Comparison of photophysical and colloidal properties of biocompatible semiconductor nanocrystals using fluorescence correlation spectroscopy

A number of different surface chemistries have been developed in recent years to render semiconductor nanocrystals (NCs) stable in water and biocompatible. However, most of these surface modifications affect NCs' photophysical properties, calling for a method to simultaneously monitor colloidal and fluorescence properties. Fluorescence correlation spectroscopy (FCS) combined with ensemble spectroscopic methods and Monte Carlo simulations were used to interpret and derive photophysical as well as colloidal properties of four different NC surface treatments. Using a novel FCS scheme with alternating laser excitation at two different intensities, we first ruled out influences from optical gradient forces (optical trapping). We then compared concentration of emitting particles, brightness per particle, saturation intensity, blinking (intermittency), hydrodynamic radius, and propensity for aggregation of the different bioconjugated NCs. This approach was successfully applied during the development and optimization of peptide-coated NCs.     

Micromechanical fracture analysis of amylose

Amylose films were prepared with two distinctly different microstructures, and these specimens were subsequently tensile-tested at different levels of moisture content. Measurement of the strain energy release rate, G_l, was approached from three separate methods. Two of these methods, the J integral and stress intensity analyses, are based on bulk tensile properties. The third method involves direct calculation of the work expended in producing the microplastic zone at the crack tip. Birefringence measurements were used in mapping the magnitude and shape of the plastic zones. Although the semicrystalline material would not lend itself to the bulk tensile analyses, G_l values were obtained via the optical analysis. For disordered amylose, G_l values derived from this optical analysis were found to correlate with those obtained from bulk measurements, and the fracture toughness was found to be comparable to that of other engineering polymers. Surprisingly, moisture content within the range investigated herein has no great effect on the strain energy release rate. This insensitivity is attributed to active interaction between the absorbed water and amylose macromolecules.     

Shiga toxigenic Escherichia coli show strain dependent reductions under dry-fermented sausage production and post-processing conditions

Dry-fermented sausages (DFS) are considered possible risk products regarding Shiga toxigenic Escherichia coli (STEC). We have compared the reduction of 11 E. coli isolates of various serogroups in salami during the sausage production process and during post-process measures including storage, heating and freezing. The 11 E. coli isolates, mainly STEC, included enterohaemorrhagic E. coli (EHEC) outbreak strains linked to DFS along with apathogenic E. coli. During sausage production, there was a statistically significant difference in reduction between the E. coli strains ranging from 1.3 to 2.4 log?? (p<0.001). When sausages were subjected to post-process heat treatment of 43 °C for 24 h, a total reduction of more than 5 log?? was obtained for all E. coli isolates. Freezing and thawing of DFS with subsequent storage for 1 month at 16 or 20 °C generally contributed to large E. coli reductions with the latter conditions giving an average additional 3.9 log?? reduction, with a range from 3.4 to 4.4 log??. The combination of freezing and 1 month of storage gave higher reductions compared with storage for 2 months for all examined temperatures. No systematic differences in survival of E. coli of different serogroups were detected for the different post-process measures. The reductions were also similar to those of apathogenic control isolates. Isolates showing higher survival during the ripening process did not have a lower reduction when exposed to post-process stress like storage, heating and freezing. The ability of the isolates to survive in salami was also compared with their survival at equivalent conditions in a tryptic soy broth (TSB) model. There was a low and not significant correlation (p>0.1) between the reductions of E. coli in salami and in the TSB broth model. Results based on broth models and/or single or surrogate strains must therefore be interpreted with caution. The EHEC reducing post-processing measures tested can easily be implemented in DFS production with marginal influence on the quality of the sausages.     

A Low-Pressure Excimer Light Source for a Spectral Region of 170–310 nm

A low-pressure excimer light source pumped by a longitudinal dc glow discharge operates on the B–X and D–X transitions of Ar, Kr, and Xe chlorides and on the D–A transition of chlorine molecules. The output characteristics of a source with a discharge region 100 mm long and an inner diameter of the discharge tube of 5 mm were optimized on Xe(Kr, Ar)/Cl₂, Ar/Kr/Cl₂, Ar/Xe/Cl₂, and Kr/Xe/Cl₂ mixtures. The light source operated within a spectral range of 170 to 310 nm. The average radiation power and operation efficiency were 1.8–8.2 W and 21%, respectively.     

