Internal Filter Research Articles

Stern–Volmer quenching kinetics in photoreaction systems with strong internal filtering: Type II photoreaction of 2‐benzoylcyclohexanone

AbstractThe Stern–Volmer quenching equation for a photochemical reaction in the presence of internal filtering was obtained by applying the steady‐state approximation to the system. The equation was used for the kinetic analysis of the Type II photoreaction of 2‐benzoylcyclohexanone yielding 1‐phenylhept‐6‐ene‐1,3‐dione, the enol form of which acts as an effective internal filter. The kqτ value for quenching of the photoreaction by 2,5‐dimethylhexa‐2,4‐diene was determined to be 9·1 ± 0·5 l mol−1.

Relative liquid removal in filtration and expression

A strong relationship exists among the nature of particles in a suspension, properties of the particulate structures forming cakes and sediments, and the best operating procedure for reducing liquid content. Matrices of particles can be crudely classified into (1), super-compactible flocs, (2), highly compressible cakes formed from substances having bound water (clays), (3), moderately compressible, and (4), nearly incompressible materials. Super flocs with little internal strength filter easily by gravity or low pressure and do not respond to increased pump pressure. They require a squeezing process. Highly compressible materials such as attapulgite clay or colloidal silica filter with great difficulty, and high pressure pumps are not effective. They also require expression for substantial reduction of porosity. Moderately compressible cakes exhibit more favourable behaviour with increasing pressure. Incompressible cakes cannot be deliquored by expression. However, if the particles are large enough, suction, blowing, or centrifugal filtration are generally successful for liquor removal. The applied pressure must be greater than the capillary suction. A simple experimental technique for evaluating cake behaviour is provided.

A digital signal processor for an ANSI standard ISDN transceiver

The digital signal processing chip of a two-chip ISDN (integrated services digital network) basic access transceiver based on the ANSI standard 2B1Q code is described. Nonlinear echo cancellation is used to improve the loop coverage. The chip features a multiprocessor architecture, where each processor is optimized for the algorithm used. Full observability of internal signals and adaptive filter coefficients is supported. The device is fabricated in a 1.25- mu m double-level-metal CMOS process with an active area of 47 mm/sup 2/. >

Efficient computation of multichannel Wiener filters with linear phase

A family of fast-lattice and transversal algorithms for multichannel linear-phase (LP) Wiener filters is developed. Due to the strong symmetry properties imposed by the phase constraints, the proposed computational process involve only one internal filter that propagates according to a Durbin-like recursion, in contrast to unconstrained multichannel Wiener filtering (absence of phase constraints) where both the forward and backward predictors are carried, coupled in a pair of Levinson-like recursions. Normalized lattice realizations are derived using a suitable power-sum normalization and parameterized by internal reflection coefficients with singular values inside the unit circle.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Determination of pyridine nucleotide fluorescence from the perfused heart using an internal standard.

Mitochondrial reduced nicotinamide adenine dinucleotide (NADH) is a key intermediate in energy metabolism in the heart, which can be qualitatively monitored using nondestructive surface fluorescence techniques. However, this optical technique is subject to artifacts from alterations in tissue absorbance, motion of the heart, and variations in excitation intensity. In this study rapid-scan fluorescence emission spectroscopy was used in conjunction with an internal fluorescence standard to compensate for these optical artifacts. The fluorescence spectra obtained from heart had a maximum at 460 nm and a shoulder at 415 nm. Dilution of heart homogenates resulted in a fluorescent spectrum characteristic of suspensions of mitochondria, indicating that absorption of fluorescence by tissue components produces an inner filter effect. This internal filter was characterized, and isobestic points with regard to O2 were found at 425 and 450 nm. Alterations in the inner filter effect due to changes in tissue oxygenation were eliminated by monitoring the NADH at 425 nm. Motion artifacts and excitation source fluctuations were corrected by loading heart cells with an internal fluorescent standard, 5(6)-carboxy-2',7'-dichlorofluorescein (ClCF). Motion of the heart and changes in excitation intensity altered the fluorescence detected from both NADH and ClCF. The use of the NADH-to-ClCF ratio detected at isobestic wavelengths (425 nm NADH and 520 nm ClCF) gives a relative measure of NADH fluorescence, which adequately compensates for both internal absorbance and motion artifacts.

