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1.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
2.
Vandana Singh Ashutosh TiwariDevendra Narayan Tripathi Tulika Malviya 《Tetrahedron letters》2003,44(39):7295-7297
O-Methylation is of outstanding importance in structural polysaccharide chemistry. A novel method for the methylation of polysaccharides using microwave (MW) irradiation is described. Seed gum from Cyamopsis tetragonolobus (Guar) was fully methylated with dimethyl sulphate and sodium hydroxide using 100% microwave power for 4 min in 68% yield. The completely methylated seed gum thus obtained was hydrolyzed by 70% formic acid followed by 0.5N H2SO4 under full microwave power for 1.16 and 1.66 min, respectively. The partially methylated monosaccharides were separated and identified. 相似文献
3.
On the departure process of a leaky bucket system with long-range dependent input traffic 总被引:2,自引:0,他引:2
Due to the strong experimental evidence that the traffic to be offered to future broadband networks will display long-range
dependence, it is important to study the possible implications that such traffic may have for the design and performance of
these networks. In particular, an important question is whether the offered traffic preserves its long-range dependent nature
after passing through a policing mechanism at the interface of the network. One of the proposed solutions for flow control
in the context of the emerging ATM standard is the so-called leaky bucket scheme. In this paper we consider a leaky bucket
system with long-range dependent input traffic. We adopt the following popular model for long-range dependent traffic: Time
is discrete. At each unit time a random number of sessions is initiated, having the distribution of a Poisson random variable
with mean λ. Each of these sessions has a random duration τ, where the integer random variable τ has finite mean, infinite
variance, and a regularly varying tail, i.e., P(τ >К) ~ К-Lα
L(К), where 1 < α < 2 L(·) is a slowly varying function. Once a session is initiated, it generates one cell at each unit of time until its termination.
We examine the departure process of the leaky bucket policing mechanism driven by such an arrival process, and show that it
too is long-range dependent for any token buffer size and any - finite or infinite - cell buffer size. Moreover, upper and
lower bounds for the covariance sequence of the output process are established. The above results demonstrate that long-range
dependence cannot be removed by the kinds of flow control schemes that are currently being envisioned for broadband networks.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
P.Veeraraghavan Ramachandran Kamlesh J Padiya Vivek Rauniyar M.Venkat Ram Reddy Herbert C Brown 《Journal of fluorine chemistry》2004,125(4):615-620
Asymmetric “allyl”boration of pentafluorobenzaldehyde with various α-pinene based “allyl”boranes provides homoallylic alcohols in high de and ee; the alcohols have been converted into δ-lactones via acryloylation, ring-closing metathesis and hydrogenation. Pentafluorophenyl analog of key pharmacophore of statin drugs has been synthesized using diastereoselective epoxidation and regioselective reduction as key steps. 相似文献
5.
R. Venkat narayan Vinod Kanniah Aruna Dhathathreyan 《Journal of Chemical Sciences》2006,118(2):179-184
Cobalt oxides were prepared by three different methods: (1) by reacting cobalt nitrate with oxalic acid, (2) co-precipitating
cobalt nitrate with sodium carbonate, and (3) using sodium dodecyl sulphate as organic surfactant. All three samples were
characterized before and after calcination by solvent extraction and the resulting products examined by IR spectroscopy. In
the case of method 3, the removal of surfactant was followed by TGA studies. Products from all three methods were identified
by XRD. Peaks in low angle XRD indicate the porous nature of the oxides. The morphology of the pores was studied by transmission
electron microscopy. Some irregular pore structures were obtained for samples from methods 1 and 2, with an average size of
4–6 nm. Only the product from method 3 using SDS as template showed ordered structure and optimum size, and Brunauer-Emmet-Teller
surface areas of the as-prepared, as well as the treated samples, exhibited H3 type hysteresis. The samples from the three
methods were used as catalysts in the oxidation reaction of cyclohexane under mild conditions and the catalytic efficiency
of the cobalt oxide was comparable with mesoporous cobalt oxides. 相似文献
6.
The deoxygenation of a variety of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones has been reported with Mg-MeOH at room temperature in nearly quantitative yields. The deoxygenation is proposed to proceed by SET from Mg to the substrate. 相似文献
7.
Synthesis and binding studies of new bis-calix[4]arenes containing aromatic and heteroaromatic units
A series of new bis-calix[4]arenes containing different aromatic and heteroaromatic moieties have been synthesized. The complexing behavior of these bis-calix[4]arenes have been studied towards different metal ions and it has been found that these bis-calix[4]arenes bind silver ions selectively over other metal ions. The complexation has been studied by liquid-liquid extraction and by NMR and IR spectroscopy. 相似文献
8.
Krishna C. Joshi Renuka Jain Anshu Dandia Vandana Sharma 《Journal of heterocyclic chemistry》1986,23(1):97-99
A novel system 2-oxo-1′,2′,4′,5′-tetrahydrospiro[3H-indole-3,3′-1,2,4,5-tetrazine]-6′-thione has been synthesized by the treatment of fluorinated isatins with thiocarbohydrazide in aqueous ethanolic medium. Under exactly similar conditions, N-acetylisatin gave exclusively thiocarbohydrazone. The spiro product, on treatment with acetic acid, gave fluorinated isoindigo. Characterization of these products have been done by elemental analyses, ir, pmr and mass spectral studies. 相似文献
9.
O,O″- and O,O′-bis(2-aminoethyl)-p-tert-butylthiacalix[4]arenes of anti conformation have been prepared by the reduction of the corresponding O,O″- and O,O′-bis(cyanomethyl) ethers. Their syn-O,O″- and O,O′-counterparts have been prepared by alternative routes via the Mitsunobu reaction of thiacalix[4]arene with N-(2-hydroxyethyl)phthalimide and the reduction of a O,O′-disiloxanediyl-bridged O″,O?-bis(cyanomethyl) ether of 1,2-alternate conformation, respectively. These products are expected to serve as useful precursors of highly elaborated synthetic receptors, including biscalixarenes. 相似文献
10.
[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin. 相似文献