The superfluid Reynolds number and the transition from potential flow to turbulence in superfluid 4^4He at mK temperatures

This comment is on Phys.Rev.Lett. 144, 155302 (2015) by M.T. Reeves, T.P. Billam, B.P. Anderson, and A.S. Bradley "Identifying a superfluid Reynolds number via dynamical similarity" where a new superfluid Reynolds number is introduced. This definition is shown to be useful in the data analysis of the finite lifetime of turbulence observed with an oscillating sphere in superfluid helium at mK temperatures in a small velocity interval $\Delta v =(v-v_c)$ just above the critical velocity $v_c$. The very rapid increase of the lifetime with increasing superfluid Reynolds number is compared with the "supertransient" turbulence observed in classical pipe flow.Comment: 3 pages, 1 figur

Understanding and Enforcing Opacity

Abstract—This paper puts a spotlight on the specification and enforcement of opacity, a security policy for protecting sensitive properties of system behavior. We illustrate the fine granularity of the opacity policy by location privacy and privacy-preserving aggregation scenarios. We present a frame-work for opacity and explore its key differences and formal connections with such well-known information-flow models as noninterference, knowledge-based security, and declassifica-tion. Our results are machine-checked and parameterized in the observational power of the attacker, including progress-insensitive, progress-sensitive, and timing-sensitive attackers. We present two approaches to enforcing opacity: a whitebox monitor and a blackbox sampling-based enforcement. We report on experiments with prototypes that utilize state-of-the-art Satisfiability Modulo Theories (SMT) solvers and the random testing tool QuickCheck to establish opacity for the location and aggregation-based scenarios. I

Crystallization of hard-sphere colloids: deviations from classical nucleation theory

The creation of three-dimensional ordered colloidal crystals, for application in a range of nanotechnologies, has been a goal for many researchers in the past few years. The main difficulty in creating macroscopic sized crystals of densely packed colloidal particles is that colloidal particles always have a range of particle sizes - ie, they are polydisperse. This paper studied the crystallization kinetics of a hard-sphere colloid with a well defined Gaussian polydispersity. The authors find that crystallization occurs in two stages, and does not follow the simple classical nucleation picture. The paper discusses the implications of these results for research into colloidal crystals as possible nano-materials

Realizing an Integrated Electronic Commerce Portal System

This experience report1 describes the design and implementation of an electronic commerce portal system for insurance companies which supports the insurance agents in their daily work. The electronic commerce portal, called IPSI, is used within an intranet. The insurance agents need information about their industrial and private customers and have to be supported in organizing their work by an organizer with reminder function, address management, etc. The insurance company has the goal to provide its employees with the most current information about its product portfolio and tariffs as well as wordings of the law and comments on it. An electronic commerce portal therefore has to provide a multitude of functions. The advantage of a portal lies in the integration of different software systems that provide these functions and thus leads the users directly to the desired information. They do not have to search awkwardly and are not served with irrelevant information. An object oriented design using UML, the realization of adequate adaptors for the integration of different heterogeneous software systems using the Java programming language, and the use of the middleware CORBA for communication within the portal were objectives of the project. This project was realized by the University of Dortmund in cooperation with different insurance and software companies. The electronic commerce portal was implemented as a prototype for a certain insurance company, including the integration of one of their legacy systems

Small changes in particle-size distribution dramatically delay and enhance nucleation in hard sphere colloidal suspensions

We present hard-sphere crystallization kinetics for three samples with small differences in polydispersity. We show that an increase in polydispersity of 1% is sufficient to cause dramatic changes in the crystallization kinetics: Crystallization is delayed by almost one decade in time and quantitative and qualitative changes in the crystallization scenario are observed. Surprisingly the nucleation rate density is enhanced by almost a factor of 10. We interpret these results in terms of polydispersity limited growth, where local fractionation processes lead to a delayed but faster nucleation

Flexible Information-Flow Control

As more and more sensitive data is handled by software, its trustworthinessbecomes an increasingly important concern. This thesis presents work on ensuringthat information processed by computing systems is not disclosed to thirdparties without the user\u27s permission; i.e. to prevent unwanted flows ofinformation. While this problem is widely studied, proposed rigorousinformation-flow control approaches that enforce strong securityproperties like noninterference have yet to see widespread practical use.Conversely, lightweight techniques such as taint tracking are more prevalent inpractice, but lack formal underpinnings, making it unclear what guarantees theyprovide.This thesis aims to shrink the gap between heavyweight information-flow controlapproaches that have been proven sound and lightweight practical techniqueswithout formal guarantees such as taint tracking. This thesis attempts toreconcile these areas by (a) providing formal foundations to taint trackingapproaches, (b) extending information-flow control techniques to more realisticlanguages and settings, and (c) exploring security policies and mechanisms thatfall in between information-flow control and taint tracking and investigating whattrade-offs they incur