Single-Photon Emission Mediated by Single-Electron Tunneling in Plasmonic Nanojunctions.

Recent scanning tunneling microscopy (STM) experiments reported single-molecule fluorescence induced by tunneling currents in the nanoplasmonic cavity formed by the STM tip and the substrate. The electric field of the cavity mode couples with the current-induced charge fluctuations of the molecule, allowing the excitation of photons. We investigate theoretically this system for the experimentally relevant limit of large damping rate κ for the cavity mode and arbitrary coupling strength to a single-electronic level. We find that for bias voltages close to the first inelastic threshold of photon emission, the emitted light displays antibunching behavior with vanishing second-order photon correlation function. At the same time, the current and the intensity of emitted light display Franck-Condon steps at multiples of the cavity frequency ω_{c} with a width controlled by κ rather than the temperature T. For large bias voltages, we predict strong photon bunching of the order of κ/Γ where Γ is the electronic tunneling rate. Our theory thus predicts that strong coupling to a single level allows current-driven nonclassical light emission.

Ambient and at-the-ear occupational noise exposure and serum lipid levels.

OBJECTIVES: Occupational and residential noise exposure has been related to increased risk of cardiovascular disease. Alteration of serum lipid levels has been proposed as a possible causal pathway. The objective of this study was to investigate the relation between ambient and at-the-ear occupational noise exposure and serum levels of total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, and triglycerides when accounting for well-established predictors of lipid levels. METHODS: This cross-sectional study included 424 industrial workers and 84 financial workers to obtain contrast in noise exposure levels. They provided a serum sample and wore portable dosimeters that every 5-s recorded ambient noise exposure levels during a 24-h period. We extracted measurements obtained during work and calculated the full-shift mean ambient noise level. For 331 workers who kept a diary on the use of a hearing protection device (HPD), we subtracted 10 dB from every noise recording obtained during HPD use and estimated the mean full-shift noise exposure level at the ear. RESULTS: Mean ambient noise level was 79.9 dB (A) [range 55.0-98.9] and the mean estimated level at the ear 77.8 dB (A) [range 55.0-94.2]. Ambient and at-the-ear noise levels were strongly associated with increasing levels of triglycerides, cholesterol-HDL ratio, and decreasing levels of HDL-cholesterol, but only in unadjusted analyses that did not account for HPD use and other risk factors. CONCLUSION: No associations between ambient or at-the-ear occupational noise exposure and serum lipid levels were observed. This indicates that a causal pathway between occupational and residential noise exposure and cardiovascular disease does not include alteration of lipid levels.

Controlling single-molecule junction conductance by molecular interactions.

For the rational design of single-molecular electronic devices, it is essential to understand environmental effects on the electronic properties of a working molecule. Here we investigate the impact of molecular interactions on the single-molecule conductance by accurately positioning individual molecules on the electrode. To achieve reproducible and precise conductivity measurements, we utilize relatively weak π-bonding between a phenoxy molecule and a STM-tip to form and cleave one contact to the molecule. The anchoring to the other electrode is kept stable using a chalcogen atom with strong bonding to a Cu(110) substrate. These non-destructive measurements permit us to investigate the variation in single-molecule conductance under different but controlled environmental conditions. Combined with density functional theory calculations, we clarify the role of the electrostatic field in the environmental effect that influences the molecular level alignment.

On the mechanical and electronic properties of thiolated gold nanocrystals.

We present a quantitative exploration, combining experiment and simulation, of the mechanical and electronic properties, as well as the modifications induced by an alkylthiolated coating, at the single nanoparticle (NP) level. We determined the response of the NPs to external pressure in a controlled manner using an atomic force microscope tip. We found a strong reduction in their Young's modulus, as compared to bulk gold, and a significant influence of strain on the electronic properties of the alkylthiolated NPs. Electron transport measurements of tiny molecular junctions (NP/alkylthiol/CAFM tip) show that the effective tunnelling barrier through the adsorbed monolayer strongly decreases by increasing the applied load, which translates in a remarkable and unprecedented increase in the tunnel current. These observations are successfully explained using simulations based on the finite element analysis (FEA) and first-principles calculations that permit one to consider the coupling between the mechanical response of the system and the electric dipole variations at the interface.

H-atom relay reactions in real space.

Hydrogen bonds are the path through which protons and hydrogen atoms can be transferred between molecules. The relay mechanism, in which H-atom transfer occurs in a sequential fashion along hydrogen bonds, plays an essential role in many functional compounds. Here we use the scanning tunnelling microscope to construct and operate a test-bed for real-space observation of H-atom relay reactions at a single-molecule level. We demonstrate that the transfer of H-atoms along hydrogen-bonded chains assembled on a Cu(110) surface is controllable and reversible, and is triggered by excitation of molecular vibrations induced by inelastic tunnelling electrons. The experimental findings are rationalized by ab initio calculations for adsorption geometry, active vibrational modes and reaction pathway, to reach a detailed microscopic picture of the elementary processes.