Dynamical Emergence Theory (DET): A Computational Account of Phenomenal Consciousness

Minds and Machines - Scientific theories of consciousness identify its contents with the spatiotemporal structure of neural population activity. We follow up on this approach by stating and...     

Characteristics of transverse volume discharge in Cf2Cl2 and in Ar/Cf2Cl2 mixture

The conditions of ignition and the characteristics are given for a nanosecond transverse volume discharge in Freon-12 (CF₂C1₂) and in an Ar/CF₂C1₂ mixture. It is shown that, in the ultraviolet and visible ultraviolet spectral region, a plasma based on CF₂C1₂ molecules is a source of radiation of excited carbon atoms and Cl₂ molecules. The volumetric stage of the discharge exists atU _charge ≤ 12 kV and [CF₂C1₂] = 0.1–3 kPa, and the current and voltage oscillograms are similar to the respective characteristics of a transverse discharge with prior-to-prebreakdown electron multiplication in He(Ne)/SF6(F2) mixtures. A plasma of an Ar/CF2C12 mixture is a source of radiation of the λ = 258 nm bands for Cl ₂ ^* , 193 nm for ArF, and 175 nm for ArCl. Such sources may be used in short-wave pulse photometry, microelectronics, and photo- and biochemistry.     

A water-vapor electric-discharge vacuum ultraviolet source

The optical emission from a longitudinal dc glow discharge in water vapors (P=0.05–2.5 kPa) was studied in a wavelength range of λ=130–350 nm. It is shown that the discharge in low-pressure water vapors can be used as a source of the vacuum UV (VUV) radiation in the 140–190 nm wavelength range. As the vapor pressure was increased to 2.5 kPa, the emission intensity decreased by one-two orders of magnitude and the main peaks shifted to λ=286 and 306–315 nm. The bands of optical emission from the products of water decomposition agree in position with the emission band edges of the hydroxyl molecule. The obtained results are important for the development of a simple water-vapor electric-discharge VUV source.     

Conjugates of unsaturated fatty acids with propylene glycol as potentially less-irritant skin penetration enhancers

Fatty acids (FA) are well known as efficient enhancers for transdermal delivery of drugs; however, their frequent dermal toxicity limits their regular use. In order to utilize the fatty acid as a safe enhancer devoid of its irritant effect, we have synthesized and evaluated a series of fatty acids conjugated to propylene glycol (FA-PG). Each one of the conjugates was prepared as a mono- or di- acyl ester derivative. The effects of the synthetic enhancers on the porcine skin permeability were evaluated in a diffusion cell system using lidocaine as the model drug. In addition, in vivo examinations in rabbits were preformed for skin toxicological evaluation. The results indicate that among the FA-PG conjugates, oleic acid (C18:1(n-9))-PG, linoleic acid (C18:2(n-6))-PG and alpha-linolenic acid (C18:3(n-3))-PG, mono- or di-esters, enhance the penetration of lidocaine relatively to the vehicle (without enhancer). The conjugates of oleic acid (C18:1(n-9)) and linoleic acid (C18:2(n-6)) with PG have demonstrated a similar enhancing effect as the corresponding free fatty acids. Interestingly, although the mono- or the di- conjugates of alpha-linolenic acid (C18:3(n-3)) with PG enhanced the lidocaine flux as the other two fatty acid conjugates, they resulted in a reduced permeability as compared to the action of their free acid. In addition, the mono-conjugates of alpha-linolenic acid (C18:3(n-3)) with PG exhibited elevated skin irritation in rabbits (relative to the fatty acid alone) compared to the significantly reduced irritation of oleate-PG and linoeate-PG mono-conjugates. In conclusion, except saturated FA-PG and alpha-linolenic acid (C18:3(n-3)) - PG mono-conjugates, unsaturated fatty acids (e.g., oleic and linoleic acids) after conjugation to PG may be safe and effective enhancers for delivering topical drugs.     

Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion

The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400 °C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO(2)-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 μm, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450 °C was found to increase the yield of nanowire nucleation from the gold catalysts.