Amplified spontaneous emission in polymer-CdSe/ZnS-nanocrystal DFB structures produced by the holographic method.

Amplified spontaneous emission (ASE) is demonstrated in volume-distributed feedback (DFB) structures, formed by colloidal CdSe/ZnS nanocrystals and ZrO2 nanoparticles (NPs) in a polymer matrix. Periodic redistribution of the NPs in an organic matrix was carried out by holographic photopolymerization in a specially developed light-sensitive nanocomposite. The composite consists of two acrylate monomers and two types of inorganic NPs. The NPs provide for the formation of two co-phased gratings-a refractive index grating and an optical gain (losses) grating. The core-shell CdSe/ZnS nanocrystals are used as a gain medium, while ZrO2 NPs create the refractive index grating and enhance the distributed feedback. The period of the volume structure provides the feedback for lasing at the wavelength lambda(las) of about 575 nm in the second diffraction order. In contrast to known laser systems based on volume DFB cavities, in which the different components of the formulation provide optical gain and feedback, in our case the inorganic NPs serve as an emitting material and can provide simultaneously for feedback. By pumping of DFB structures by a titanium-sapphire laser (lambda(pump) = 400 nm, pulse duration of 120 fs) normal to the sample plane, the appearance of a sharp stimulated emission along the grating-vector direction is observed. Output intensity of ASE as a function of the pump energy shows a threshold behavior and full width at half-maximum (FWHM) of the ASE spectral band decreases from 33 to 12 nm.

The durability of silicone versus latex mock arteries.

Latex mock arteries used in medical device testing allow researchers to evaluate mechanical characteristics of intravascular medical products without using animal or human clinical studies for this data. Such intravascular situations include determining properties such as drag and steerability of catheters, recoil of vascular stents, and clinician training. In fatigue testing, the latex mock arteries are used to receive deployed products and are then repeatedly pressurized at biologically relevant pressures to determine the long term durability of the product. By matching dimensions and pressure-volume relationships (compliance) of these latex tubes, researchers have a reliable means to evaluate and predict product lifetimes. The problem with latex mock arteries is two-fold: First, they are opaque so the product inside the artery cannot be seen during evaluation of the integrity of the product or during clinical training sessions. Second, latex tubes fatigue; therefore, the loading that they place on the internalized products varies with time. During long term durability studies, latex tubes may have to be replaced as often as every 100 million cycles. This can be problematic with products that are difficult to redeploy. We have developed a clear silicone mock artery system that allows us to fabricate three-dimensional objects, including tubes with precise geometric and mechanical properties. Our evaluations show that the mock arteries can be stressed up to 400 million cycles with little or no change in mechanical properties. We are in the process of continuing evaluations to determine long term durability.

The high frequency testing of vascular grafts and vascular stents: influence of sample dimensions on maximum allowable frequency.

There are over four dozen companies developing new products for the lucrative vascular graft and vascular stent markets. We have been studying the procedures used to pre-test vascular grafts, vascular stents, and mock arteries into which vascular stents are placed, so that appropriate high frequency durability/fatigue studies can be done in as short a time as possible, but also in a manner in which the data are highly reliable and dependable. In the past, we have evaluated the testing of the natural frequency response of the grafts, mock arteries, and stents in order to determine the frequencies that can be used for long-term life testing. In this paper, we present experiments that evaluate how product geometry affects product frequency response at various loading pressures. Results show that changing the dimensions of the device to be tested such that less fluid has to be injected (in the case of hydrodynamically driven experiments) results in the ability to test these products at a higher frequency.

Clinical digoxin toxicity in the aged in association with co-administered verapamil. A report of two cases and review of the literature.

Digoxin toxicity occurs more commonly in aged than younger individuals. Cardioactive drugs such as quinidine effect digoxin pharmacokinetics so as to increase the potential for digoxin toxicity. The calcium-channel antagonists have become extensively used for cardiac disorders and are often co-administered with digoxin. Despite documented calcium-channel antagonist interactions with digoxin, clinically significant digoxin toxicity associated with their concurrent use is apparently unusual. Two elderly patients receiving digoxin and verapamil simultaneously are presented to demonstrate the clinical importance and potential danger of the concomitant use of these drugs.