Noise in miniature microphones

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.     

Mass spectral determination of skeletal/cardiac actin isoform ratios in cardiac muscle

Skeletal and cardiac muscle contains actin isoforms that vary by two juxtaposed amino acids and two amino acid substitutions (Met299Leu and Ser358Thr). This close sequence homology does not allow cardiac and skeletal actin isoforms to be resolved in traditional SDS-PAGE analysis as the molecular weights (Deltamass = 32 Da) are not significantly different and the pIs are identical (5.2). Although cardiac actin is the predominant form in cardiac muscle, there appears to be a specific skeletal/cardiac actin ratio in a normal heart that may vary in a compromised or diseased heart. In an effort to ascertain the validity of this hypothesis we developed a mass spectrometric technique to measure the ratio of skeletal to cardiac actin. The technique involves purification of muscle actin and subsequent liquid chromatography coupled with electrospray ionization Fourier transform ion cylcotron resonance (LC/FTICR-MS) mass spectrometry. A 7 Tesla FTICR mass spectrometer was utilized to compare skeletal/cardiac actin isoform ratios. Additionally, a new dual electrospray ionization source was employed to determine accurate masses of the alpha-skeletal and alpha-cardiac actins.     

Improving chaos-based pseudo-random generators in finite-precision arithmetic

Nonlinear Dynamics - One of the widely-used ways in chaos-based cryptography to generate pseudo-random sequences is to use the least significant bits or digits of finite-precision numbers defined...     

Exogenous crimes and the assessment of public safety efficiency and effectiveness

Annals of Operations Research - This work discusses the issue on how to include data about property and violent crimes in the production technology for the assessment of police technical...     

From potential to reality: Yeasts derived from ethanol production for animal nutrition

A chemical and radiochemical neutron activation analysis (CNAA/RNAA) method has been developed for the determination of three calcium isotopes (⁴⁸Ca,⁴⁶Ca, and⁴⁴Ca) in a single sample derived from urine. This method was developed in support of clinical research using a dual enriched stable isotope methodology to study bone mineralization in premature infants, juvenile rheumatoid arthritics, and cystic fibrosis. In these studies, one enriched isotope of calcium is administered orally, and one is administered intravenously. By making determinations of three isotopes (two enriched, one unenriched) within the same sample, the perturbation from natural isotopic ratios can be determined and used to calculate true absorption of calcium. In our method,⁴⁸Ca is determined via the⁴⁸Ca(n,γ)⁴⁹Ca reaction and 3084 keV gamma-ray,⁴⁶Ca via the⁴⁶Ca(n,γ)⁴⁷Ca reaction and 1296 keV gamma-ray, and⁴⁴Ca via the⁴⁴Ca(n,γ)⁴⁵Ca reaction and 256 keV (max) beta-particle. A pair of chemical separation steps are employed to separate calcium from urine as calcium oxalate with a yield in the range of 80–90%, and a radiochemical step is employed prior to the measurement of⁴⁵Ca to remove interfering radionuclides.     

Coordination-driven self-assembly of supramolecular cages: heteroatom-containing and complementary trigonal prisms

The self-assembly of three nanoscopic prisms of approximate size 1 x 4 nm is reported. Tetrahedral carbon, silicon, and phosphorus were used as structure-defining elements in these coordination-based cages. A carbon-based assembly completes a pair of nanoscopic complementary 3-D structures. The formation of the structures is supported by multinuclear NMR, ESI FT-ICR mass spectrometry, and elemental analysis data.     

Lithium aminoborohydrides 17. Palladium catalyzed borylation of aryl iodides, bromides, and triflates with diisopropylaminoborane prepared from lithium diisopropylaminoborohydride

The Alcaraz-Vaultier borylation of aryl halides and triflates is reported utilizing diisopropylaminoborane (BH₂N(ⁱPr)₂) prepared from the corresponding lithium aminoborohydride (LAB reagent). BH₂N(ⁱPr)₂, prepared by reacting lithium diisopropylaminoborohydride with trimethylsilyl chloride, provided the most consistent isolated yields from this reaction. Catalytic amounts of palladium dichloride produced the highest yields from aryl iodides, while catalytic tris(dibenzylideneacetone)dipalladium(chloroform) provided the best yields for aryl bromides and triflates. This route to boronic acids is mild enough to tolerate various functionalities and for the first time employs aryl triflates as substrates for the Alcaraz-Vaultier borylation. In addition, it was found that both boronic acid and ester compounds could be isolated from the reaction mixture utilizing simple work-up procedures. Treatment of the reaction intermediate with an acid/base work-up provided the corresponding boronic acid, while treating the same intermediate with a diol, such as neopentyl glycol, afforded the corresponding boronic ester.     

Deconvolution of E/Z tetrahydroisoquinoline amide rotamers and conformers from a marine-derived Streptomyces strain

A collaborative program to discover new specialized metabolites from aquatic environments of Iceland led to the deconvolution of tetrahydroisoquinoline amide E/Z rotamers [(E/Z)-N-acetyl-MY336-a; 1] and conformers produced by a Streptomyces sp. All structures were elucidated by NMR and MS analysis, and interpretation of electronic circular dichroism (ECD) data. ECD and optical rotation (OR) simulations permitted the unequivocal assignment of the absolute configuration of compound 1 and provided an important example of delineating the spectroscopic contributions of equilibrating rotamers and boat/chair conformers of a common natural product scaffold.