Enhanced infrared transmission through subwavelength coaxial metallic arrays

We report the observation of enhanced near-infrared transmission through arrays of subwavelength coaxial metallic structures compared with that through comparable diameter hole arrays as a result of localized electromagnetic modes supported by the complex coaxial unit cell. Polarization and angle-dependent transmission measurements clearly demonstrate the coupling between this localized mode and delocalized surface plasmon modes. A generalized, multiple discrete states Fano line shape provides a good fit to the experimental results.     

Adaptive control of vowel formant frequency: evidence from real-time formant manipulation

Auditory feedback during speech production is known to play a role in speech sound acquisition and is also important for the maintenance of accurate articulation. In two studies the first formant (F1) of monosyllabic consonant-vowel-consonant words (CVCs) was shifted electronically and fed back to the participant very quickly so that participants perceived the modified speech as their own productions. When feedback was shifted up (experiment 1 and 2) or down (experiment 1) participants compensated by producing F1 in the opposite frequency direction from baseline. The threshold size of manipulation that initiated a compensation in F1 was usually greater than 60 Hz. When normal feedback was returned, F1 did not return immediately to baseline but showed an exponential deadaptation pattern. Experiment 1 showed that this effect was not influenced by the direction of the F1 shift, with both raising and lowering of F1 exhibiting the same effects. Experiment 2 showed that manipulating the number of trials that F1 was held at the maximum shift in frequency (0, 15, 45 trials) did not influence the recovery from adaptation. There was a correlation between the lag-one autocorrelation of trial-to-trial changes in F1 in the baseline recordings and the magnitude of compensation. Some participants therefore appeared to more actively stabilize their productions from trial-to-trial. The results provide insight into the perceptual control of speech and the representations that govern sensorimotor coordination.     

The Cellular Interactions of PEGylated Gold Nanoparticles: Effect of PEGylation on Cellular Uptake and Cytotoxicity

Poly(ethylene glycol) (PEG) is frequently used to coat various medical nanoparticles (NPs). As PEG is known to minimize NP interactions with biological specimens, the question remains whether PEGylated NPs are intrinsically less toxic or whether this is caused by reduced NP uptake. In the present work, the effect of gold NP PEGylation on uptake by three cell types is compared and evaluated the effect on cell viability, oxidative stress, cell morphology, and functionality using a multiparametric methodology. The data reveal that PEGylation affects cellular NP uptake in a cell‐type‐dependent manner and influences toxicity by different mechanisms. At similar intracellular NP numbers, PEGylated NPs are found to yield higher levels of cell death, mostly by induction of oxidative stress. These findings reveal that PEGylation significantly reduces NP uptake, but that at similar functional (= cell‐associated) NP levels, non‐PEGylated NPs are better tolerated by the cells.     

A simple method to measure 13CH2 heteronuclear dipolar cross-correlation spectral densities

Here, we report a method to simultaneously determine CH2 cross-correlation spectral densities and T1 relaxation times in the laboratory and rotating frames. To accomplish this, we have employed an indirect approach that is based on measurement of differences in relaxation rates acquired with and without cross-correlation terms. The new method, which can be employed using multidimensional NMR and standard relaxation pulse sequences, is validated experimentally by investigation of a selectively 13C-enriched hexadecapeptide and the uniformly 13C-enriched immunoglobulin-binding domain of streptococcal protein G (GB1). Use of this approach makes determination of CH2 cross-correlation spectral densities in uniformly 13C-enriched proteins now routine and provides novel information concerning their internal motions.     

