Efficient integral-equation-based method for accurate analysis of scattering from periodically arranged nanostructures.

A plethora of applications are grounded on the physics of electromagnetic interaction with a periodic arrangement of nanostructures. These range from metamaterials and negative index materials to photonic band-gap structures to surface plasmon polariton optics to nanofrequency selective surfaces. There is therefore a need for rigorous physics based methods that are both accurate and fast to enable rapid design and analysis. Difficulties that need to be overcome to realize such a simulation tool are twofold: (i) at wavelengths in the range 200-1300 nm metals behave as dielectrics with negative real permittivity. Their frequency response must be explicitly accounted for in the simulation. (ii) The computational cost to compute response over a broad band of frequencies is high. This paper develops an integral-equation-based analysis technique that addresses these challenges. This integral equation relies on a periodic layered medium formulation. The Green's dyad for this formulation is derived, and separated into a superposition of two contributions: direct and reflected components. The means to accelerate the computation of the Green's dyad and the evaluation of inner products is prescribed. The proposed technique is validated extensively against available analytical data for hypothetical materials as well as silver. It is shown that this solver can accurately predict the enhanced transmission from perforated silver films for several configurations. While the application domain in this paper is the study of enhanced transmission in perforated silver films, the method presented herein is sufficiently general and can be applied to several other application domains with little or no change.

Protein-linked isoprenoid lipids in dexamethasone-treated human lymphoid lines in culture.

Accumulation of isoprenoids was studied in two cell lines derived from acute T-cell leukemia: CEM-C7 cells, whose growth is inhibited by the glucocorticoid dexamethasone, and CEM-C1 cells, which are resistant to this steroid. Isoprenoids were measured by growing the cells in serum-free medium in the presence of lovastatin, which blocks synthesis of mevalonate, and then labeling with exogenous [3H]mevalonolactone. In both cell lines, isoprenoids associated with proteins were detected in cytoplasm, nucleus, and chromatin, and in the chromatin residue that remains after extraction of histone and nonhistone proteins. Differences in labeling were detected after treatment with dexamethasone in the CEM-C7 line, showing a decrease in the cytoplasmic fraction with a corresponding increase in both the nuclear and chromatin fractions as compared with untreated cells. No change was seen in the CEM-C1 line. In both cell lines, 25-30% of the incorporated label was released by treatment with acid or alkali. However, the majority of the label required treatment with methyl iodide for the release of organic-soluble tritiated products. After extraction with chloroform, the lipid fractions contained farnesol, geraniol, dolichols, and possibly nerolidol.

Effects of compound RU38486 on growth and lipid biosynthesis in glucocorticoid sensitive human leukemia line CEM-C7.

Glucocorticoid sensitive human lymphoblastoid cells CEM-C7 were examined for the effects of antiglucocorticoid RU38486 on the prevention of early dexamethasone-induced changes, including reduced cell growth, cell shrinkage and fragmentation, decrease in cell plating efficiency and incorporation of acetate into cellular lipids. When RU38486 was added no later than 24 hours after the addition of dexamethasone, it prevented the inhibition of [14C]acetate incorporation into nonsaponifiable lipids, partly reversed the decrease in plating efficiency and reduced cell fragmentation. In addition, the accumulation of dolichols in the nuclei of dexamethasone-treated cells was abolished by RU38486. These results indicate that glucocorticoid-induced changes in cellular lipids are receptor dependent and may be linked to the initiation of the apoptotic cascade.

Developmental patterns in rat brain of phosphatidylinositol synthetic enzymes and phosphatidylinositol transfer protein.

Phosphatidylinositol synthetic and intermembrane transfer activities were studied in rat in the developing whole brain and isolated cerebellum. Specific activities of CTP:phosphatidate cytidylyltransferase and CDPdiacylglycerol:inositol phosphatidyltransferase were found to have similar developmental patterns. Levels of phosphatidyltransferase seen in fetal animals (whole brain only) and neonatal (whole brain and cerebellum) were maintained through approximately postnatal day 15, peaked at day 28, and then declined to somewhat higher than fetal levels at day 60. Cytidylyltransferase activity varied from the phosphatidylinositol synthesizing enzyme in that specific activity continued to increase up to day 60. Whole brain phosphatidylinositol transfer specific activity showed a sharp peak at postnatal day 9 after which activity was maintained at or above the fetal levels to day 60. Cerebellum phosphatidylinositol transfer specific activity had a similar peak which was delayed 7-10 days compared to the whole brain. Phosphatidylinositol transfer protein was also determined immunologically: whole brain levels increased dramatically from fetal day 16 to 18 and then remained relatively constant, while cerebellum levels (measured from postnatal day 7) displayed a variable profile between days 7 and 28. The developmental pattern of CTP:phosphatidate cytidylyltransferase in rat brain is reported here for the first time.

Thiophosphoester analogs of phosphatidic acids: spectrophotometric substrates for phosphomonoesterases.

Thiophosphoester analogs of dioctanoyl and didecanoyl phosphatidic acids were synthesized for use as substrates in spectrophotometric assays. These substrates are easily dispersable in aqueous media and release thiodiacylglycerols after phosphomonoesterase catalyzed hydrolysis. The free sulfhydryl of these thiodiacylglycerols reacts with the colorimetric reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), allowing the reaction to be followed. These analogs were shown to be good substrates for calf intestine alkaline phosphatase (highest activity at alkaline pH) and phosphomonoesterases of partially purified beef brain cytosol (highest activity at physiologic pH). Cationic amphiphilic drugs inhibit the actions of alkaline phosphatase on the dioctanoyl analog, but did not inhibit enzymatic hydrolysis of p-nitrophenyl phosphate. In contrast, the beef brain cytosolic fraction p-nitrophenyl phosphate hydrolysis was mildly inhibited, and the phosphatidic acid analog hydrolysis was increased slightly. Tetramisole inhibited all enzyme activities with p-nitrophenyl phosphate, but was inhibitory only to the alkaline-phosphatase activity with the phosphatidic acid analog.