CO₂ laser ablation of optical fibers and should help improve current models. We notably find that the radius of curvature, depth, and diameter of the templates exhibit extrema as a function of the power and duration of the ablation pulse, and observe that compound convex-concave shapes can be obtained. We additionally identify regimes of ablation parameters that lead to mirror templates with favorable geometries for use in cavity quantum electrodynamics and optomechanics.

Magnetic Force Sensing Using a Self-Assembled Nanowire

We present a scanning magnetic force sensor based on an individual magnet-tipped GaAs nanowire (NW) grown by molecular beam epitaxy. Its magnetic tip consists of a final segment of single-crystal MnAs formed by sequential crystallization of the liquid Ga catalyst droplet. We characterize the mechanical and magnetic properties of such NWs by measuring their flexural mechanical response in an applied magnetic field. Comparison with numerical simulations allows the identification of their equilibrium magnetization configurations, which in some cases include magnetic vortices. To determine a NW's performance as a magnetic scanning probe, we measure its response to the field profile of a lithographically patterned current-carrying wire. The NWs' tiny tips and their high force sensitivity make them promising for imaging weak magnetic field patterns on the nanometer-scale, as required for mapping mesoscopic transport and spin textures or in nanometer-scale magnetic resonance.

Imaging Stray Magnetic Field of Individual Ferromagnetic Nanotubes

We use a scanning nanometer-scale superconducting quantum interference device to map the stray magnetic field produced by individual ferromagnetic nanotubes (FNTs) as a function of applied magnetic field. The images are taken as each FNT is led through magnetic reversal and are compared with micromagnetic simulations, which correspond to specific magnetization configurations. In magnetic fields applied perpendicular to the FNT long axis, their magnetization appears to reverse through vortex states, that is, configurations with vortex end domains or in the case of a sufficiently short FNT with a single global vortex. Geometrical imperfections in the samples and the resulting distortion of idealized magnetization configurations influence the measured stray-field patterns.

Metabolic Effects of Single-Dose Pamidronate Administration in Prostate Cancer Patients with Bone Metastases

Background

Increased osteolysis usually accompanies sclerotic bone metastases from prostate cancer. This provides a rationale for the use of bisphosphonates to treat bone pain and prevent skeletal complications.

Methods

The fasting urinary levels of calcium, hydroxyproline (OHPRO), pyridinolines (PYD), deoxypyridinolines (DPYD), collagen cross-linked N-telopeptide (NTX) and the serum values of calcium, total alkaline phosphatase and relevant bone isoenzyme, bone gla protein (BGP), carboxy-telopeptide of type I collagen (ICTP) and parathyroid hormone (PTH) were determined at baseline and on the 15th, 30th, 60th and 90th days after single-dose (90 mg) pamidronate administration in 35 consecutive prostate cancer patients with bone metastases. These biochemical indices and serum interleukin 6 (IL-6) were also measured after four days in the last consecutive 17 cases.

Results

PYD, DPYD and NTX showed a significant decrease lasting four weeks (p<0.01, <0.01 and <0.001, respectively). OHPRO and ICTP did not change significantly. The NTX decline was greater than that of PYD and DPYD (maximum percent decrease: −71.3, −23.1 and −28.2, respectively). Bone formation markers and serum calcium did not change significantly. Serum PTH showed a rapid initial increase followed by a slow decrease (p<0.001). DPYD and NTX patterns did not correlate with changes in bone pain. As observed in the last 17 cases, the maximum osteolysis inhibition after pamidronate occurred on the fourth day after drug infusion. Serum IL-6 levels showed a short-lived decrease preceded by a transient rise on the fourth day.

Conclusions

Pamidronate is able to induce a decrease in bone resorption without significantly influencing bone formation. The maximum decrease in bone resorption occurs very early. NTX is the most sensitive bone resorption marker in bisphosphonate therapy monitoring. Changes in IL-6 but not bone resorption markers may be useful in the prediction of symptomatic response.

