Photoswitching of Ferroelectric Liquid Crystals Using Unsymmetrical Chiral Thioindigo Dopants: Photoinduced Inversion of the Sign of Spontaneous Polarization

A new unsymmetrical chiral thioindigo dopant 6‐[(R,R)‐2,3‐difluorooct‐1‐yloxy]‐5′‐nitro‐6′‐[(R)‐2‐octyloxy]thioindigo ( 4 ) designed to photoinvert the sign of spontaneous polarization (P_S) in a ferroelectric chiral smectic C (SmC*) liquid crystal was prepared using a synthetic approach previously developed in our laboratory. In this new “ambidextrous” design, the (R)‐2‐octyloxy side‐chain is sterically coupled to the thioindigo core and induces a positive P_S, whereas the (R,R)‐2,3‐difluorooctyloxy side‐chain is decoupled from the core and induces a larger negative P_S. In the trans form, this dopant induces a negative polarization in the SmC host (+)‐4‐(4‐methylhexyloxy)phenyl 4‐decyloxybenzoate ( PhB ). Irradiation of a 1 mol‐% mixture of 4 in PhB at λ = 510 nm caused a sign inversion of P_S, from –0.88 to +0.42 nC cm^–2 at T – T_C = –5 °C, which is consistent with an increase in the polarization power of the coupled 2‐octyloxy/thioindigo unit over that of the 2,3‐difluorooctyloxy unit, due to the increase in transverse dipole moment of the thioindigo core upon trans–cis photoisomerization. The P_S sign inversion was confirmed by a surface‐stabilized ferroelectric liquid crystal photoswitching experiment. Spectroscopic measurements on films of the doped liquid crystal mixtures showed that trans–cis photoisomerization is gradually suppressed with increasing dopant mole fraction, possibly as a result of increased dopant aggregation.     

Power system harmonic resonance-a documented case

A case of power system harmonic resonance that resulted in failure of 13.8 kV switchgear and consequent plant losses is documented. Calculations of the power system natural frequencies are given for various power system configurations of supply reactance, motor reactance, and system shunt capacitance. Sources of harmonic current are identified, methods of measuring harmonic current and voltage levels throughout the system are described, and results of the power system harmonic current and voltage survey are reported. Also described is the corrective action taken to prevent a recurrence of harmonic resonance     

Experimental evaluation of space/frequency/polarization diversityin the indoor wireless channel

A series of experiments that were conducted to evaluate the relative merits of frequency, space, and polarization diversities in indoor portable radio channels at 900 MHz are described. Unmodulated tones were used to probe the channel in a typical university work environment. The statistics of the signal envelopes were analyzed to determine the correlation of the field strengths when the signals are separated in space, frequency or polarization. According to the results presented here, the performance of a narrowband system (<200 kHz) at 900 MHz could greatly benefit from a frequency diversity scheme provided that the separation between the two frequencies is greater than approximately 5 MHz. Similarly, the advantage of space diversity is found significant when the two antennas are spaced by 3/4 wavelength or more. Co-polarized and cross-polarized signals are nearly uncorrelated and their relative field strengths differ by less than 2 dB in most locations     

Immediate adaptation of the dog kidney to acute hypercapnia

Studies were performed to determine whether ammoniagenesis could adapt instantaneously to acidosis in the dog kidney. Following acute respiratory acidosis, renal glutamine extraction rose acutely in dogs with stable renal blood flow but did not change when the renal blood flow fell by more than 25%. Acute hypercapnia immediately increased renal ammonia production in both groups of dogs. The rate of both glutamine extraction and ammonia production in acutely hypercapnic dogs without hemodynamic changes was comparable to the rates observed in dogs with chronic metabolic acidosis. Furthermore, the renal metabolite profile observed in acute hypercapnia was similar to the pattern described in chronic metabolic acidosis, i.e., a marked fall in renal glutamate and alpha-ketoglutarate concentrations and a fivefold increase in malate and oxaloacetate concentrations. In the liver and muscle, acute hypercapnia induced no significant change in glutamine concentration but glutamate and alpha-ketoglutarate concentrations decreased. Our findings demonstrate that the dog kidney can adapt immediately to acidosis but that hemodynamic change may mask this adaptation.     

Quasi-elastic light scattering for intermittent dynamics

Dynamic light-scattering techniques provide noninvasive probes of diverse media such as colloidal suspensions, granular materials, and foams. Traditional analysis relies on the Gaussian properties of the scattering process found in most experimental situations and uses second-order intensity-correlation functions. This approach fails in the presence of, among other things, the collective intermittent dynamics found in systems such as granular materials. By extending the existing formalism and introducing higher-order intensity-correlation functions, we show how to detect and quantify the intrinsic dynamics and switching statistics of intermittent processes. We then explore two systems: (1) an auger-driven granular column for which the granular dynamics are controlled and the formalism is tested and (2) a granular heap whose dynamics are a priori unknown but may, now, be characterized.     

Present and future of simultaneous EEG-fMRI

The brain’s activity can be measured in numerous complementary ways, including electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). The simultaneous acquisition of EEG and fMRI was originally developed to make the localization of the generators of often subtle pathological activity commonly observed in EEG recordings of patients with epilepsy more sensitive and spatially accurate by mapping their hemodynamic correlates. Now, the value of the information provided by simultaneous EEG-fMRI is being evaluated in a clinical context, while in parallel, more sophisticated data analysis techniques, e.g. with electrical source imaging or dynamic causal modeling, have begun to be applied to increase the technique’s sensitivity and allow the study of brain network structure. Beyond its clinically oriented application in epilepsy, simultaneous EEG-fMRI recording has now gained interest as a tool for basic and systems human neuroscience, e.g. the study of neuro-vascular coupling and cognitive studies. In this review, we give an overview over the current use of simultaneous EEG-fMRI, its applications to the study of epilepsy as well as human cognition and systems neuroscience and ongoing and anticipated methodological developments.