Optical clocks based on ultra-narrow three-photon resonances in alkaline earth atoms

A sharp resonance line that appears in three-photon transitions between the $^{1}S_{0}$ and $^{3}P_{0}$ states of alkaline earth and Yb atoms is proposed as an optical frequency standard. This proposal permits the use of the even isotopes, in which the clock transition is narrower than in proposed clocks using the odd isotopes and the energy interval is not affected by external magnetic fields or the polarization of trapping light. The method has the unique feature that the width and rate of the clock transition can be continuously adjusted from the $MHz$ level to sub-$mHz$ without loss of signal amplitude by varying the intensities of the three optical beams. Doppler and recoil effects can be eliminated by proper alignment of the three optical beams or by point confinement in a lattice trap. The three beams can be mixed to produce the optical frequency corresponding to the $^{3}P_{0}$ - $^{1}S_{0}$ clock interval.Comment: 10 pages, 4 figures, submitted to PR

Second harmonic generation from thin slabs in the discrete dipole approach

The nonlinear optical response of thin Si slabs is calculated using a discrete dipole approach. The s-polarized second harmonic response as a function of the angle of incidence appears to be in reasonable agreement with experimental results. The p-polarized SHG shows a high sensitivity for the shape of the polarizability profile

A Dynamic Programming Solution to Bounded Dejittering Problems

We propose a dynamic programming solution to image dejittering problems with bounded displacements and obtain efficient algorithms for the removal of line jitter, line pixel jitter, and pixel jitter.Comment: The final publication is available at link.springer.co

Wear and friction performance of PTFE filled epoxy composites with a high concentration of SiO2 particles

In this work, the tribological performance of PTFE filled SiO2 particles–epoxy composites is investigated. Under a load of 60 N (~140 MPa contact pressure), the optimum content of PTFE lies between 10 and 15 wt%, which yields an ultralow coefficient of friction (CoF) in conjunction with a low wear rate of the composite when dry sliding against bearing steel balls within 1000 m. With 12.5 wt% PTFE in the composite, a CoF around 0.095 and a wear rate as low as 8.4×10−7 mm3/Nm were measured up to a sliding distance of around 2000 m. After 2000 m, eventually the gradual accumulation of the fractured SiO2 particles and back-transferred steel on the worn composite surface leads to a significant increase of CoF. In the steady-state of sliding, smearing of the PTFE particles along the worn surface was observed together with fracturing of the SiO2 particles and cracking of the epoxy matrix. Successive EDS mapping shows the formation and evolution of a PTFE-containing third-body tribolayer on the worn surface of the composite. The thickness of the tribolayer was measured about 20–30 nm on the surface of SiO2 particles after sliding for more than 700 m

Ion-beam-induced bending of freestanding amorphous nanowires: The importance of the substrate material and charging

Ion-beam irradiation offers great flexibility and controllability in the construction of freestanding nanostructures with multiple advanced functionalities. Here, we present and discuss the bending of free-standing nanowires, against, towards, and ultimately parallel to a flux of directional ion irradiation. Bending components both along and perpendicular to the incident ion beam were observed, and the bending behavior was found to depend both on the ion beam scanning strategy and on the conductivity of the supporting substrate. This behavior is explained by an ion-irradiation-related electrostatic interaction. Our findings suggest the prospect of exploiting this technique to engineer 3D nanostructures for advanced applications

Health App Possession Among Smartphone or Tablet Owners in Hong Kong: Population-Based Survey

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A community based intervention program to enhance neighborhood cohesion: The Learning Families Project in Hong Kong

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The role of surface plasmons in the decay of image-potential states on silver surfaces

The combined effect of single-particle and collective surface excitations in the decay of image-potential states on Ag surfaces is investigated, and the origin of the long-standing discrepancy between experimental measurements and previous theoretical predictions for the lifetime of these states is elucidated. Although surface-plasmon excitation had been expected to reduce the image-state lifetime, we demonstrate that the subtle combination of the spatial variation of s-d polarization in Ag and the characteristic non-locality of many-electron interactions near the surface yields surprisingly long image-state lifetimes, in agreement with experiment.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let

A Systematic Comparison of 18F-C-SNAT to Established Radiotracer Imaging Agents for the Detection of Tumor Response to Treatment

PURPOSE: An early readout of tumor response to therapy through measurement of drug or radiation-induced cell death may provide important prognostic indications and improved patient management. It has been shown that the uptake of (18)F-C-SNAT can be used to detect early response to therapy in tumors by positron emission tomography (PET) via a mechanism of caspase-3-triggered nanoaggregation. EXPERIMENTAL DESIGN: Here, we compared the preclinical utility of (18)F-C-SNAT for the detection of drug-induced cell death to clinically evaluated radiotracers, (18)F-FDG, (99m)Tc-Annexin V, and (18)F-ML-10 in tumor cells in culture, and in tumor-bearing mice in vivo. RESULTS: In drug-treated lymphoma cells, (18)F-FDG, (99m)Tc-Annexin V, and (18)F-C-SNAT cell-associated radioactivity correlated well to levels of cell death (R(2) > 0.8; P 0.05). A similar pattern of response was observed in two human NSCLC cell lines following carboplatin treatment. EL-4 tumor uptake of (99m)Tc-Annexin V and (18)F-C-SNAT were increased 1.4- and 2.1-fold, respectively, in drug-treated versus naïve control animals (P < 0.05), although (99m)Tc-Annexin V binding did not correlate to ex vivo TUNEL staining of tissue sections. A differential response was not observed with either (18)F-FDG or (18)F-ML-10. CONCLUSIONS: We have demonstrated here that (18)F-C-SNAT can sensitively detect drug-induced cell death in murine lymphoma and human NSCLC. Despite favorable image contrast obtained with (18)F-C-SNAT, the development of next-generation derivatives, using the same novel and promising uptake mechanism, but displaying improved biodistribution profiles, are warranted for maximum clinical utility

Kinks in the dispersion of strongly correlated electrons

The properties of condensed matter are determined by single-particle and collective excitations and their interactions. These quantum-mechanical excitations are characterized by an energy E and a momentum \hbar k which are related through their dispersion E_k. The coupling of two excitations may lead to abrupt changes (kinks) in the slope of the dispersion. Such kinks thus carry important information about interactions in a many-body system. For example, kinks detected at 40-70 meV below the Fermi level in the electronic dispersion of high-temperature superconductors are taken as evidence for phonon or spin-fluctuation based pairing mechanisms. Kinks in the electronic dispersion at binding energies ranging from 30 to 800 meV are also found in various other metals posing questions about their origins. Here we report a novel, purely electronic mechanism yielding kinks in the electron dispersions. It applies to strongly correlated metals whose spectral function shows well separated Hubbard subbands and central peak as, for example, in transition metal-oxides. The position of the kinks and the energy range of validity of Fermi-liquid (FL) theory is determined solely by the FL renormalization factor and the bare, uncorrelated band structure. Angle-resolved photoemission spectroscopy (ARPES) experiments at binding energies outside the FL regime can thus provide new, previously unexpected information about strongly correlated electronic systems.Comment: 8 pages, 5 figure