Continuous‐scan capability at SSRL and applications to X‐ray diffraction

Typical X‐ray diffraction measurements are made by moving a detector to discrete positions in space and then measuring the signal at each stationary position. This step‐scanning method can be time‐consuming, and may induce vibrations in the measurement system when the motors are accelerated and decelerated at each position. Furthermore, diffraction information between the data points may be missed unless a fine step‐scanning is used, which further increases the total measurement time. To utilize beam time efficiently, the motor acceleration and deceleration time should be minimized, and the signal‐to‐noise ratio should be maximized. To accomplish this, an integrated continuous‐scan system was developed at the Stanford Synchrotron Radiation Lightsource (SSRL). The continuous‐scan system uses an in‐house integrated motor controller system and counter/timer electronics. SPEC software is used to control both the hardware and data acquisition systems. The time efficiency and repeatability of the continuous‐scan system were tested using X‐ray diffraction from a ZnO powder and compared with the step‐scan technique. Advantages and limitations of the continuous‐scan system and a demonstration of variable‐velocity continuous scan are discussed.     

Quantum Emulation of Extreme Non‐Equilibrium Phenomena with Trapped Atoms

Ultracold atomic physics experiments offer a nearly ideal context for the investigation of quantum systems far from equilibrium. We describe three related emerging directions of research into extreme non‐equilibrium phenomena in atom traps: quantum emulation of ultrafast atom‐light interactions, coherent phasonic spectroscopy in tunable quasicrystals, and realization of Floquet matter in strongly‐driven lattice systems. We show that all three should enable quantum emulation in parameter regimes inaccessible in solid‐state experiments, facilitating a complementary approach to open problems in non‐equilibrium condensed matter.     

Electronic structure of V in NaMgAl(ox)3·9H2O probed by Fourier transform spectroscopy

High-resolution Fourier transform absorption and luminescence spectroscopy reveal axial and rhombic zero-field splittings of the spin-forbidden electronic origins of V³⁺ in NaMgAl(ox)₃·9H₂O (ox=oxalate) single crystals below 25 K. The temperature dependence of the integrated absorption of the split features display behavior consistent with a Boltzmann distribution within the zero-field split ³Â₂ ground state of V³⁺. Weak luminescence is observed in the near-IR from the lowest energy spin-forbidden transition with a luminescence lifetime of less than 0.5 μs at 11 K and an estimated quantum efficiency of the order of 10⁻⁵.     

Weak localization of light in superdiffusive random systems

Lévy flights constitute a broad class of random walks that occur in many fields of research, from biology to economy and geophysics. The recent advent of Lévy glasses allows us to study Lévy flights-and the resultant superdiffusion-using light waves. This raises several questions about the influence of interference on superdiffusive transport. Superdiffusive structures have the extraordinary property that all points are connected via direct jumps, which is expected to have a strong impact on interference effects such as weak and strong localization. Here we report on the experimental observation of weak localization in Lévy glasses and compare our results with a recently developed theory for multiple scattering in superdiffusive media. Experimental results are in good agreement with theory and allow us to unveil the light propagation inside a finite-size superdiffusive system.     

An Introduction to Influence Theory: Kinematics and Dynamics

Influence theory is a foundational theory of physics that is not based on traditional empirically defined concepts, such as positions in space and time, mass, energy, or momentum. Instead, the aim is to derive these concepts, and their empirically determined relationships, from a more primitive model. It is postulated that there exist things, which are call particles, that influence one another in a discrete and directed fashion resulting in a partially ordered set of influence events. The problem of consistent quantification of the influence events is considered. Observers are modeled as particle chains (observer chains) as if an observer were able to track a particle and quantify the influence events that the particle experiences. From these quantified influence events, consistent quantification of the universe of events based on the observer chains is studied. Herein, the kinematics and dynamics of particles from the perspective of influence theory are both reviewed and further developed.     

MRICOM–MRI COntrast Modelling using 2D T1–T2 correlation spectra and relaxation signatures

Image contrast is calculated by inputting experimental 2D T₁–T₂ relaxation spectra into the ODIN software interface. The method involves characterising a magnetic resonance imaging pulse sequence with a “relaxation signature” which describes the sensitivity of the sequence to relaxation and is independent of sample parameters. Maximising (or minimising) the overlap between the experimental 2D T₁–T₂ relaxation spectra and the relaxation signature can then be used to maximise image contrast. The concept is illustrated using relaxation signatures for the echo planar imaging and Turbo spin-echo imaging sequences, together with in-vitro 2D T₁–T₂ spectra for liver and cartilage.