Vectorial scanning force microscopy using a nanowire sensor

Self-assembled nanowire (NW) crystals can be grown into nearly defect-free nanomechanical resonators with exceptional properties, including small motional mass, high resonant frequency and low dissipation. Furthermore, by virtue of slight asymmetries in geometry, a NW's flexural modes are split into doublets oscillating along orthogonal axes. These characteristics make bottom-up grown NWs extremely sensitive vectorial force sensors. Here, taking advantage of its adaptability as a scanning probe, we use a single NW to image a sample surface. By monitoring the frequency shift and direction of oscillation of both modes as we scan above the surface, we construct a map of all spatial tip-sample force derivatives in the plane. Finally, we use the NW to image electric force fields distinguishing between forces arising from the NW charge and polarizability. This universally applicable technique enables a form of atomic force microscopy particularly suited to mapping the size and direction of weak tip-sample forces.

Role of the electron spin in determining the coherence of the nuclear spins in a quantum dot

A huge effort is underway to develop semiconductor nanostructures as low-noise qubits. A key source of dephasing for an electron spin qubit in GaAs and in naturally occurring Si is the nuclear spin bath. The electron spin is coupled to each nuclear spin by the hyperfine interaction. The same interaction also couples two remote nuclear spins via a common coupling to the delocalized electron. It has been suggested that this interaction limits both electron and nuclear spin coherence, but experimental proof is lacking. We show that the nuclear spin decoherence time decreases by two orders of magnitude on occupying an empty quantum dot with a single electron, recovering to its original value for two electrons. In the case of one electron, agreement with a model calculation verifies the hypothesis of an electron-mediated nuclear spin-nuclear spin coupling. The results establish a framework to understand the main features of this complex interaction in semiconductor nanostructures.

Time-Resolved Nonlinear Coupling between Orthogonal Flexural Modes of a Pristine GaAs Nanowire

We demonstrate nonlinear coupling between two orthogonal flexural modes of single as-grown GaAs nanowires. The resonant frequency of one mode can be shifted over many line widths by mechanically driving the other mode. We present time-domain measurements of the mode coupling and characterize it further by pump-probe experiments. Measurements show that a geometric nonlinearity causes the frequency of one mode to depend directly on the square amplitude of the other mode. Nearly degenerate orthogonal modes in nanowires are particularly interesting given their potential use in vectorial force sensing.

Permanent reduction of dissipation in nanomechanical Si resonators by chemical surface protection

We report on mechanical dissipation measurements carried out on thin (∼100 nm), single-crystal silicon cantilevers with varying chemical surface termination. We find that the 1-2 nm-thick native oxide layer of silicon contributes about 85% to the friction of the mechanical resonance. We show that the mechanical friction is proportional to the thickness of the oxide layer and that it crucially depends on oxide formation conditions. We further demonstrate that chemical surface protection by nitridation, liquid-phase hydrosilylation, or gas-phase hydrosilylation can inhibit rapid oxide formation in air and results in a permanent improvement of the mechanical quality factor between three- and five-fold. This improvement extends to cryogenic temperatures. Presented recipes can be directly integrated with standard cleanroom processes and may be especially beneficial for ultrasensitive nanomechanical force- and mass sensors, including silicon cantilevers, membranes, or nanowires.

Stabilized Skyrmion Phase Detected in MnSi Nanowires by Dynamic Cantilever Magnetometry

Using dynamic cantilever magnetometry we measure an enhanced skyrmion lattice phase extending from around 29 K down to at least 0.4 K in single MnSi nanowires (NWs). Although recent experiments on two-dimensional thin films show that reduced dimensionality stabilizes the skyrmion phase, our results are surprising given that the NW dimensions are much larger than the skyrmion lattice constant. Furthermore, the stability of the phase depends on the orientation of the NWs with respect to the applied magnetic field, suggesting that an effective magnetic anisotropy, likely due to the large surface-to-volume ratio of these nanostructures, is responsible for the stabilization. The compatibility of our technique with nanometer-scale samples paves the way for future studies on the effect of confinement and surfaces on magnetic skyrmions.

Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses

The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.

