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21.
We prove that, in Euclidean space, any nonnegatively curved, compact, smoothly immersed hypersurface lies outside the convex hull of its boundary, provided the boundary satisfies certain required conditions. This gives a convex hull property, dual to the classical one for surfaces with nonpositive curvature. A version of this result in the nonsmooth category is obtained as well. We show that our boundary conditions determine the topology of the surface up to at most two choices. The proof is based on uniform estimates for radii of convexity of these surfaces under a clipping procedure, a noncollapsing convergence theorem, and a gluing procedure. 相似文献
22.
Latifeh Navidpour Leila Karimi Mohsen Amini Mohssen Vosooghi Abbas Shafiee 《Journal of heterocyclic chemistry》2004,41(2):201-204
Arylation of the readily available 3‐alkythio‐5‐aryl‐1,2,4‐triazoles gave 5‐alkylthio‐1,3‐diaryl‐1,2,4‐triazoles in moderate yield. The structures of the latter were confirmed by NOE and 13C‐NMR. 相似文献
23.
This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically. 相似文献
24.
Mohammad Reza Ganjali Morteza Rezapour Mohammad Reza Pourjavid Masoud Salavati-Niasari 《Analytical sciences》2003,19(8):1127-1131
A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples. 相似文献
25.
26.
Spin-flip (paramagnetic) scattering and neutron depolarization studies were performed on Ce2Fe17 in its paramagnetic phase on the Dhruva neutron polarization analysis spectrometer. The absence of normalQ dependence of the scattered spin flip intensity shows that Ce2Fe17 is not a normal paramagnetic and there exist superparamagnetic clusters of sufficiently large dimensions (~100Å). The observed neutron depolarization gives an indication of the dynamics of these Ce2Fe17 superparamagnetic clusters. 相似文献
27.
A novel PVC-based membrane sensor based on vanadyl salophen (VNSP) for determination of trace amounts of monohydrogenphosphate (MHP) ions is introduced. The electrode revealed Nernstian response towards monohydrogenphosphate over the wide concentration range from 1.0×10−1 to 1.0×10−6 M at the pH of 8.2. The effect of solvent mediator, cationic additives and amount of ion-carrier on the behavior of the sensor was investigated. The sensor shows a short response time (<20 s) in the whole concentration ranges. The selectivity of the electrode is very high, and it can be used for detection of trace amounts of monohydrogenphosphate in the presence of large amounts of other anions. The detection limit of the electrode was 5.0×10−7 M (48 ng/ml) and it could be used for 14 weeks without any measurable changes in the slope. The potentiometric selectivity coefficients data revealed negligible interference from 16 common anions. It was successfully applied for the direct determination of monohydrogenphosphate in fertilizer samples and, as an indicator electrode, in potentiometric titration of HPO42− ion with barium nitrate. 相似文献
28.
Nickel was quantitatively retained by 2-nitroso-1-naphthol-4-sulfonic acid (Nitroso-S) and tetradecyldimethylbenzylammonium chloride (TDBA Cl) onto benzophenone in the pH range 5.0-6.0 from large volumes of aqueous solutions of various samples. After filtration, each solid mass consisting of a nickel complex and benzophenone was dissolved with 5 ml of dimethylformamide (DMF) and the metal was determined by atomic absorption spectrometry (AAS). About 0.6 microg of nickel could be concentrated from 200 ml of an aqueous sample, where its concentration was as low as 3.0 ng/ml. Eight replicate determinations of 2.5 microg/ml of nickel in the final DMF solution gave a mean absorbance of 0.112 with a relative standard deviation of 1.9%. The sensitivity for 1% absorption was 98 ng/ml. The interference of a number of anions and cations was studied and the developed optimized conditions were utilized for the trace determination of nickel in various alloys and biological samples. 相似文献
29.
Mehri Javanian Mohammad Q. Vahidi-asl 《Journal of Applied Mathematics and Computing》2004,16(1-2):115-123
A recursive tree is constructed by starting with a root node and repeatedly adjoining new nodes to one node of the tree already constructed. Such a tree can represent, for example, the heirarchy of a workforce of a company that grows via recruiting. At times of economic depression, the company may decide to lay off participants, and in some cases it is a fair policy to relieve the last senior worker (most recent entry in the tree). If we remove an edge from such a tree then it falls into two subtrees one of which contains the most recent entry. If we continue to remove edges from the successively smaller subtrees that contain the most recent entry, we eventually isolate the most recent entry. We consider how many randomly selected edges must be removed in average before isolating the most recent entry by this procedure. 相似文献
30.
The analytical potential of water as an eluent in thin layer chromatographic separation of various anions on plain adsorbent layers (silica gel "G" alumina, and cellulose) as well as on beds containing different combinations of silica gel, alumina, or cellulose has been investigated. In addition to some important separation of anions, microgram separation of IO−4 from milligram quantities of IO−3, Bro−3, MoO2−4, and Fe (CN)3−6 has been realized. The effect on pH of the sample in the separation of IO−4 from accompanying ions has also been studied. The limits of detection and dilution limits of anions on alumina thin layers have been determined. NO−2 in artificial seawater has been detected. The effect of CaCl2, MgCl2, and NaHCO3 on some ternary separations of analytical importance has been examined. 相似文献