N.m.r. line shape-relaxation correlation analysis of bitumen and oil sands

The first results of the analysis of bitumen and oil sands using the recently developed n.m.r. spingrouping technique are presented. The n.m.r. relaxation experiments were carried out on bitumen, and on natural and dried oil sands samples. The results indicate that the spin-grouping can resolve and quantify several components of the samples studied. The bitumen and bitumen fraction of the oil sands are resolved according to their spin-spin relaxation times into three major groups: solid-like (rigid), solid-like (mobile) and semi-liquid. The water in the oil sands exists in two different environments. Tentatively one environment is assigned to be the bridges between the sand grains, while the other is assigned to be the clay surface. One can conclude that with spin grouping of complex mixtures the decomposition (in which components are resolved according to their dynamic state) is possible. The accuracy of such resolution is of the order of a few per cent.     

Cryptography and cryptographic protocols

We survey the paradigms, approaches and techniques used to conceptualize, define and provide solutions to natural cryptographic problems. We start by presenting some of the central tools (e.g., computational difficulty, pseudorandomness, and zero-knowledge proofs), and next turn to the treatment of encryption and signature schemes. We conclude with an extensive treatment of secure cryptographic protocols both when executed in a stand-alone manner and when many sessions of various protocols are concurrently executed and controlled by an adversary. The survey is intended for researchers in distributed computing, and assumes no prior familiarity with cryptography.Received: June 2001, Accepted: July 2002,     

The secondary structure of phospholamban: a two-dimensional NMR study

Phospholamban (PLN) is an intrinsic membrane protein of 52 amino acids which regulates the Ca2+ pump of the sarcoplasmic reticulum of heart, slow-twitch and smooth muscle (SR): it is normally assumed to exist in the membrane as a homopentamer. A monomeric analogue of phospholamban PLN(C41F), in which Cys41 was replaced by a Phe, was synthesized and its conformation studied by 1H NMR spectroscopy in a 1:1 mixture of chloroform/methanol. Most of the resonances in the 1H NMR spectra were assigned. The work has shown that the C-terminal hydrophobic portion forms a very stable alpha-helix. The hydrophilic N-terminal part adopts an alpha-helix configuration which is much less stable except for the stretch containing the phosphorylation sites.     

Almost k-wise independence versus k-wise independence

We say that a distribution over {0,1}ⁿ is (ε,k)-wise independent if its restriction to every k coordinates results in a distribution that is ε-close to the uniform distribution. A natural question regarding (ε,k)-wise independent distributions is how close they are to some k-wise independent distribution. We show that there exist (ε,k)-wise independent distributions whose statistical distance is at least n^O(k)·ε from any k-wise independent distribution. In addition, we show that for any (ε,k)-wise independent distribution there exists some k-wise independent distribution, whose statistical distance is n^O(k)·ε.     

Products Used to Secure Networked Macintosh Computers

Abstract

Service-oriented architectures (SOAs) have become mainstream in the past year due to their ability to provide business agility and flexibility through integration, productivity, and software reuse. The Web services framework enables composite applications that leverage service- oriented architecture (SOA) design practices, creating more cost-effective distributed architectures. As enterprises adopt SOA, they open their systems, enabling greater agility and easier integration.     

Open source content contributors’ response to free-riding: The effect of personality and context

We address concerns about the sustainability of the open source content model by examining the effect of external appropriation, whereby the product of open source contributors’ efforts is monetized by a party that did not contribute to the project, on intended effort withdrawal (reduction in contribution level). We examine both the personality of contributors and their contextual motivations to contribute, using a scenario-based survey of Wikipedia contributors. The findings suggest that perceived justice of the open source license terms, and intrinsic motivations are both negatively related with effort withdrawal intentions. Moreover, we find that the effect of the fairness personality trait on effort withdrawal is stronger for individuals who are low in perceived justice and weaker for individuals high in justice. The findings of factors predicting effort withdrawal contribute to the open source literature, which tends to focus on contribution and motivations, but not on what impacts changes in individual contribution levels.     

Geometric Bone Modeling: From Macro to Micro Structures

There is major interest within the bio-engineering community in developing accurate and non-invasive means for visualizing, modeling and analyzing bone micro-structures. Bones are composed of hierarchical bio-composite materials characterized by complex multi-scale structural geometry. The process of reconstructing a volumetric bone model is usually based upon CT/MRI scanned images. Meshes generated by current commercial CAD systems cannot be used for further modeling or analysis. Moreover, recently develop...     

Optimal search path for service in the presence of disruptions

We consider the following basic search path problem: a customer residing at a node of a network needs to obtain service from one of the facilities; facility locations are known and fixed. Facilities may become inoperational with certain probability; the state of the facility only becomes known when the facility is visited. Customer travel stops when the first operational facility is found. The objective is to minimize the expected total travel distance.     

On the complexity of approximating k-set packing

Given a k-uniform hypergraph, the Maximum k -Set Packing problem is to find the maximum disjoint set of edges. We prove that this problem cannot be efficiently approximated to within a factor of unless P = NP. This improves the previous hardness of approximation factor of by Trevisan. This result extends to the problem of k-Dimensional-Matching.