Quantum dot opto-mechanics in a fully self-assembled nanowire

We show that optically active quantum dots (QDs) embedded in MBE-grown GaAs/AlGaAs core-shell nanowires (NWs) are coupled to the NW mechanical motion. Oscillations of the NW modulate the QD emission energy in a broad range exceeding 14 meV. Furthermore, this opto-mechanical interaction enables the dynamical tuning of two neighboring QDs into resonance, possibly allowing for emitter-emitter coupling. Both the QDs and the coupling mechanism, i.e. material strain, are intrinsic to the NW structure and do not depend on any functionalization or external field. Such systems open up the prospect of using QDs to probe and control the mechanical state of a NW, or conversely of making a quantum nondemolition readout of a QD state through a position measurement.

Reversal mechanism of an individual Ni nanotube simultaneously studied by torque and SQUID magnetometry

Using an optimally coupled nanometer-scale SQUID, we measure the magnetic flux originating from an individual ferromagnetic Ni nanotube attached to a Si cantilever. At the same time, we detect the nanotube's volume magnetization using torque magnetometry. We observe both the predicted reversible and irreversible reversal processes. A detailed comparison with micromagnetic simulations suggests that vortexlike states are formed in different segments of the individual nanotube. Such stray-field free states are interesting for memory applications and noninvasive sensing.

Cantilever magnetometry of individual Ni nanotubes

Recent experimental and theoretical work has focused on ferromagnetic nanotubes due to their potential applications as magnetic sensors or as elements in high-density magnetic memory. The possible presence of magnetic vortex states-states which produce no stray fields-makes these structures particularly promising as storage devices. Here we investigate the behavior of the magnetization states in individual Ni nanotubes by sensitive cantilever magnetometry. Magnetometry measurements are carried out in the three major orientations, revealing the presence of different stable magnetic states. The observed behavior is well-described by a model based on the presence of uniform states at high applied magnetic fields and a circumferential onion state at low applied fields.

Probing single-charge fluctuations at a GaAs/AlAs interface using laser spectroscopy on a nearby InGaAs quantum dot

We probe local charge fluctuations in a semiconductor via laser spectroscopy on a nearby self-assembled quantum dot. We demonstrate that the quantum dot is sensitive to changes in the local environment at the single-charge level. By controlling the charge state of localized defects, we are able to infer the distance of the defects from the quantum dot with ±5  nm resolution. The results identify and quantify the main source of charge noise in the commonly used optical field-effect devices.

Force-detected nuclear magnetic resonance: recent advances and future challenges

We review recent efforts to detect small numbers of nuclear spins using magnetic resonance force microscopy. Magnetic resonance force microscopy (MRFM) is a scanning probe technique that relies on the mechanical measurement of the weak magnetic force between a microscopic magnet and the magnetic moments in a sample. Spurred by the recent progress in fabricating ultrasensitive force detectors, MRFM has rapidly improved its capability over the last decade. Today it boasts a spin sensitivity that surpasses conventional, inductive nuclear magnetic resonance detectors by about eight orders of magnitude. In this review we touch on the origins of this technique and focus on its recent application to nanoscale nuclear spin ensembles, in particular on the imaging of nanoscale objects with a three-dimensional (3D) spatial resolution better than 10 nm. We consider the experimental advances driving this work and highlight the underlying physical principles and limitations of the method. Finally, we discuss the challenges that must be met in order to advance the technique towards single nuclear spin sensitivity-and perhaps-to 3D microscopy of molecules with atomic resolution.

Isotope-selective detection and imaging of organic nanolayers

Magnetic resonance force microscopy (MRFM) makes use of the spectroscopic nature of magnetic resonance to add unambiguous elemental selectivity to scanning probe microscopy. We show isotopic selectivity of MRFM for three nuclei, (1)H, (31)P, and (13)C, in organic materials. We also detect a roughly 1 nm thick layer of naturally occurring adsorbates on a gold surface by measuring the magnetic resonance signal of the hydrogen contained in the layer. Finally, we detect the signal from hydrogen present on a carbon nanotube and use it to perform a three-dimensional magnetic resonance image of the 10 nm diameter object.

