A distribution function for double-bit upsets

It is suggested that the chord length distribution method could be useful for predicting double-bit upset rates in certain circumstances. A chord length distribution function for simultaneous path lengths in two parallelepipeds, applicable to a unidirectional flux, is derived. A proof of the system is outlined for the case under consideration     

Structural Effects on the Adhesive Properties of Butadiene/Styrene Radial Teleblock Copolymers

The effects of butadiene/styrene ratio, monomer distribution, and molecular weight distribution and branching on the pressure sensitive adhesive properties of butadiene/ styrene radial teleblock copolymers are reported. Styrene content of polymers with varying structures shows a close relation with tack response, and styrene content and structure affect solution viscosity and shear adhesion. When part of the styrene is incorporated into the polybutadiene segment to yield a block progressively enriched in styrene (tapered block), solution viscosity and shear adhesion are reduced. When the butadiene segment is replaced by a block of randomly copolymerized butadiene and styrene, the polymers provide lower solution viscosities and shear adhesion but unchanged tack.

The molecular weight distribution of the radial teleblock polymers can vary from broad, highly branched compositions to narrow molecular weight distributions of almost Iinear polymers. The latter have relatively high solution viscosity and low shear adhesion, whereas the former polymers produce moderate solution viscosity but high shear adhesion. Tack is generally unaffected.     

Multicast Pull Scheduling: When Fairness Is Fine

Abstract. We investigate server scheduling policies to minimize average user perceived latency in pull-based client-server systems (systems where multiple clients request data from a server) where the server answers requests on a multicast/ broadcast channel. We first show that there is no O(1) -competitive algorithm for this problem. We then give a method to convert any nonclairvoyant unicast scheduling algorithm A to nonclairvoyant multicast scheduling algorithm B . We show that if A works well, when jobs can have parallel and sequential phases, then B works well if it is given twice the resources. More formally, if A is an s -speed c -approximation unicast algorithm, then its counterpart algorithm B is a 2s -speed c -approximation multicast algorithm. It is already known [5] that Equi-partition, which devotes an equal amount of processing power to each job, is a (2 + ε) -speed O(1 + 1/ε) -approximation algorithm for unicast scheduling of such jobs. Hence, it follows that the algorithm {BEQUI}, which broadcasts all requested files at a rate proportional to the number of outstanding requests for that file, is a (4 + ε) -speed O(1 + 1/ε) -approximation algorithm. We give another algorithm BEQUI-EDF and show that BEQUI-EDF is also a (4 + ε) -speed O(1 + 1/ε) -approximation algorithm. However, BEQUI-EDF has the advantage that the maximum number of preemptions is linear in the number of requests, and the advantage that no preemptions occur if the data items have unit size.     

Helicobacter pylori does not migrate from the antrum to the corpus in response to omeprazole

BACKGROUND: Omeprazole is known to have an effect on Helicobacter pylori in vivo. One opinion is that H. pylori "migrates" from the antrum to the corpus in response to omeprazole therapy. METHODS: To determine whether H. pylori migrates in response to omeprazole, we assessed the presence of H. pylori in the antrum and corpus in duodenal ulcer patients receiving omeprazole for 4 wk. Culture and histological examination of antral biopsies (Genta stain) were performed before patients received omeprazole, at the end of therapy, and 4-6 wk later. The end points were presence or absence of H. pylori and the number of H. pylori colonies per biopsy. RESULTS: Seventy-two patients had H. pylori in both the antrum and corpus at entry and 4-6 wk after ending therapy. Three general patterns were prevalent at the end of omeprazole therapy: antrum- and corpus-positive (54%), antrum-negative and corpus-positive (24%), both antrum- and corpus-negative (21%), and one patient had antrum-positive with corpus-negative (1%). Evaluation of the number of colonies per biopsy in those who remained H. pylori-positive in both the antrum and corpus throughout showed that the number of H. pylori decreased in both the antrum and corpus during therapy (507 +/- 60 vs. 225 +/- 51, p < 0.01 and 415 +/- 58 vs. 290 +/- 46 0.1) for antrum and corpus, respectively, and tended to return to pre-therapy levels 4-6 wk later. The number of H. pylori in the corpus also decreased in the antrum-negative and corpus-positive group during therapy with omeprazole (433 +/- 87 vs. 185 +/- 61, p < 0.05). In most of the patients studied, the number of H. pylori in the corpus was less posttreatment than it was pretreatment. The decrease in H. pylori load was also reflected in the development of false-negative urea breath tests. CONCLUSIONS: Omeprazole is detrimental to H. pylori in both the antrum and the corpus; migration from the antrum to the corpus in response to omeprazole is a myth.     