Effect of masker bandwidth on the detection of signals at unexpected frequencies

In wideband noise, listeners tested with the probe-signal method [G. Z. Greenberg and W. D. Larkin, J. Acoust. Soc. Am. 44, 1513–1523 (1968)] detect a signal at an expected frequency (primary) while missing signals at a far, unexpected frequency (probe). The present experiments test the hypothesis that the internal filter is narrowest at the primary frequency, thereby admitting less external noise there. According to this hypothesis, the probe should be as detectable as the primary when the external masker is narrower than the internal filter. Against wideband noise, subjects detected a 1-kHz primary on 90% of the trials and a 2-kHz probe on 60% of the trials. Against two simultaneous subcritical noises—one at 1 kHz, the other at 2 kHz—results were similar. With the noise at 2 kHz narrowed to 50 Hz, 6 of 12 subjects detected the probe reliably, possibly because the strong pitch of the masker drew attention to the 2-kHz probe. Overall, these results suggest that attention does not affect the width of the internal filter. [Work supported by NIH.]

Microcomputer-controlled two size-fractionating aerosol sampler for outdoor environments

A microcomputer-controlled aerosol sampler has been constructed to give an optimized sampling system for measurements in outdoor environments compatible with particle-induced X-ray emission (PIXE) analysis. Aerodynamic, mechanic, and electronic principles of this sampler are discussed. The sampler has a capacity of 70 samples at the maximum flow rate of 5 L/min. The larger particles are collected on an impactor stage, and the smaller particles are deposited on a filter after the impaction stage. It is easy to vary the cutoff diameter from 1 to 5 ..mu..m and the deposition area on the filter to suit the demands of the specific sample situation or to obtain the best possible detection limits. Tests carried out to investigate internal losses, impactor characteristics, and filter efficiency are presented. At the maximum flow rate the total losses, including wall losses, bounce off, and filter leakage, are of the 5-15% range for particle sizes between 0.05 and 10 ..mu..m.

Type II photoreactions of α-alkyl β-oxoesters. Neighboring group effect on 1,4-biradical reactions and effective internal filter effect by the type II photoproduct

The α-alkyl β-oxoesters 1 undergo type II photoreactions. The process of back hydrogen transfer in the 1,4-biradical intermediate to revert to the starting ester is suppressed because of the intramolecular hydrogen bonding between the hydroxyl and carboalkoxyl groups in the biradical intermediate. The hydrogen bonding determines the stereochemistry of 1,4-biradical cyclization. The cyclobutanols having the hydroxyl group cis to the carboalkoxyl group are formed exclusively from the α-alkyl β-oxoesters 1 . The enol form of the type II elimination product, the benzoylacetate 2 , acts as an effective internal filter for the photoreaction of the α-alkyl β-oxoester 1 .

Filter Criteria for Geotextiles: Relevance and Use

Thm general requirements for filters, both granular and geotextile, in one-directional flow applications and the relevant geotextile properties affecting good filtration performance are presented. The relevance of existing one-directional geotextile filter criteria is also examined. An application involving the specification and performance evaluation of a geotextile for an internal filter in an earth dam, constructed on flyash, where large hydraulic heads were anticipated at the flyash-geotextile interface (up to 10.8 m) validated the use of existing geotextile filter criteria.

Comparison of frequency selectivity for the monaural and binaural hearing systems: Evidence from a probe-frequency procedure

Frequency selectivity was measured for one monaural system condition (NOSO) and two binaural system conditions (NOSπ and NOSM) using the probe-frequency method originated by Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. Subjects were first trained to detect a 500-Hz tone in noise for each condition of the experiment. Following training, the usual detection paradigm was altered such that on 25% of the trials a second signal of a different frequency was substituted for the 500-Hz signal. Performance at each of these secondary or probe-frequencies was transformed into equivalent decibels of attenuation by means of psychometric functions obtained at 500 Hz. A correction was then applied to these data which compensated for the relationship between frequency and the size of the MLD. The transformed and corrected data were interpreted as describing attenuation characteristics of an internal auditory filter. No systematic difference was found between attenuation characteristics for the two binaural system conditions. However, the attenuation characteristics for the binaural system conditions were approximately twice as wide as those for the NOSO condition.

Specific binding of fluorescein labelled serum retinol-binding protein to its cell surface receptor in isolated, purified bovine pigment epithelial cells

Purified bovine pigment epithelial cells were labelled specifically with fluorescein tagged serum retinol-binding protein. This labelling was specific for serum retinol-binding protein and for pigment epithelial cells. The fluorescent label was confined to the choroidal surface of the cell. The hemicellular labelling pattern was used for a vectorial orientation of isolated cells, using the melanin pigment as an internal filter for fluorescence. Fluorescent labelled hexokinase, an unrelated protein, did not show specific labelling of pigment epithelial cells. Prealbumin, which circulates in plasma as a tight complex with retinol-binding protein, did not bind to pigment epithelial cells. Retinol-binding protein can act as a bridge between the pigment epithelial cell surface receptor and fluorescein tagged prealbumin. This suggests that the topological sites of the retinol-binding protein molecule for binding to the cell surface receptor and to prealbumin are different.

