Comparison of activities in selective catalytic reduction of NOx by C3H8 over Co/MFI, Fe/MFI, and H/MFI zeolite catalysts

The Co/MFI(SiO₂/Al₂O₃ = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N₂ at 250 °C for the selective catalytic reduction (SCR) of NO_x. These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)---O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl₂ exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some Fe---O species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs.     

The molecular interaction of Fas and FAP-1. A tripeptide blocker of human Fas interaction with FAP-1 promotes Fas-induced apoptosis

Fas (APO-1/CD95), which is a member of the tumor necrosis factor receptor superfamily, is a cell surface receptor that induces apoptosis. A protein tyrosine phosphatase, Fas-associated phosphatase-1 (FAP-1), that was previously identified as a Fas binding protein interacts with the C-terminal 15 amino acids of the regulatory domain of the Fas receptor. To identify the minimal region of the Fas C-terminal necessary for binding to FAP-1, we employed an in vitro inhibition assay of Fas/FAP-1 binding using a series of synthetic peptides as well as a screen of random peptide libraries by the yeast two-hybrid system. The results showed that the C-terminal three amino acids (SLV) of human Fas were necessary and sufficient for its interaction with the third PDZ (GLGF) domain of FAP-1. Furthermore, the direct cytoplasmic microinjection of this tripeptide (Ac-SLV) resulted in the induction of Fas-mediated apoptosis in a colon cancer cell line that expresses both Fas and FAP-1. Since t(S/T)X(V/L/I) motifs in the C termini of several other receptors have been shown to interact with PDZ domain in signal transducing molecules, this may represent a general motif for protein-protein interactions with important biological functions.     

Nonlinear influence on PM-AM conversion measurement of groupvelocity dispersion in optical fibres

The authors propose a method for measuring the group velocity dispersion, including the polarity, of optical fibre by using a single wavelength light source. The method is based on the interplay between phase modulation-amplitude modulation (PM-AM) conversion and self-phase modulation (SPM)     

Mutations can cause large changes in the conformation of a denatured protein

Deletion of 13 amino acids from the carboxyl terminus of staphylococcal nuclease (WTSNase delta) results in a denatured, partially unfolded molecule that lacks significant persistent secondary structure but is relatively compact and monomeric under physiological conditions [Shortle & Meeker (1989) Biochemistry 28, 936-944; Flanagan et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 748-752]. Because of these and other properties of the SNase delta polypeptide, it is a useful model system for investigating the conformation of the denatured state of a protein without using extreme temperature or solvent conditions. Moreover, since the modification is a carboxyl-terminal deletion, SNase delta may also resemble a transient state of the polypeptide chain as it emerges from a ribosome prior to its folding. In the present study, we have examined the sizes and conformations of mutated forms of SNase delta, using small-angle X-ray scattering and circular dichroism spectroscopy. Seven mutated forms were studied: four with single substitutions, two with double substitutions, and one triple substitution. When present in the full-length SNase, each of these mutated forms exhibited unusual behavior upon solvent or thermal denaturation. In the case of the truncated form (SNase delta), the small-angle scattering curves of the mutated forms fall into two classes: one resembling the scattering curve of compact native nuclease and the other having features consistent with those expected for an expanded coil-like polymer. In contrast, the scattering curve of WT SNase delta exhibits features intermediate between those observed for globular proteins and random polymers. The amino acid substitutions that gave rise to compact, native-like versions of SNase delta were all of the m--type (m-substitutions are predicted to decrease the size of the denatured state). Those which gave rise to versions of SNase delta that were more extended and coil-like than WT SNase delta were of the m+ type (m+ substitutions are predicted to increase the size of the denatured state). Estimates of the residual secondary structure present in WT SNase delta, as well as both the m+ and m-substituted versions of SNase delta, as determined by CD, suggest that the formation of secondary structure and compaction of the polypeptide chain occur concurrently. Our results show that single amino acid substitutions can radically alter the conformational distribution of a partially condensed polypeptide chain.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fully methylated oriC with negative superhelicity forms an oriC-membrane complex before initiation of chromosome replication

In an in vitro assay, the oriC DNA has been shown to bind to the outer membrane fraction only when it is hemimethylated (G.B. Ogden et al., Cell, 54, 127-135,1988). In this report, however, we demonstrated that a significant amount of the oriC DNA was recovered from the cells just before initiation with the oriC DNA being fully methylated. Formation of this preinitiation oriC-membrane complex and following initiation of chromosome replication were strongly inhibited by novobiocin, a DNA gyrase B subunit inhibitor, which reduced the superhelicity of the reporter plasmid in the cells. On the other hand, both reactions proceeded in the presence of nalidixic acid, a DNA gyrase A subunit inhibitor, which did not have the effect of reducing the superhelicity. These results suggest that the negative superhelicity of the DNA is required for preinitiation oriC-membrane complex formation and following initiation event of replication.     

