Probing molecular dynamics at the nanoscale via an individual paramagnetic center

Understanding the dynamics of molecules adsorbed to surfaces or confined to small volumes is a matter of increasing scientific and technological importance. Here, we demonstrate a pulse protocol using individual paramagnetic nitrogen vacancy (NV) centers in diamond to observe the time evolution of 1H spins from organic molecules located a few nanometers from the diamond surface. The protocol records temporal correlations among the interacting 1H spins, and thus is sensitive to the local system dynamics via its impact on the nuclear spin relaxation and interaction with the NV. We are able to gather information on the nanoscale rotational and translational diffusion dynamics by carefully analyzing the time dependence of the NMR signal. Applying this technique to various liquid and solid samples, we find evidence that liquid samples form a semi-solid layer of 1.5 nm thickness on the surface of diamond, where translational diffusion is suppressed while rotational diffusion remains present. Extensions of the present technique could be adapted to highlight the chemical composition of molecules tethered to the diamond surface or to investigate thermally or chemically activated dynamical processes such as molecular folding

Coexistence of bulk and surface states probed by Shubnikov-de Haas oscillations in Bi2_2Se3_3 with high charge-carrier density

Topological insulators are ideally represented as having an insulating bulk with topologically protected, spin-textured surface states. However, it is increasingly becoming clear that these surface transport channels can be accompanied by a finite conducting bulk, as well as additional topologically trivial surface states. To investigate these parallel conduction transport channels, we studied Shubnikov-de Haas oscillations in Bi$_2$Se$_3$ thin films, in high magnetic fields up to 30 T so as to access channels with a lower mobility. We identify a clear Zeeman-split bulk contribution to the oscillations from a comparison between the charge-carrier densities extracted from the magnetoresistance and the oscillations. Furthermore, our analyses indicate the presence of a two-dimensional state and signatures of additional states the origin of which cannot be conclusively determined. Our findings underpin the necessity of theoretical studies on the origin of and the interplay between these parallel conduction channels for a careful analysis of the material's performance.Comment: Manuscript including supplemental materia

Collisional and thermal ionization of sodium Rydberg atoms I. Experiment for nS and nD atoms with n=8-20

Collisional and thermal ionization of sodium nS and nD Rydberg atoms with n=8-20 has been studied. The experiments were performed using a two-step pulsed laser excitation in an effusive atomic beam at atom density of about 2 10^{10} cm^{-3}. Molecular and atomic ions from associative, Penning, and thermal ionization processes were detected. It has been found that the atomic ions were created mainly due to photoionization of Rydberg atoms by photons of blackbody radiation at the ambient temperature of 300K. Blackbody ionization rates and effective lifetimes of Rydberg states of interest were determined. The molecular ions were found to be from associative ionization in Na(nL)+Na(3S) collisions. Rate constants of associative ionization have been measured using an original method based on relative measurements of Na_{2}^{+} and Na^{+} ion signals.Comment: 23 pages, 10 figure

In Situ Muscle Power Differs Without Varying In Vitro Mechanical Properties in Two Insect Leg Muscles Innervated by the Same Motor Neuron

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different

Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO3

Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of magnetic and orbital-ordering below the metal-insulator transition in NdNiO3. The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2) reflection and the observed azimuthal angle and polarization dependence originates from a non collinear magnetic structure. The absence of an orbital signal and the non collinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.Comment: 10 pages, 4 figures, Physical Review B rapid communication, to be publishe

Platelet-activating factor: an inflammatory mediator in the acute phase of allergic conjunctivitis in a guinea-pig model

The role of platelet-activating factor (PAF) as a mediator of increased conjunctival vascular permeability was investigated in a guinea-pig model of immediate hypersensitivity. Vascular permeability of the conjunctiva was determined by measuring the albumin content in lavage fluid (LF) after topical challenge with either PAF or ovalbumin. PAF produced a dose-dependent increase of the vascular permeability within minutes. Topical pretreatment with levocabastine, a potent histamine H1-antagonist demonstrated no effect towards the vascular permeability in response to PAF provocation. Pretreatment with eyedrops containing the specific PAF antagonist BN 52021 (1%) showed a significant inhibition of the vascular permeability (60.2%) and the clinical score (27.5%) after PAF challenge. In sensitized guinea-pigs, levocabastine showed a marked inhibition of both the vascular permeability (80.5%) and the clinical score (70%) after topical challenge with ovalbumin. BN 2021, although to a lesser extent, showed a similar effect towards the vascular permeability (26.8%) and the clinical score (28%) after antigen provocation. When BN 52021 and levocabastine were administered in combination, the vascular permeability was significantly decreased after antigen challenge in comparison with eyes pretreated with levocabastine alone. These results indicate that PAF plays a role in the acute phase of allergic conjunctivitis in the guinea-pig

