Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes

We introduce the concept of computerized tomographic microscopy in magnetic resonance imaging using the magnetic fields and field gradients from a ferromagnetic probe. We investigate a configuration where a two-dimensional sample is under the influence of a large static polarizing field, a small perpendicular radio-frequency field, and a magnetic field from a ferromagnetic sphere. We demonstrate that, despite the non-uniform and non-linear nature of the fields from a microscopic magnetic sphere, the concepts of computerized tomography can be applied to obtain proper image reconstruction from the original spectral data by sequentially varying the relative sample-sphere angular orientation. The analysis shows that the recent proposal for atomic resolution magnetic resonance imaging of discrete periodic crystal lattice planes using ferromagnetic probes can also be extended to two-dimensional imaging of non-crystalline samples with resolution ranging from micrometer to Angstrom scales.Comment: 9 pages, 11 figure

Nanowire-based very-high-frequency electromechanical resonator

Fabrication and readout of devices with progressively smaller size, ultimately down to the molecular scale, is critical for the development of very-high-frequency nanoelectromechanical systems (NEMS). Nanomaterials, such as carbon nanotubes or nanowires, offer immense prospects as active elements for these applications. We report the fabrication and measurement of a platinum nanowire resonator, 43 nm in diameter and 1.3 µm in length. This device, among the smallest NEMS reported, has a fundamental vibration frequency of 105.3 MHz, with a quality factor of 8500 at 4 K. Its resonant motion is transduced by a technique that is well suited to ultrasmall mechanical structures

Spectroscopic studies of individual plasmon resonant nanoparticles

We present a detailed description of the apparatus and techniques that we have utilized in our experimental study of individual plasmon resonant nanoparticles, along with a brief description of some major results. The apparatus consists of a spectroscopic system combined with a modified darkfield microscope, which enables the user to sequentially select individual resonant nanostructures in the microscopic field of view for spectroscopic study. Plasmon resonant nanostructures scatter light elastically, and typically have very large scattering cross-sections at their resonant optical wavelengths. In general, spectra can be obtained with acquisition times between .1 to 30 seconds, and color images can be captured using consumer digital color cameras. Spheres, tetrahedrons, and pentagonal platelets were fabricated using colloidal chemistry techniques. To produce highly anisotropic structures such as nanorods and "barbells", templates were used. Many of these nanostructures have been individually spectroscopically characterized, and their spectra correlated with their shape and size as determined by transmission electron microscope (TEM). The unique shape, size, composition, and dielectric surroundings of the individual plasmon resonant nanostructures determine their plasmon resonant behavior. We will show how the composition of the substrate on which the particles are immobilized and the dielectric of the surrounding medium have a significant effect on the plasmon resonance of the individual particles

Quantum dot-based multiphoton fluorescent pipettes for targeted neuronal electrophysiology

Targeting visually identified neurons for electrophysiological recording is a fundamental neuroscience technique; however, its potential is hampered by poor visualization of pipette tips in deep brain tissue. We describe quantum dot-coated glass pipettes that provide strong two-photon contrast at deeper penetration depths than those achievable with current methods. We demonstrated the pipettes' utility in targeted patch-clamp recording experiments and single-cell electroporation of identified rat and mouse neurons in vitro and in vivo

Spectroscopic studies of individual plasmon resonant nanoparticles

We present a detailed description of the apparatus and techniques that we have utilized in our experimental study of individual plasmon resonant nanoparticles, along with a brief description of some major results. The apparatus consists of a spectroscopic system combined with a modified darkfield microscope, which enables the user to sequentially select individual resonant nanostructures in the microscopic field of view for spectroscopic study. Plasmon resonant nanostructures scatter light elastically, and typically have very large scattering cross-sections at their resonant optical wavelengths. In general, spectra can be obtained with acquisition times between .1 to 30 seconds, and color images can be captured using consumer digital color cameras. Spheres, tetrahedrons, and pentagonal platelets were fabricated using colloidal chemistry techniques. To produce highly anisotropic structures such as nanorods and "barbells", templates were used. Many of these nanostructures have been individually spectroscopically characterized, and their spectra correlated with their shape and size as determined by transmission electron microscope (TEM). The unique shape, size, composition, and dielectric surroundings of the individual plasmon resonant nanostructures determine their plasmon resonant behavior. We will show how the composition of the substrate on which the particles are immobilized and the dielectric of the surrounding medium have a significant effect on the plasmon resonance of the individual particles

