246 research outputs found
Antenna-enhanced Optoelectronic Probing of Carbon Nanotubes
We report on the first antenna-enhanced optoelectronic microscopy studies on
nanoscale devices. By coupling the emission and excitation to a scanning
optical antenna, we are able to locally enhance the electroluminescence and
photocurrent along a carbon nanotube device. We show that the emission source
of the electroluminescence can be point-like with a spatial extension below 20
nm. Topographic and antenna-enhanced photocurrent measurements reveal that the
emission takes place at the location of highest local electric field indicating
that the mechanism behind the emission is the radiative decay of excitons
created via impact excitation
Cavity-enhanced Raman Microscopy of Individual Carbon Nanotubes
Raman spectroscopy reveals chemically specific information and provides
label-free insight into the molecular world. However, the signals are
intrinsically weak and call for enhancement techniques. Here, we demonstrate
Purcell enhancement of Raman scattering in a tunable high-finesse microcavity,
and utilize it for molecular diagnostics by combined Raman and absorption
imaging. Studying individual single-wall carbon nanotubes, we identify crucial
structural parameters such as nanotube radius, electronic structure and
extinction cross-section. We observe a 320-times enhanced Raman scattering
spectral density and an effective Purcell factor of 6.2, together with a
collection efficiency of 60%. Potential for significantly higher enhancement,
quantitative signals, inherent spectral filtering and absence of intrinsic
background in cavity-vacuum stimulated Raman scattering render the technique a
promising tool for molecular imaging. Furthermore, cavity-enhanced Raman
transitions involving localized excitons could potentially be used for gaining
quantum control over nanomechanical motion and open a route for molecular
cavity optomechanics
Courtship behaviour in the genus Nomada - antennal grabbing and possible transfer of male secretions
Due to low population densities, copulation in the cuckoo bee genus Nomada has not previously been observed, although a seminal paper by Teng8 and Bergstrom (1977) on the chemomimesis between these parasitic bees and their Andrena or Melilla hosts postulated that secretions from male glands might be sprayed onto females during copulation. Our observations on the initiation and insertion phase of copulation in three species of Nomada now indicate antennal grabbing as a mechanism by which chemicals are transferred between the sexes. Histological studies of the antennae of N. fucata and N. lathburiana reveal antennal modifications associated with cell aggregations that represent glandular cells, and SEM studies revealed numerous excretory canals
Sub-Poissonian statistics of Rydberg-interacting dark-state polaritons
Interfacing light and matter at the quantum level is at the heart of modern
atomic and optical physics and enables new quantum technologies involving the
manipulation of single photons and atoms. A prototypical atom-light interface
is electromagnetically induced transparency, in which quantum interference
gives rise to hybrid states of photons and atoms called dark-state polaritons.
We have observed individual dark-state polaritons as they propagate through an
ultracold atomic gas involving Rydberg states. Strong long-range interactions
between Rydberg atoms give rise to an effective interaction blockade for
dark-state polaritons, which results in large optical nonlinearities and
modified polariton number statistics. The observed statistical fluctuations
drop well below the quantum noise limit indicating that photon correlations
modified by the strong interactions have a significant back-action on the
Rydberg atom statistics.Comment: 7 pages, 4 figure
Pancreatic Polypeptide but Not Other Members of the Neuropeptide Y Family Shows a Moderate Association With Perceived Anxiety in Obese Men
Neuropeptide Y (NPY), peptide tyrosine tyrosine (PYY), and pancreatic polypeptide (PP) are important mediators in the bidirectional communication along the gut-brain-axis. Best known for their role in the regulation of appetite and food intake they are considered to play a crucial role in the development of obesity. Additionally, mounting evidence indicates a regulatory function in anxiety, mood and stress resilience with potential sex differences. In the present study, we examined the associations of NPY, PYY, and PP plasma levels with anxiety, depressiveness and perceived stress in obese patients. We analyzed 144 inpatients (90 female, 54 male, BMI mean: 49.4 kg/m(2)) in a naturalistic treatment setting for obesity and its somatic and mental comorbidities. Fasting blood samples were taken, and patients completed psychometric self-assessment questionnaires (GAD-7, PHQ-9, PSQ-20) within the first week after admission and before discharge. Plasma concentrations of the peptides were measured by ELISA. Women showed significant higher anxiety (GAD-7: 8.13 +/- 5.67 vs. 5.93 +/- 5.42, p = 0.04) and stress