Ceric/thallous dosimetry at less than 1000 rad

The ceric/thallous system has been investigated as a low level dosimeter using fluorimetry for the radiation-produced cerous ion. Excellent linearity between the increase in the cerous ion concentration and the dose was obtained using an aerated solution of 13 μM Ce(IV), 6μM Ce(III), 20 μM Tl(I) in 0.4 M H 2SO 4. G(Ce 3+) was found to be 7.56 ± 0.08. The internal filter effect caused by the ceric ions is not a problem provided that the initial concentration is less than 15 μM since the same G(Ce 3+) value was obtained regardless of whether the results were corrected for the internal filter or not. The most serious disadvantages of the system appear to be light sensitivity and thermal reduction of ceric ions. The thermal reduction is most rapid immediately after solution preparation and requires a delay of about one month before stability is achieved.

The range of spectral integration.

The results of two complementary detection tasks using digitally synthesized noise are reported. In one experiment the bandwidth of the synthetic noise was varied to reveal the region most effective in masking a 1-kHz signal. The bandwidth of the internal filter ("critical band") so measured was about 80 Hz. In another experiment, a wideband noise was used as the masker for a synthetic signal whose bandwidth another experiment, a wideband noise was used as the masker for a synthetic signal whose bandwidth was varied to determine the maximum effective width of the internal filter. Although some earlier experiments suggest maximum effective widths as small as 180-200 Hz (around 1 kHz), the data reported here indicate the range of spectral integration extends from the critical band to a maximum width that may exceed 3 kHz. In addition, the good agreement between the two experiments suggests a new method for estimating critical bandwidths based on the determination of two thresholds: that of a tonal signal in a wideband masker and that of a supracritical-width noise signal in a wider-bandwidth masker.

Photocyclization of β-oxo-amides. Possible electron transfer from amide nitrogen to excited ketone carbonyl

Benzoylacetamide (1a) undergoes unquenchable photocyclization to give pyrrolidin-2-one (2a) in benzene. Upon irradiation p-phenylbenzoylacetamide (1d) and 2-naphthoylacetamide (1e) also undergo cyclization to give the pyrrolidin-2-ones (2d) and (2e), respectively. The quenchable portion of the photoreaction of (1a) is greater in methanol than in benzene. Benzoylacetamides having a 2-methyl substituent exhibit similar behaviour although the quenchable portion of the reaction increases with an increase in the number of the 2-methyl substituents. The photoreaction of 2,2-dimethylbenzoylacetamide (1c) is completely quenched by piperylene in methanol. Quantum yields also increase with introduction of a substituent into β-oxo-amides except in the photocyclization of 2-naphthoylacetamides. Irradiation of N-benzyl-N-methyl-β-oxo-amides (1g–i) affords, predominantly, 1-benzylpyrrolidin-2-ones, which are produced via methyl hydrogen abstraction; 2-methyl-β-oxo-amide (1j) however gives 1-methylpyrrolidin -2-one (2j) exclusively, which is formed via benzylic hydrogen abstraction. It is concluded that β-oxo-amides which have no substituents on the 2-position undergo photocyclization mainly through electron transfer from amide nitrogen to singlet-excited ketone carbonyl followed by δ-proton transfer, while β-oxo-amides which carry two methyl substituents on the 2-position undergo the cyclization via normal δ-hydrogen abstraction from the n,π* triplet state. The enol form of β-oxo-amides acts as internal filter in the photoreactions.

Critical Bandwidth in Menière's Disease

The critical bandwidth in loudness summation was estimated in 20 patients with typical Menière's disease using noise bands centered around 1 kHz. A reduction of the normal loudness difference between broad-band noise and narrow-band noise was present at all except the highest levels. Judged individually, 7 of the 20 patients appeared to have a widened critical band, but in the pooled data the size of the critical band was normal. This was the case in patients with a hearing loss less than 50 dB HL as well as in patients with a hearing loss greater than or equal to 50 dB HL. Expressed in terms of the critical band mechanism as an internal filter system, the single filter appears to have normal bandwidth but the interaction between adjacent filters is defective. The anatomical localisation of this interaction is discussed.