Nuclear double resonance between statistical spin polarizations

We demonstrate nuclear double resonance for nanometer-scale volumes of spins where random fluctuations rather than Boltzmann polarization dominate. When the Hartmann-Hahn condition is met in a cross-polarization experiment, flip-flops occur between two species of spins and their fluctuations become coupled. We use magnetic resonance force microscopy to measure this effect between 1H and 13C spins in 13C-enriched stearic acid. The development of a cross-polarization technique for statistical ensembles adds an important tool for generating chemical contrast in nanometer-scale magnetic resonance.

Nuclear spin relaxation induced by a mechanical resonator

We report on measurements of the spin lifetime of nuclear spins strongly coupled to a micromechanical cantilever as used in magnetic resonance force microscopy. We find that the rotating-frame correlation time of the statistical nuclear polarization is set by the magnetomechanical noise originating from the thermal motion of the cantilever. Evidence is based on the effect of three parameters: (1) the magnetic field gradient (the coupling strength), (2) the Rabi frequency of the spins (the transition energy), and (3) the temperature of the low-frequency mechanical modes. Experimental results are compared to relaxation rates calculated from the spectral density of the magnetomechanical noise.

Role of spin noise in the detection of nanoscale ensembles of nuclear spins

When probing nuclear spins in materials on the nanometer scale, random fluctuations of the spin polarization will exceed the mean Boltzmann polarization for sample volumes below about (100 nm){3}. In this Letter, we use magnetic resonance force microscopy to observe nuclear spin fluctuations in real time. We show how reproducible measurements of the polarization variance can be obtained by controlling the spin correlation time and rapidly sampling a large number of independent spin configurations. This allows significant improvement in the signal-to-noise ratio for nanometer-scale magnetic resonance imaging.

Feedback cooling of a cantilever's fundamental mode below 5 mK

We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K down to 2.9+/-0.3 mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or "squash" the optical interferometer intensity noise below the shot noise level.

Nuclear magnetic resonance imaging with 90-nm resolution

Magnetic resonance imaging (MRI) is a powerful imaging technique that typically operates on the scale of millimetres to micrometres. Conventional MRI is based on the manipulation of nuclear spins with radio-frequency fields, and the subsequent detection of spins with induction-based techniques. An alternative approach, magnetic resonance force microscopy (MRFM), uses force detection to overcome the sensitivity limitations of conventional MRI. Here, we show that the two-dimensional imaging of nuclear spins can be extended to a spatial resolution better than 100 nm using MRFM. The imaging of 19F nuclei in a patterned CaF(2) test object was enabled by a detection sensitivity of roughly 1,200 nuclear spins at a temperature of 600 mK. To achieve this sensitivity, we developed high-moment magnetic tips that produced field gradients up to 1.4 x 10(6) T m(-1), and implemented a measurement protocol based on force-gradient detection of naturally occurring spin fluctuations. The resulting detection volume was less than 650 zeptolitres. This is 60,000 times smaller than the previous smallest volume for nuclear magnetic resonance microscopy, and demonstrates the feasibility of pushing MRI into the nanoscale regime.

Reassessing the Current TNM Lymph Node Staging for Renal Cell Carcinoma

OBJECTIVE

The most commonly used staging system for renal cell carcinoma (RCC) is the tumor-node-metastasis (TNM) system. In the most recent TNM edition, lymph node (LN) involvement is defined as pN0, pN1, or pN2, depending on the number of metastatic LNs (none, 1, or >1). This study evaluated the prognostic value of this classification and tried to improve its clinical impact by considering an additional parameter, that is, LN density (ratio between number of positive LNs and total number of LNs retrieved).

METHODS

All pathologic reports of radical nephrectomies performed for RCC in two urologic centers between November 1983 and December 1999 were reviewed. For each patient, complete clinical and pathologic data, number of LNs removed, location and number of positive LNs, and LN density were recorded. The Kaplan-Meyer method and the log-rank test were used to calculate cause-specific survival rates and to compare survival curves, respectively.