Engineering negative differential conductance with the Cu(111) surface state.

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states.

Exploring the tilt-angle dependence of electron tunneling across molecular junctions of self-assembled alkanethiols.

Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current-voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect.

Controlled contact to a C60 molecule.

The tip of a low-temperature scanning tunneling microscope is approached towards a C60 molecule adsorbed at a pentagon-hexagon bond on Cu(100) to form a tip-molecule contact. The conductance rapidly increases to approximately 0.25 conductance quanta in the transition region from tunneling to contact. Ab-initio calculations within density functional theory and nonequilibrium Green's function techniques explain the experimental data in terms of the conductance of an essentially undeformed C60. The conductance in the transition region is affected by structural fluctuations which modulate the tip-molecule distance.

[Heavy white coats are not the cause of physicians' headaches and shoulder pain]. / Tunge kitler er ikke årsag til laegernes hovedpine og nakkemyoser.

The weight of doctors' white coats was examined and correlated to the degree of headache and muscle pain in the shoulders. The coat weight of doctors was 1.5 kg (1.1 kg-1.9 kg) (median with 25%-75% in parenthesis). The highest weight was found in the coats of young physicians 2.0 kg (1.7 kg-2.2 kg), which was higher than those of young surgeons. No correlation was seen in the degree of headache and muscle pain in the shoulders. With the long walking distances in hospitals, it would seem that internal medicine is not only an intellectually, but also a physically, demanding job.

Pharmacological aspects of N-acetyl-5-methoxytryptamine (melatonin) and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (pinoline) as antioxidants: reduction of oxidative damage in brain region homogenates.

Oxygen consumption is a necessity for all aerobic organisms, but oxygen is also a toxic molecule that leads to the generation of free radicals. The brain consumes a high percentage of the oxygen inhaled (18.5%), and it contains large amounts of unsaturated fatty acids, which makes it highly susceptible to lipid peroxidation. Melatonin (N-acetyl-5-methoxytryptamine), the main secretory product of the pineal gland, is a free radical scavenger that was found to protect against lipid peroxidation in many experimental models. Another compound found in the pineal gland is pinoline (6-methoxy-1,2,3,4-tetrahydro-beta-carboline). Pinoline is structurally related to melatonin. Evidence suggests that pinoline may have an antioxidant capacity similar to that of melatonin. In this study, the ability of pinoline to protect against H2O2-induced lipid peroxidation of different rat brain homogenates (frontal cortex, striatum, cerebellum, hippocampus, and hypothalamus) was investigated. The degree of lipid peroxidation was assessed by estimating the levels of thiobarbituric acid reactive substances, malondialdehyde (MDA) and 4-hydroxyalkenals (4-HDA). Pinoline's antioxidant capacity was compared with that of melatonin. Both melatonin and pinoline reduced the level of MDA and 4-HDA in a dose-dependent manner in all brain regions tested. To compare the antioxidant capacities, percent-inhibition curves were created, and the IC50 values were calculated. The IC50 values for melatonin were higher in all brain regions than were those for pinoline. The IC50 values for melatonin in the five different brain regions ranged from 0.16 mM-0.66 mM, and for pinoline, they ranged from 0.04 mM-0.13 mM. The possibility of synergistic interactions between melatonin and pinoline were also determined using the method of Berenbaum. Little evidence for either synergistic, additive, or antagonistic interactions between melatonin and pinoline was found.

Chronic daily headache: is "cervicogenic headache" one subgroup?

"Chronic daily headache" should not include cervicogenic headache, which in its typical form is a unilateral headache that can be precipitated mechanically; in other words, probably an organic disorder. Chronic daily headache as such should not be included in the IHS classification.

Atrial natriuretic peptide-LI following subarachnoid haemorrhage in man.

Atrial natriuretic peptide-like immunoreactivity (ANP-LI) was measured in plasma from the external jugular vein (EJV) in the postoperative course of 11 patients with aneurysmal subarachnoid haemorrhage. Samples were taken on day, 1, 2, 3, 5, 7 and 9 after operation and ANP-LI levels were determined using radioimmunoassay. Ten healthy volunteers were investigated with one EJV plasma sample. Comparing the whole group of SAH patients with the control group, no significant differences in ANP-LI levels were found. In one patient very high ANP-LI levels were found together with high mean plasma sodium levels and high urine sodium excretion. This suggests that there is no general correlation between plasma ANP-LI and SAH; in occasional patients such a correlation may be secondary to changes in plasma sodium levels.

Behavioural treatment of scratching in patients with atopic dermatitis.

A behavioural method of habit reversal, in combination with a hydrocortisone cream, was compared with the use of cream alone in the treatment of 17 patients with atopic dermatitis. The patients were assigned randomly to two groups, one of which received the combination treatment and the other regular ointment treatment. The patients' skin status was assessed before and after treatment, and the patients recorded their scratching during the study. Both groups improved, but the group which received habit-reversal therapy improved significantly more. A strong correlation was found between reduction in scratching and improvement in skin status.