Man as a mammal: Psychoacoustics

In trying to describe the auditory capabilities of vertebrates, investigators often use measures of critical bands, temporal integration or localization. The results obtained from nonhuman animals are quite often compared to classical data obtained from man. In recent years both psychoacousticians and auditory physiologists have begun to modify the classical theories of frequency selectivity, temporal acuity, and localization. The concept of an internal filter to describe frequency selectivity has given way to more complex functions that indicate frequency regions of excitation and inhibition. Measures of the time constant of temporal integration have varied from a few to hundreds of milliseconds indicating complex temporal processing. The ability of man to accurately lateralize high‐frequency sounds that contain low repetition frequencies has challenged the original duplex theory of localization. The research in these three areas will be reviewed in the context of comparative animal psychophysics.

Contribution a l'Étude de la Biologie de la Larve de Stratiomyia Longicornis [Diptera, Stratiomyiidae]: Prise de Nourriture et Respiration

SummaryThe bucco-pharyngeal apparatus is composed of four successive formations: an external filter, an external triturating apparatus, an internal filter and an internal triturating apparatus preceding the œsophagus. Greater importance is attributed to the external apparatuses; the internal triturating apparatus is compared to the microstructures of the molas of Crustacea.The structure of the stigmas, whether functional or not, and of the trachean system is defined.

Frequency selectivity in the parakeet: The relation between critical band and psychophysical tuning curves

The critical band may be viewed as an indication of the bandwidth of the internal auditory filter. The bandwidth of a filter, as a measure of its frequency selectivity is not easily compared with the bandwidths of other filters. One useful measure of frequency selectivity, however, can be found by dividing the bandwidth of a filter at some arbitrary point below the peak, into the center frequency of the filter. This so called “Q” measure is valuable because it represents a ratio and thus can be compared among filters of different center frequencies. We have assumed that indirect measures of the critical band (the critical ratio) represent the bandwidth of the internal filter at a consistent point below the peak. We have thus calculated a Qcritical ratio for all the available data points in the parakeet. Psychophysical tuning curves (PTC) have been empirically obtained for eight different probe frequencies in the parakeet. A Q10 dB was calculated for each of these tuning curves and compared with the data describing Qcritical ratio, at ten different frequencies. The plot over frequency of Qcritical ratio and Q10 dB of the PTC's, although differing in absolute values, were nearly identical in shape. Frequency selectivity is poor in the low frequencies, raises sharply between 2.5 and 4.0 kHz, and then becomes poor again at higher frequencies. The results will be discussed with regard to the relation between the critical band and psychophysical tuning curves and frequency selectivity in the parakeet. [Work supported by NSF.]

Simultaneous intraparticle forced convection, diffusion and reaction in a porous catalyst—II: Selectivity of sequential reactions

The selectivity of a sequence of isothermal irreversible heterogeneous reactions ▪ within a catalytic pellet is investigated under conditions where intraparticle forced convection is a non-negligible transport mechanism. The nature of the effect of the internal filter flow depends mostly on the value of the Thiele modulus, φ 2, of the desired (middle) species. The asymptotic values of the selectivity, as φ 2 → 0 and φ 2 → ∞, are unaltered, independent of the strength of the internal flow. The intermediate region is divided into two parts. In the subregion with lower values of φ 2 the selectivity is enhanced. In the other subregion, with higher values of φ 2, the selectivity is significantly retarded to values which can be markedly below the lower asymptote. These trends are common to both poor and good selective catalysts.

Spectral considerations in the laser isotope separation of Uranium Hexafluoride

Key spectral features important in the laser isotope separation of Uranium Hexafluoride are reviewed. Specifically the (v 3+v 4+v 6) band lying in the frequency range of the CO2 laser, the 3v 3 band which is covered by the CO laser, and the fundamentalv 3 band of UF6 are considered. Computer-calculated spectra show that the ternary combination bands (v 3+v 4+v 6) and 3v 3 are completely dominated by the solid Q-branches of some 300 to 1000 hot bands, but that the fundamentalv 3 band has structured P-and R-branches with peaks and holes, provided the pressure is below a few torr. Laser isotope separation can be achieved either on the isotope-shifted slopes of the Q-branches envelopes (“Q-slope method”) or on the coincidence of a peak and a hole in the P-or R-branches regions (“peak-hole method”). Room temperature experiments were carried out in 1972/1973, which used a CO2 laser with an internal U238F6 filter tube that forced lasing on what is believed to have been the P-16 line falling on the right-hand Q-slope of the (v 3+v 4+v 6) band of UF6. With a chemical reaction for final isotope separation, the measurements yielded a U-235 enrichment factor of about 1.1, in agreement with the maximum possible value of 1.5 for Q-slope operation and the fact that a high cut was used.