A feedback fluid queue with two congestion control thresholds

Feedback fluid queues play an important role in modeling congestion control mechanisms for packet networks. In this paper we present and analyze a fluid queue with a feedback-based traffic rate adaptation scheme which uses two thresholds. The higher threshold B ₁ is used to signal the beginning of congestion while the lower threshold B ₂ signals the end of congestion. These two parameters together allow to make the trade-off between maximizing throughput performance and minimizing delay. The difference between the two thresholds helps to control the amount of feedback signals sent to the traffic source. In our model the input source can behave like either of two Markov fluid processes. The first applies as long as the upper threshold B ₁ has not been hit from below. As soon as that happens, the traffic source adapts and switches to the second process, until B ₂ (smaller than B ₁) is hit from above. We analyze the model by setting up the Kolmogorov forward equations, then solving the corresponding balance equations using a spectral expansion, and finally identifying sufficient constraints to solve for the unknowns in the solution. In particular, our analysis yields expressions for the stationary distribution of the buffer occupancy, the buffer delay distribution, and the throughput.     

EPR spectrum of gadolinium in hydrated praseodymium sulphate

The electron paramagnetic resonance of Gd³⁺ in single crystal of Pr₂(SO₄)₃.8H₂O is studied at room temperature. Two magnetic complexes exhibiting orthorhombic or lower symmetry are found and the results have been fitted to a suitable spin Hamiltonian. The exact solution of Hamiltonian matrix is carried out and 10 “best fit” parameters are obtained using iterative optimization technique. The zero field splittings of Gd³⁺: Pr₂(SO₄)₃.8H₂O have been computed. Few forbidden transitions are observed and explained using numerical solution of the Hamiltonian matrix.     

Label Free Colorimetric Biosensing Using Nanoparticles

In this review article, we discuss a class of biosensors that exploit the change in the colorimetric properties of noble metal nanoparticles in response to biomolecular binding at their surface. Several sensor fabrication techniques as well as sensor configurations are discussed with an emphasis on their strengths and limitations. We conclude by presenting the future prospects and challenges for the successful transition of this technology from the laboratory to a commercial product.     

Polymerization of α-Methylstyrene in p-Dioxane with Potassium as Initiator. III. Gel-Permeation Chromatographic Analyses of Polymers

Gel-permeation chromatographic studies on poly-α-methyl-styrene initiated with potassium and potassium-naphthalene in p-dioxane as solvent and polymerized at 5, 15, 25, and 40°C, have been carried out. Bimodal and trimodal distributions are observed in these polymers. It has been shown that these multimodal distributions do not arise because of the monofunctional and bifunctional living ends produced by the reaction of solvent dioxane with the living polymer. These, on the other hand, may be related to the presence of different ion-pairs which contribute to the reaction but to different extents. Contrary to the belief that only contact ion-pairs are responsible for propagation in p-dioxane because of its low dielectric constant, the presence of solvent-separated ion-pairs yielding reversible propagation has been speculated. The different components (D + A), B, and C, similar to the ones present in the a-methyl-styrene-potassium tetrahydrofuran system, have been found in the present study also and are attributed to the dead and a dormant polymer, solvent-separated ion-pair polymer, and that due to a contact pair, respectively. The extent of the formation of component (D + A) has been linked directly to the concentration of living ends. In reactions where naphthalene was used along with potassium for initiation purposes, a unique component yielding reversible propagation was observed. This has been attributed to the presence of polymer due to potassium-naphthalene complex which is different in character to a contact ion-pair but may resemble a solvent-separated ion-pair.     

Inelastic cross sections for pentane isomers by positron impact

ABSTRACT

This work aims at the calculation of various inelastic cross sections for three pentane isomers, namely normal pentane, isopentane and neopentane. The direct ionisation, positronium formation, total ionisation and total inelastic cross section are reported for these targets using modified spherical complex optical potential (mSCOP) and complex scattering potential-ionisation contribution (CSP-ic) method. The cross sections are computed for a wide energy range from their respective thresholds to 5?keV. We have also attempted to probe the isomeric effect in the inelastic scattering of positrons from the pentane isomers. The cross sections for the three isomers were found to overlap for the entire comparative energy range except at the peak region. Hence, in general no appreciable isomeric effect was beheld for the pentane isomers.     

An expedient protocol for conversion of olefins to α-bromo/iodoketones using IBX and NBS/NIS

A variety of olefins have been shown to undergo conversion to the corresponding α-bromo/iodoketones when reacted with NBS/NIS and IBX in DMSO at room temperature. While the reaction is found to occur rapidly with e-rich arylolefins leading to the corresponding haloketones in 65-95% yields in 0.3-3.0 h, those containing e-withdrawing groups are found to yield diketones concomitantly, such that the latter are the exclusive products over extended duration of the reactions.