RESULTS

A total of 735 patients underwent radical nephrectomy. Lymphadenectomy was performed in 618 cases, and the rate of positive LNs was 14.2%. The 5-yr cause-specific survival rate of pN+ patients was 18%, with no statistically significant difference between pN1 and pN2. The average number of LNs removed was 13 (range, 1-35). The median number of LNs involved was 3 (range, 1-18). LN density ranged between 3.7% and 100% (median, 22.9%). The number of LNs removed had no impact on survival in pN+ patients. The only significant unfavorable prognostic factors were >4 LNs involved (p = 0.02) and LN density >60% (p = 0.01).

CONCLUSION

The results show that in RCC the current TNM stratification of positive LNs is not significantly correlated with prognosis. From our data it appears that classification as < or =4 or >4 LNs involved, supported by LN density, better reflects the impact of the disease on survival.

Antiferromagnetic s-d exchange coupling in GaMnAs

Measurements of coherent electron spin dynamics in Ga1-xMnxAs/Al0.4Ga0.6As quantum wells with 0.0006%<x<0.03% show an antiferromagnetic (negative) exchange between s-like conduction band electrons and electrons localized in the d shell of the Mn2+ impurities. The magnitude of the s-d exchange parameter, N0alpha, varies as a function of well width indicative of a large and negative contribution due to kinetic exchange. In the limit of no quantum confinement, N0alpha extrapolates to -0.09+/-0.03 eV indicating that antiferromagnetic s-d exchange is a bulk property of GaMnAs. Measurements of the polarization-resolved photoluminescence show strong discrepancy from a simple model of the exchange enhanced Zeeman splitting, indicative of additional complexity in the exchange split valence band.

Prognostic value of the involvement of the urinary collecting system in renal cell carcinoma

OBJECTIVES

The prognostic role of the invasion of the urinary collecting system (UCS) by renal cell carcinoma (RCC) has not attracted a notable amount of attention. The aim of this study was to investigate incidence and prognostic value of UCS involvement in RCC.

MATERIAL AND METHODS

All pathological reports of radical nephrectomies performed in two centres of urology from November 1983 to December 1999 were reviewed in order to evaluate the invasion of the UCS (calices, renal pelvis, ureter). Patients were divided into two groups according to presence (Group 1) or absence (Group 2) of UCS invasion. The stage was determined according to the TNM 6th edition. Overall and cause-specific survival rates were evaluated. Univariate and multivariate analyses were performed.

RESULTS

The evaluable specimens were 671 from the 735 examined; in 64 cases it was not possible to ascertain or to exclude UCS involvement. Invasion of the UCS was found in 59 cases (8.8%). Median follow-up was 59.0 months (range 0-216). Tumours invading the UCS were usually symptomatic, with high nuclear grade and predominantly high stage. At univariate analysis the 5 year overall and cause-specific survival rates of tumours invading the UCS were significantly lower when compared to those without UCS invasion (42.8% versus 60.8% and 45.5% versus 64.7%, respectively). When groups were stratified, according to the pT category, the 5-year cause-specific survival rate was only significantly different for the pT2 category (33.3% versus 76.9%). At the multivariate analysis TNM staging, symptoms at diagnosis and tumour grade were the only independent prognostic factors.

CONCLUSION

The invasion of the UCS by RCC is unusual, particularly in small tumours. UCS involvement does not represent an independent prognostic factor. However, in organ-confined tumours (i.e. pT2) UCS involvement has an influence on the prognosis and should be taken into account when planning adjuvant treatments and follow-up.

Local manipulation of nuclear spin in a semiconductor quantum well

The shaping of nuclear spin polarization profiles and the induction of nuclear resonances are demonstrated within a parabolic quantum well using an externally applied gate voltage. Voltage control of the electron and hole wave functions results in nanometer-scale sheets of polarized nuclei positioned along the growth direction of the well. Applying rf voltages across the gates induces resonant spin transitions of selected isotopes. This depolarizing effect depends strongly on the separation of electrons and holes, suggesting that a highly localized mechanism accounts for the observed behavior.