Mean molal activity coefficients of aqueous scandium chloride, nitrate, bromide and perchlorate solutions at 25.0°

The mean molal activity coefficients of aqueous scandium chloride, nitrate, bromide and perchlorate solutions were determined at 25.0° for dilute to saturated concentrations, together with the activities of water. In the dilute solutions of scandium halides, the activity coefficients were obtained from electromotive force measurements on galvanic cells, and the osmotic coefficients of all four solutions above 0.1 mol kg⁻¹ were determined from the isopiestic measurements. Least-squares equations were fitted to these coefficients, which were then used to calculate the mean molal activity coefficients and water activities. The relationships between these results and the corresponding activity data for other rare earth salts, and to the cation hydration and ionic interactions, are discussed. The results on scandium perchlorate solutions suggested that the inner-sphere hydration number of tervalent scandium ion may be seven.     

Neutronic and thermodynamic feasibility of UF6-NpF6 fueled transmutation reactor

Transmutation of neptunium, which is contained in radioactive wastes discharged from nuclear reactors, was investigated as a substitutional method for geologic disposal. We proposed a transmutation reactor fueled with a mixture of gaseous ²³³UF₆ and ²³⁷NpF₆. Neutronic and thermodynamic analysis of the reactor revealed the feasibility of the concept. The reactor has two principal advantages: (1) use of the fuel gas enables on-line reprocessing, (2) ²³⁷Np can be transmuted by a high neutron flux. Our calculation indicated that the transmutation rate of ²³⁷Np was 335 g/year/MW_th, which is much larger than the annual yield of ²³²Np in PWR (6.19 g/year/MW_th).     

Performance analysis of disk allocation method usingerror-correcting codes

The problem of distributing a Cartesian product file on multiple disks to maximize the parallelism for partial match queries is addressed. C. Faloutsos et al. (1989) have proposed an allocation method for Cartesian product files on multiple disks by using linear error-correcting codes. The performance of the allocation method is analyzed. Some conditions under which the allocation method is strictly optimal for queries with a given number of unspecified attributes are presented. A necessary and sufficient condition for a linear code to give a strictly optimal allocation method is discussed. Formulas for the average response time on queries with w unspecified attributes, denoted T_w, in terms of the weight distribution of the code or its dual code, and formulas for the average response time Ton all queries, are given. Several examples whose average response times T_w or T are close to theoretical lower bounds are presented     

State feedback control of current-type PWM AC-to-DC converters

A control method for current-type PWM AC-to-DC converters that realizes a sinusoidal AC input current and unity power factor is discussed in detail. In such converters, an LC filter placed on the AC side may cause a resonant problem, especially in the transient condition. To overcome this problem, state feedback control is introduced, and a control strategy suitable for DC-output current control as well as AC-side current control is proposed. Circuit parameters and feedback coefficients in the AC-side current control system are optimized on the basis of an analysis in which the system is treated as a sampled-data system. A method of investigating parameters in the DC-side current control system is shown. To confirm the effectiveness of the control strategy and the validity of the analytical results, an experimental investigation of the basic characteristics of the system is made. As an example, this system is applied to controlling the current waveform in the reactor. The experimental results for this application are also included     

A novel technique for a DC brushless motor without position sensors

A dc brushless motor is a kind of synchronous motor driven by an inverter and requires sensors to detect the rotor position. As one of the methods, the induced voltages of a brushless motor have been utilized in practice. However, there are some problems in this method, e.g., the motor can obtain insufficient torque due to the low induced voltages in a low-speed range. This paper proposes a new method which controls the inverter angular frequency ω₁ by using inherent characteristics wherein the torque current i_r is almost proportional to the internal phase angle φ where the primary flux of a synchronous motor is controlled to be constant. If the parameters of a motor are given exactly, the speed regulation is quite small and the transient characteristics with high response and high starting torque are obtained. Furthermore, it is possible to operate a synchronous motor in the field-weakening range. Here, the principle of the control method and the performance characteristics of a dc brushless motor having no position sensors are discussed. The simulation and the experimental results of the tested machine show that the proposed method is very useful for practical applications.