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We show that for any positive integer n, the multiplicative semigroup Zn has the property that the set of bi-ideals and the set of quasi-ideals coincide if and only if either n = 4 or n is square-free.AMS Subject Classification (1991): 20M10  相似文献   
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The surface modification of cellulose fabric with chitosan was achieved through an oxidation of the fabric with KIO4 followed by reductive ammination with chitosan. The chitosan content in the fabric determined by Kjeldahl nitrogen analysis technique was 1.69%. The scanning electron micrograph revealed submicron particles of chitosan attached on the fabric surface. Dyeing of the modified fabrics with mono-chloro-triazine and vinyl sulfone anionic reactive dyes, showed vastly improved exhaustion and color yield (K/S) indicating that this method of surface modification is effective for changing surface activity of the fabric. The enhancement of the dye uptake brought about an improved dyeing process in which the dye and salt used could be reduced by half and 14%, respectively. A Significant drop in burst strength upon the oxidation but no discernable adverse color fastness property was observed for the chitosan-modified fabric.  相似文献   
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Let V and W be vector spaces over a division ring D and LD (V, W) the set of all linear transformations from V into W. For LD(W, V), let (LD (V, W), ) denote the semigroup LD (V, W) with the operation * defined by * = for all , LD(V, W). By a unit-regular semigroup we mean a semigroup S with identity having the property that for each a S, a = aua for some unit u S. The main purpose of this paper is to prove the following statements. The semigroup (LD(V, W), ) is regular if and only if V = {0}, W = {0} or is an isomorphism from W onto V. The semigroup (LD (V, W), ) is unit-regular if and only if (i) V = {0}, (ii) W = {0} or (iii) is an isomorphism from W onto V and dimD V .  相似文献   
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Particulate matter (PM) air pollution has a significant impact on human morbidity and mortality; however, the mechanisms of PM-induced toxicity are poorly defined. A leading hypothesis states that airborne PM induces harm by generating reactive oxygen species in and around human tissues, leading to oxidative stress. We report here a system employing a microfluidic electrochemical sensor coupled directly to a particle-into-liquid sampler (PILS) system to measure aerosol oxidative activity in an on-line format. The oxidative activity measurement is based on the dithiothreitol (DTT) assay, where, after being oxidized by PM, the remaining reduced DTT is analyzed by the microfluidic sensor. The sensor consists of an array of working, reference, and auxiliary electrodes fabricated in a poly(dimethylsiloxane)-based microfluidic device. Cobalt(II) phthalocyanine-modified carbon paste was used as the working electrode material, allowing selective detection of reduced DTT. The electrochemical sensor was validated off-line against the traditional DTT assay using filter samples taken from urban environments and biomass burning events. After off-line characterization, the sensor was coupled to a PILS to enable on-line sampling/analysis of aerosol oxidative activity. Urban dust and industrial incinerator ash samples were aerosolized in an aerosol chamber and analyzed for their oxidative activity. The on-line sensor reported DTT consumption rates (oxidative activity) in good correlation with aerosol concentration (R(2) from 0.86 to 0.97) with a time resolution of approximately 3 min.  相似文献   
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Recently, the development of electrochemical biosensors as part of microfluidic devices has garnered a great deal of attention because of the small instrument size and portability afforded by the integration of electrochemistry in microfluidic systems. Electrode fabrication, however, has proven to be a major obstacle in the field. Here, an alternative method to create integrated, low cost, robust, patternable carbon paste electrodes (CPEs) for microfluidic devices is presented. The new CPEs are composed of graphite powder and a binder consisting of a mixture of poly(dimethylsiloxane) (PDMS) and mineral oil. The electrodes are made by filling channels molded in previously cross-linked PDMS using a method analogous to screen printing. The optimal binder composition was investigated to obtain electrodes that were physically robust and performed well electrochemically. After studying the basic electrochemistry, the PDMS-oil CPEs were modified with multi-walled carbon nanotubes (MWCNT) and cobalt phthalocyanine (CoPC) for the detection of catecholamines and thiols, respectively, to demonstrate the ease of electrode chemical modification. Significant improvement of analyte signal detection was observed from both types of modified CPEs. A nearly 2-fold improvement in the electrochemical signal for 100 μM dithiothreitol (DTT) was observed when using a CoPC modified electrode (4.0 ± 0.2 nA (n = 3) versus 2.5 ± 0.2 nA (n = 3)). The improvement in signal was even more pronounced when looking at catecholamines, namely dopamine, using MWCNT modified CPEs. In this case, an order of magnitude improvement in limit of detection was observed for dopamine when using the MWCNT modified CPEs (50 nM versus 500 nM). CoPC modified CPEs were successfully used to detect thiols in red blood cell lysate while MWCNT modified CPEs were used to monitor temporal changes in catecholamine release from PC12 cells following stimulation with potassium.  相似文献   
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Given a semilattice Y of inverse semigroups S, there corresponds a semilattice Y of groups G in a natural way. This correspondence is used to study semilattices of proper inverse semigroups. In paticular, it is shown that if S is a semilattice of proper inverse semigroups, then there exists a minimum semilattice congruence such that each -class is proper and there exists a maximum semilattice congruence such that each -class is proper.  相似文献   
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