Hydrogen-Induced Ultralow Optical Absorption and Mechanical Loss in Amorphous Silicon for Gravitational-Wave Detectors.

The sensitivity of gravitational-wave detectors is limited by the mechanical loss associated with the amorphous coatings of the detectors' mirrors. Amorphous silicon has higher refraction index and lower mechanical loss than current high-index coatings, but its optical absorption at the wavelength used for the detectors is at present large. The addition of hydrogen to the amorphous silicon network reduces both optical absorption and mechanical loss for films prepared under a range of conditions at all measured wavelengths and temperatures, with a particularly large effect on films grown at room temperature. The uptake of hydrogen is greatest in the films grown at room temperature, but still below 1.5 at.% H, which show an ultralow optical absorption (below 10 ppm) measured at 2000 nm for 500-nm-thick films. These results show that hydrogenation is a promising strategy to reduce both optical absorption and mechanical loss in amorphous silicon, and may enable fabrication of mirror coatings for gravitational-wave detectors with improved sensitivity.

Light-driven photoswitching of quinazoline analogues of combretastatin A-4 as an effective approach for targeting skin cancer cells.

A novel quinazoline series of photoswitchable combretastatin A-4 (CA-4) analogues were synthesized and their photochemical properties and antiproliferative activity against A431 epidermoid carcinoma cells were studied. It was found that quinazoline analogues, in contrast to the majority of the known CA-4, exhibit high antiproliferative activity in the E-form as well. Photoswitching of the E-form to the Z-form resulted in a multiple (9-fold) increase in antiproliferative activity. 1H NMR monitoring showed that these compounds are very resistant to UV (λ = 365 nm) or sunlight irradiation and do not undergo photodegradation with a loss of antiproliferative activity that is inherent in heterocyclic analogues of CA-4. Similar photoswitching and an increase in antiproliferative activity are observed on exposure to sunlight. A selected compound (1a-Z51) in sub-micromolar concentrations induced apoptosis in A431 cells, while rad50/ATM/p53 were not involved in cell death. The growth of A431 cells was significantly inhibited after combination treatment with compound 1a-Z51 and chemotherapy drugs (cisplatin or 5-fluorouracil). In summary, the quinazoline analogues of CA-4 represent a promising strategy to achieve a photoswitchable potency for the treatment of cancers, including the development of combination therapies.

High Precision Detection of Change in Intermediate Range Order of Amorphous Zirconia-Doped Tantala Thin Films Due to Annealing.

Understanding the local atomic order in amorphous thin film coatings and how it relates to macroscopic performance factors, such as mechanical loss, provides an important path towards enabling the accelerated discovery and development of improved coatings. High precision x-ray scattering measurements of thin films of amorphous zirconia-doped tantala (ZrO_{2}-Ta_{2}O_{5}) show systematic changes in intermediate range order (IRO) as a function of postdeposition heat treatment (annealing). Atomic modeling captures and explains these changes, and shows that the material has building blocks of metal-centered polyhedra and the effect of annealing is to alter the connections between the polyhedra. The observed changes in IRO are associated with a shift in the ratio of corner-sharing to edge-sharing polyhedra. These changes correlate with changes in mechanical loss upon annealing, and suggest that the mechanical loss can be reduced by developing a material with a designed ratio of corner-sharing to edge-sharing polyhedra.

Point defects in Sc2O3 thin films by ion beam sputtering.

We show that the concentration of oxygen interstitials trapped in Sc2O3 films by ion beam sputtering from metal targets can be controlled by modifying deposition conditions. We have identified point defects in the form of oxygen interstitials that are present in Sc2O3 films, in significantly high concentrations, i.e., ∼10(18) cm(-3). These results show a correlation between the increase of oxygen interstitials and the increase in stress and optical absorption in the films. Sc2O3 films with the lowest stress and optical absorption loss at 1 µm wavelength were obtained when using a low oxygen partial pressure and low beam voltage.

Parathyroid hormone as a modulator of the functional activity of neuron.

The effect of 10-10 M parathyroid hormone (PTH) on Ca2+ levels and cAMP and cGMP contents in peripharyngeal ganglions of the snail Helix pomatia was studied by radioisotope and radioimmune methods; also, chemoreception of GABA was determined in the neuronal membrane. The levels of Ca2+ and cyclic nucleotides were increased in the ganglions. Co-addition of PTH with compounds increasing the levels of Ca2+ and cyclic nucleotides lowered these elevations of the levels of Ca2+ and cyclic nucleotides. Depending on the initial levels of Ca2+ and cyclic nucleotides in the neuron, PTH can direct the fluxes of ions either into or out of the cell and can activate the cyclase or phosphodiesterase systems. PTH decreased the binding of GABA by the ganglions at high GABA concentrations and under conditions which promote increased binding of GABA. These data suggest that PTH has neuroprotective effects and protects the neuronal tissue from inhibition. Thus, PTH can modulate the function of neurons.

Parathyroid hormone enhances calcium current in snail neurones--simulation of the effect by phorbol esters.

Effects of parathyroid hormone substance (PTH) on the voltage-activated calcium current (ICa) were studied on intracellularly perfused neurones of the snail, Helix pomatia, under voltage-clamp conditions. Application of 0.1 nM PTH produced a marked potentiation of the current. The effect developed slowly (60-70 min) and remained after removal of PTH. Potentiation could be observed in most neurones, but varied considerably from cell to cell; in some neurones ICa was increased 2- to 3-fold. Addition of ethylenebis(oxonitrilo)tetraacetate (EGTA, 10 mM) to, or removal of adenosine 5'-triphosphate (ATP, 2 mM) from the intracellular perfusing solution resulted in a suppression or attenuation of the potentiating effect. The effect could be reproduced by the synthetic 1-34 amino acid fragment of PTH. Extracellularly applied protein kinase-C (PK-C) activator phorbol ester phorbol 12-myristate 13-acetate (PMA, 0.1-10 microM) produced a similar slow increase in ICa (up to 1.5- to 2-fold), while its inactive analogue (4 alpha-phorbol ester) had no effect on ICa. The effects of PTH and PMA were not additive. PK-C inhibitors [1-(5-isoquinoline-sulphonyl)-2-methylpiperazine hydrochloride] (H-7, 100 microM) and staurosporine (100 microM) as well as calcium channel antagonists Cd2+, verapamil, nifedipine and nimodipine depressed the effect of PTH. The chloride channel blocker 4,4'-diisothiocyanato-stilbene-2,2'-disulphonic acid (DIDS, 1 mM) did not affect the potentiating action of PTH. Activation of the adenylate cyclase system also potentiated ICa in some neurones, but this effect had a different time course and was additive to the effect of PTH.2=