Queueing at large resources driven by long-tailed M/G/∞-modulated processes

We analyze the queue at a buffer with input comprising sessions whose arrival is Poissonian, whose duration is long-tailed, and for which individual session detail is modeled as a stochastic fluid process. We obtain a large deviation result for the buffer occupation in an asymptotic regime in which the arrival rate nr, service rate ns, and buffer level nb are scaled to infinity with a parameter n. This can be used to approximate resources which multiplex many sources, each of which only uses a small proportion of the whole capacity, albeit for long-tailed durations. We show that the probability of overflow in such systems is exponentially small in n, although the decay in b is slower, reflecting the long tailed session durations. The requirements on the session detail process are, roughly speaking, that it self-averages faster than the cumulative session duration. This does not preclude the possibility that the session detail itself has a long-range dependent behavior, such as fractional Brownian motion, or another long-tailed M/G/∞ process. We show how the method can be used to determine the multiplexing gain available under the constraint of small delays (and hence short buffers) for multiplexers of large aggregates, and to compare the differential performance impact of increased buffering as opposed to load reduction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Critical flow in a chemically reacting two-phase multicomponent mixture

A model that describes the critical flow of chemically reacting, two-phase, multicomponent mixtures in channels of constant cross section is discussed. As a consequence of an assumed interphase thermal and mechanical equilibrium the applicability of the model is restricted to situations where one phase is intimately mixed with the other, such that choking is determined by the sound speed in the homogeneous mixture. It is shown that under certain conditions the highly non-linear temperature dependency of the reaction rate promotes the possibility of a multiplicity of steady state solutions to the problem.     

Citronellyl citronellate and citronellyl geranate in the European hornet, vespa crabro (hymenoptera: vespidae)

Citronelly citronellate and citronellyl geranate, new insect natural products, have been identified in the van der Vecht's gland of the European hornet.     

Thermodynamics of the BCS model through large deviations

Using large deviations in combination with the Berezin-Lieb inequalities, we analyse the phase-transition in the BCS model with nonconstant energies and interactions.     

Mass spectrometry in structural and stereochemical problems—CLXXI: Factors governing the preferential loss of small vs. Large radicals in the α-fission of aliphatic amines

A study of the α-cleavage processes of aliphatic amines (using R_LCH₂N(R)CH₂R_s and R_LCH(NR)R_s

1 R_L represents the larger R_s the smaller alkyl group throughout this paper and both, unless indicated to the contrary, have similar degrees of lsubstitution on the α-carbon atom.

as typical substrates) at several ionizing voltages indicates that the loss ratio of large and small alkyl radicals, [M ? R_L]/[M ? R_s], decreases with ionizing voltage. This ratio, greater than 1·0 at 70 eV, may become less than unity at low voltage (15 eV, 10 eV) in some cases. Comparison of similarly structured compounds with nitrogen or oxygen as the heteroatom suggests that the effects of ionizing voltage are lessened when the fragment is of greater stability (e.g. amine vs. ether or imine vs. ketone). The effects of lowering the ionizing voltage became much less pronounced as the alkyl groups become larger or similar in size.     

Exponential bounds for queues with Markovian arrivals

Exponential bounds [queueb]e ^b are found for queues whose increments are described by Markov Additive Processes. This is done by application of maximal inequalities to exponential martingales for such processes. Through a thermodynamic approach the constant is shown to be the decay rate for an asymptotic lower bound for the queue length distribution. The class of arrival processes considered includes a wide variety of Markovian multiplexer models, and a general treatment of these is given, along with that of Markov modulated arrivals. Particular attention is paid to the calculation of the prefactor .     

Further studies on a site-specific hydrogen transfer observed in electron capture negative ion chemical ionization mass spectrometry of hydroxyamine pentafluoropropionate derivatives

Further studies have demonstrated that the site-specific hydrogen transfer process involved in the formation of the m/z 145 anion of β-hydroxyamine pentafluoropropionate (PFP) derivatives observed under electron capture negative ion chemical ionization conditions occurs when the two functional groups are separated by up to five carbon atoms. Deuterium labelling has established that the site specificity, transfer of a hydrogen atom from the carbon adjacent to nitrogen to the OPFP group, is maintained in 4-amino-butan-1-ol-N, O-(PFP)₂. The corresponding PFP derivatives of the N-methylaminoalkanol-(PFP)₂ derivatives lack the m/z 145 species with m/z 163, [OPFP]^? being the base anion. Substitution of alkyl groups on the carbon adjacent to oxygen results in a diminution of the ion intensity at m/z 145. with a marked increase in the intensity of m/z 144. The formation of the m/z 145 and 144 anions to proposed to proceed through the intervention of a fluoride ion-molecule complex as outlined in Scheme 1 with the product ion distribution dependent on which of the two pathways is preferred.     

Electron-impact induced fragmentation of some natural products containing bis-2,2-dimethylchromene and bis-2,2-dimethylchroman ring systems

Derivatives of eriostoic and eriostemoic acids (II and III) and their tetrahydro analogs (VI and IX) which contain the bis-2,2-dimethylchromene and the bis-2,2-dimethylchroman ring systems respectively, fragment subsequent to electron-impact in characteristic fashion. The former yield mass spectra dominated by the loss of a methyl radical from their molecular ions while the latter exhibit preferential fragmentation of the heterocyclic ring system. In particular the hydrogen transfer process accompanying elemination of C₄H₇ from the parent ion of bis-2,2-dimethylchromans was investigated by deuterium labeling studies. Fragment ions containing the bis-2,2-dimethylchroman ring undergo further fragmentation by the loss of C₄H₈ rather than C₄H₇. An unusual elimination of CH₅ (accompanied by the appropriate metastable ion) from the molecular ions of the 3,5-dinitrobenzoate esters (XIV and XV) was observed in their mass spectra.     

Fatigue test of a three-span composite bridge

The feasibility of conducting a fatigue test on an existing three-span continuous composite highway bridge has been evaluated. An analytical study, in which the bridge was treated as a multi-degree of freedom system, showed that critical fatigue zones occur in the girder flanges within the end spans. The base metal under the top-flange shear connectors between a field splice and the end of a cover plate, and the base metal at the end of a cover plate in the top and bottom flanges, are susceptible to fatigue failure. This anticipated test behavior simulates the concern of the current AASHO Specifications. The sustained stress levels will be equal to the design live load plus impact stresses. Fatigue failure is probable within 600,000 cycles at a stress range of approximately 14 ksi (96×10⁶ Pa). A series of steady-state resonance tests were conducted on a single-span composite model to assess the practicability of the proposed fatigue-testing technique. These laboratory tests verified that an electrohydraulic actuator with an attached weight would perform satisfactorily as a loading device to induce resonant vibrations. The performance of the bridge-shaker system was analyzed to insure the capability of this technique to produce the required stress levels for the fatigue test on the prototype bridge. The test was scheduled for the summer of 1975.