scores (PSQ-20: 52.62 +/- 23.5 vs. 41.23 +/- 22.53, p = 0.01) than men. In the longitudinal analysis women with a clinically relevant improvement of anxiety ( \u3e /= 5 points on GAD-7, p \u3c 0.001) also showed significant improvements in depression (PHQ-9: 38%, p = 0.002) and PSQ-20 scores (23%, p = 0.005) while anxiety-improved male patients only improved in the subscale tension of the PSQ-20 (34%, p = 0.02). In men we observed a positive correlation of PP with anxiety scores (GAD-7: r = 0.41, p = 0.007) and with age (r = 0.49, p = 0.001) on admission while NPY negatively correlated with age (r = -0.38, p = 0.01). In contrast, there were no significant associations (p \u3e 0.05) in female subjects in the cross-sectional as well as in the longitudinal analysis. In conclusion, women suffering from morbid obesity showed greater psychological comorbidity and considerable interactions among them. Despite that we solely observed associations of PP with anxiety and age with NPY and PP in men, suggesting a possible influence of sex hormones on the NPY system. However, improvement of anxiety scores did not lead to significant changes in NPY
Synthesis and cryogenic spectroscopy of narrow-diameter single-wall carbon nanotubes
AbstractWe report chemical vapor deposition and cryogenic photoluminescence studies of narrow-diameter single-wall carbon nanotubes. Our systematic study of synthesis parameters identifies means to control the average length, diameter, and areal density of carbon nanotubes grown on silica substrates. Using synthesis conditions that favor the growth of carbon nanotubes with sub-nanometer diameters, we fabricate samples with spatially isolated suspended nanotubes ideally suited for optical studies. Photoluminescence spectroscopy of individual nanotubes reveals two classes: spectrally broad and narrow single-peak emission at the temperature of liquid helium. The latter class with spectral line widths down to the resolution limit of our spectrometer of 40 μeV indicates that exciton coherence in carbon nanotubes can be substantially improved by controlling the growth conditions and utilized in sources of indistinguishable single photons
Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations
A comprehensive study of the electronic properties of monoclinic MoO2 from
both an experimental and a theoretical point of view is presented. We focus on
the investigation of the Fermi body and the band structure using angle resolved
photoemission spectroscopy, de Haas-van Alphen measurements, and electronic
structure calculations. For the latter, the new full-potential augmented
spherical wave (ASW) method has been applied. Very good agreement between the
experimental and theoretical results is found. In particular, all Fermi surface
sheets are correctly identified by all three approaches. Previous controversies
concerning additional hole-like surfaces centered around the Z- and B-point
could be resolved; these surfaces were an artefact of the atomic-sphere
approximation used in the old calculations. Our results underline the
importance of electronic structure calculations for the understanding of MoO2
and the neighbouring rutile-type early transition-metal dioxides. This includes
the low-temperature insulating phases of VO2 and NbO2, which have crystal
structures very similar to that of molybdenum dioxide and display the
well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at
http://www.physik.uni-augsburg.de/~eyert
Measles IgG Antibody Index Correlates with T2 Lesion Load on MRI in Patients with Early Multiple Sclerosis
Background: B cells and humoral immune responses play an important role in the pathogenesis and diagnosis of multiple sclerosis (MS). A characteristic finding in patients with MS is a polyspecific intrathecal B cell response against neurotropic viruses, specifically against measles virus, rubella virus, and varicella zoster virus, also known as an MRZ reaction (MRZR). Here, we correlated from the routine clinical diagnostics individual IgG antibody indices (AIs) of MRZR with magnetic resonance imaging (MRI) findings in patients with first MS diagnosis. Methods/Results: MRZR was determined in 68 patients with a clinically isolated syndrome (CIS) or early relapsing-remitting MS (RRMS). Absolute AI values for measles virus, rubella virus, and varicella zoster virus were correlated with T2 lesion load and gadolinium enhancing lesions on cerebral MRI (cMRI) and cMRI combined with spinal MRI (sMRI). Measles virus AI correlated significantly with T2 lesion load on cMRI (p = 0.0312, Mann-Whitney U test) and the sum of lesions on cMRI and sMRI (p = 0.0413). Varicella zoster virus AI also showed a correlation with T2 lesion load on cMRI but did not reach statistical significance (p = 0.2893). Conclusion: The results confirm MRZR as part of the polyspecific immune reaction in MS with possible prognostic impact on MRI and clinical parameters. Furthermore, the data indicate that intrathecal measles virus IgG production correlates wit
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