The clinical relevance of bifid and trifid mandibular canals

Item does not contain fulltextBACKGROUND: Bifid mandibular canals (BMC) and trifid mandibular canals (TMC) are variations on the normal anatomy with incidences ranging from 0.08% to 65.0%. Such aberrations have an important clinical impact. For example, an extra mandibular canal may explain inadequate anesthesia, especially when two mandibular foramina are involved. Furthermore, during mandibular surgery, a second, or even third, neurovascular bundle may be damaged causing paresthesia, neuroma development, or bleeding. CASE REPORT: Two cases are presented in this article. One patient had a BMC on both sites, and the other patient had a TMC on one site and a BMC on the other site. DISCUSSION: Initial screening for the presence of a BMC or TMC can be executed by conventional panoramic radiography. BMCs or TMCs are diagnosed, before executing mandibular surgery; additional CBCT scanning is indicated.1 maart 201

Accelerated growth of orbital schwannomas during pregnancy does not correlate with sex hormone- or growth factor receptor status

Purpose: Until now, three cases of growth of an orbital schwannoma during pregnancy have been published. We aim to provide additional insight in the effect of pregnancy on orbital schwannomas. Methods: We present two additional cases of accelerated growth of orbital schwannomas during pregnancy and investigate receptor expression profiles for estrogen, progesterone, androgen, VEGF, EGF, FGF, PDGF-Rβ and ki-67 in the two pregnant cases and six non-pregnant cases. Results: Case 1: A 26-year-old woman developed unilateral exophthalmos during pregnancy, with normal visual acuity and ocular motility. During a subsequent pregnancy, again the exophthalmos progressed. MRI showed a mass suggestive of schwannoma. After delivery, resection of the lesion was performed through an anterior approach. Pathology confirmed schwannoma. The expression profile was positive for estrogen- and FG

Single-photon-emitting optical centers in diamond fabricated upon Sn implantation

The fabrication of luminescent defects in single-crystal diamond upon Sn implantation and annealing is reported. The relevant spectral features of the optical centers (emission peaks at 593.5 nm, 620.3 nm, 630.7 nm and 646.7 nm) are attributed to Sn-related defects through the correlation of their photoluminescence (PL) intensity with the implantation fluence. Single Sn-related defects were identified and characterized through the acquisition of their second-order auto-correlation emission functions, by means of Hanbury-Brown-Twiss interferometry. The investigation of their single-photon emission regime as a function of excitation laser power revealed that Sn-related defects are based on three-level systems with a 6 ns radiative decay lifetime. In a fraction of the studied centers, the observation of a blinking PL emission is indicative of the existence of a dark state. Furthermore, absorption dependence from the polarization of the excitation radiation with about 45 percent contrast was measured. This work shed light on the existence of a new optical center associated with a group-IV impurity in diamond, with similar photo-physical properties to the already well-known Si-V and Ge-V emitters, thus providing results of interest from both the fundamental and applicative points of view.Comment: 10 pages, 4 figure

Permeability of blood-tear barrier to fluorescein and albumin after application of platelet-activating factor to the eye of the guinea pig

One of the inflammatory responses of the eye to local application of platelet-activating factor (PAF) is oedema of the conjunctiva, caused by extravasation of plasma. Aim of the study was to investigate if fluorescein would leak from the blood into the tears together with plasma protein after application of PAF to the eye. Fluorescein was given intraperitoneally 30 min prior to application of 25 μl of 0.1% solution of PAF. Thirty min after PAF the tear film was collected by washing the surface of the eye with 25 μl of phosphate buffered saline (PBS). Fluorescein in eye washings and in plasma was measured by fluorophotometry and albumin by immunodiffusion. Both fluorescein and albumin appeared in a related fashion in tears, being absent in washings of placebo-treated control eyes. Extravasation of fluorescein can be used as a measure for plasma leakage in the conjunctiva with the advantage over the Evans Blue method that the former is a non-invasive method