An adaptive threshold filter for ultrasound signal rejection

The threshold filter is a frequently used technique in ultrasound B-scan to reject the small echoes contributed from backscattering that blur the tissue interface and reduce the image contrast. Note that using the threshold based on one value would simultaneously destroy local waveform features of the reflection echoes with amplitudes larger than threshold value. To resolve this problem, we developed an adaptive threshold filter based on the noise-assisted empirical mode decomposition (EMD). Computer simulations at 7.5 MHz using a single-element transducer with a bandwidth of 60% and a pulselength of 0.5 μs were carried out to explore the feasibility of the algorithm. Image measurements on the carotid artery using a 7.5 MHz, 128 elements, 1D linear array transducer with the same characteristics as those in simulations were used to verify the performance of the algorithm in practice. Compared to the result from the conventional threshold technique, the adaptive threshold filter is able to successfully suppress the smaller backscattering signals without changing the local waveform features of the preserved significant echoes due to refection.     

Three-dimensional ultrastructure of the ring stage of Plasmodium falciparum: evidence for export pathways.

The three-dimensional structure of the Plasmodium falciparum ring stage has been explored by reconstruction from serial sections and stereoscopic examination of tilted sections. The ring-like light microscopic appearance is related to the shape and contents of the biconcave discoidal parasite at this stage, its thick perimeter containing most of the ribosomes and its thin center containing smooth membrane organelles. The shapes of rings vary between flat and curved cuplike forms. The rough endoplasmic reticulum is a branched network continuous with the nuclear envelope. Evidence for a simple Golgi complex is seen in the presence on the outer nuclear envelope of a locus of coated vesicle budding associated with a single membranous cisterna or cluster of smooth vesicles. In middle and late stage rings this complex migrates along an extension of the nuclear envelope continuous with the rough endoplasmic reticulum. Evidence is also presented for a mechanism of exporting membrane from the parasite into the parasitophorous vacuole membrane and beyond into the red blood cell, by means of double-membraned vesicle-based exocytosis.     

Zur Unterscheidung von Iridium und Rhodium

Ohne Zusammenfassung     

Methylene substitution reactions in a quadrupole ion trap selectivity of ethylene,ethylene oxide,and dimethyl ether reactive ions

To elucidate the selectivity of methylene substitution reactions of monosubstituted and disubstituted oxyaromatic compounds in a low pressure quadrupole ion trap environment, the relative abundances of covalently bound and loosely bound adducts formed by ion/molecule reactions with ethylene (ET), ethylene oxide (ETOX), and dimethyl ether (DME) were compared. Adduct ions of all three reagent gases were formed in both a conventional ion source and a quadrupole ion trap and characterized by collisionally activated dissociation. For DME and ET, the covalently bound adducts formed at (M + 45)⁺ and (M + 41)⁺, respectively, are direct precursors to the methylene substitution product ions at (M + 13)⁺. ETOX and ET do not demonstrate the same functional group selectivity for methylene substitution as previously observed for DME. This is attributed to differences in reaction exothermicities and competing reactions.     

Highly conductive and thermally stable self-doping propylthiosulfonated polyanilines

A new type of highly conductive self-doping polyaniline, MPS-Pan, containing a sulfonic acid moiety covalently bonded to the polymer backbone through an electron-donating propylthio linkage has been successfully prepared via a novel concurrent reduction and substitution route. At a similar self-doping level, the resultant MPS-Pans displayed much higher conductivity than the corresponding sulfonated-polyaniline (S-Pan). Furthermore, for fully doped samples, contrary to the trend of decreasing conductivity with the sulfonation degree in S-Pan, the conductivity of MPS-Pan was found to increase with its substitution degree. These results agreed with the expectation that electron-deficient charge carriers (e.g. semiquinone radical cations) on acid-doped polyaniline chains will be better stabilized by the electron-donating alkylthio-substituent. Surprisingly, TG and XPS studies showed that MPS-Pan was thermally much more stable than S-Pan, with S-Pan started to lose its sulfonic acid dopant at 185 ℃, while MPS-Pan remained intact up to ca. 260 ℃.     

Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M₁ + Cat + M₂)⁺, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M₁ + Cat)⁺ and (M₂ + Cat)⁺ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li⁺, Na⁺, and K⁺ than the larger ions such as Cs⁺ and Rb⁺. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.