Speed Scaling of Processes with Arbitrary Speedup Curves on a Multiprocessor

We consider the setting of a multiprocessor where the speeds of the m processors can be individually scaled. Jobs arrive over time and have varying degrees of parallelizability. A nonclairvoyant scheduler must assign the processes to processors, and scale the speeds of the processors. We consider the objective of energy plus flow time. We assume that a processor running at speed s uses power s ^α for some constant α>1. For processes that may have side effects or that are not checkpointable, we show an W(m^(a-1)/a2)\Omega(m^{(\alpha -1)/\alpha^{2}}) bound on the competitive ratio of any randomized algorithm. For checkpointable processes without side effects, we give an O(log m)-competitive algorithm. Thus for processes that may have side effects or that are not checkpointable, the achievable competitive ratio grows quickly with the number of processors, but for checkpointable processes without side effects, the achievable competitive ratio grows slowly with the number of processors. We then show a lower bound of Ω(log ^1/α m) on the competitive ratio of any randomized algorithm for checkpointable processes without side effects.     

Communication complexity towards lower bounds on circuit depth

Karchmer, Raz, and Wigderson (1995) discuss the circuit depth complexity of n-bit Boolean functions constructed by composing up to d = log n/log log n levels of k = log n-bit Boolean functions. Any such function is in AC¹ . They conjecture that circuit depth is additive under composition, which would imply that any (bounded fan-in) circuit for this problem requires depth. This would separate AC¹ from NC¹. They recommend using the communication game characterization of circuit depth. In order to develop techniques for using communication complexity to prove circuit depth lower bounds, they suggest an intermediate communication complexity problem which they call the Universal Composition Relation. We give an almost optimal lower bound of dk—O(d ²(k log k)^1/2) for this problem. In addition, we present a proof, directly in terms of communication complexity, that there is a function on k bits requiring circuit depth. Although this fact can be easily established using a counting argument, we hope that the ideas in our proof will be incorporated more easily into subsequent arguments which use communication complexity to prove circuit depth bounds. Received: July 30, 1999.     

Mechanical properties of unidirectionally transformed Cu-In alloys

Comprehensive hardness measurements and limited tensile tests have been made on eutectoid and off-eutectoid Cu-In alloys. The alloys were transformed by unidirectional heat-treatment techniques using a range of imposed growth rates which resulted in alignment of the pearlite microstructure and a range of interlamellar spacing. Room temperature hardness of the as-transformed alloys was found to vary linearly as a function of ^–1/2, where is the pearlite interlamellar spacing; the alloys were calculated to have cooled from the decomposition temperature at rates in the range 0.047 to 18.6 K min^–1, which could result in variations of precipitation/coarsening reactions in the pearlitic phases contributing towards strength, as well as the lamellae interfaces. Hardness was also measured as a function of temperature and indicated a change in strengthening mechanism at 550 K, thought to indicate the temperature above which no significant strengthening was contributed by the pearlitic interfaces. Tensile failure of the lamellar structure occurred in a manner identical to directionally aligned Al-CuAl₂ eutectics.     

The Effect of High Temperature Thermal Cycling on Near-Surface Sulphur Partitioning in Gamma and Gamma Prime Phases and Its Implications on Sulphur Segregation in Coated Ni-Base Superalloys

Secondary ion mass spectrometry (SIMS) was used to study the near-surface segregation of sulphur during; (a) the thermal processing stages (diffusion annealing after application of Pt bond coat and after secondary ageing following subsequent deposition of the Y₂O₃-stabilised ZrO₂ top coat) and (b) thermal cycling in the Ni-base superalloy, CMSX4. In the thermal processing stages, an increased segregation of sulphur was observed within the upper regions of the Pt bond coat after diffusion annealing, while following secondary ageing, the sulphur segregation in this layer became heterogeneous with discrete pockets of enrichment (?1 ppm) and regions of depletion (?1 ppm). During thermal cycling, partitioning of sulphur occurred to the Pt-enriched γ′ region characterised by the finger-like morphology, while examination of TBC spalled specimens showed significant depletion of sulphur within the substrate in the vicinity of the surface. The reservoir for sulphur-depletion within the substrate was definitively identified as the Pt-enriched γ′ region. A quantitative method for the calculation of sulphur-segregation at the surface in terms of mono-layers is presented.