Effects of prolonged head-down bed rest on sympathetic baroreflex control and orthostatic tolerance

Orthostatic intolerance has been described after prolonged bed confinement in several clinical settings. This may impact patients’ quality of life and increase risk of falls. Standing is associated with unloading of baroreceptor activity controlling heart rate (HR) and sympathetic vasomotor discharge assessed by muscle sympathetic nerve activity (MSNA). In the present study we evaluated the changes in baroreceptor response and in orthostatic tolerance induced by controlled long lasting bed rest in healthy volunteers. As part of the European Space Agency Medium-term Bed Rest protocol, eight volunteers (33 ±1yrs) were studied before and after 21-days of -6º head down bed rest (HDBR). Subjects underwent ECG, beat-by-beat blood pressure, respiratory activity and MSNA recordings during 15-minutes of 80 head-up tilt (HUT) followed by a 3-minute –10mmHg stepwise increase of lower body negative pressure, up to pre-syncope. The α index obtained in the low frequency band (0.1 Hz) by cross-spectrum analysis of RR and systolic arterial pressure (SAP) variability quantified the cardiac baroreflex sensitivity. The percentage of MSNA burst occurrence for different diastolic pressure values (grouped in bins of 1 mmHg) was assessed. The slope of the regression line between MSNA Bursts % and diastolic pressure was assumed to represent the gain of sympathetic baroreflex control (sBRS). the subjects orthostatic tolerance was decreased after HDBR(12±0.6min) compared to baseline (21±0.6min). In the supine position HR, SAP and α index were unchanged before and after HDBR. During HUT, HR and SAP were unmodified, α index was lower after (3.4±0.7) compared to before HDBR (6.4±1.0). While supine, sBRS was lower after (-2.9±1.5 %mmHg) compared to before HDBR (-6.0±1.1 %/mmHg). Similarly, during HUT sBRS was lower after HDBR (-2.2±0.6 %/mmHg) compared to before (-4.4±0.4%mmHg). These data suggest that prolonged bed confinement decreased the overall baroreceptor sensitivity.These alterations may be involved in the reduction of orthostatic tolerance

Syncope in a Working-Age Population: Recurrence Risk and Related Risk Factors

Syncope in a worker undertaking risky tasks may result in fatalities for the individual or for third parties. We aimed at assessing the rate of syncope recurrence and the risk factors underlying the likelihood of syncope relapse in a working-age population. A prospective cohort of all patients aged 18\u207b65 years consecutively admitted to the Emergency Department for syncope was enrolled. Risk of syncope relapse was assessed at a six-month, 1-year, and 5-year follow-up. Predictors of syncope recurrence have been evaluated at six months and 1 year from the syncope index by a multivariable logistic regression analysis. 348 patients were enrolled. Risk of syncope relapse was 9.2% at 6 months, 11.8% at 1 year, and 23.4% at 5 years. At 6-month follow-up, predictor of syncope recurrence was 653 prior lifetime syncope episodes. At 1-year, 653 prior lifetime syncope episodes, diabetes mellitus, and anaemia were risk factors for syncope relapse. There was an exceeding risk of recurrence in the first 6 months and a reduced risk of 3.5% per year after the first year. Anaemia, diabetes mellitus, and prior lifetime syncope burden are of importance when giving advice about the resumption of "high risk" jobs following a syncope episode

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio