An integrated systems biology approach to understanding the rules of keratinocyte colony formation.

Closely coupled in vitro and in virtuo models have been used to explore the self-organization of normal human keratinocytes (NHK). Although it can be observed experimentally, we lack the tools to explore many biological rules that govern NHK self-organization. An agent-based computational model was developed, based on rules derived from literature, which predicts the dynamic multicellular morphogenesis of NHK and of a keratinocyte cell line (HaCat cells) under varying extracellular Ca++ concentrations. The model enables in virtuo exploration of the relative importance of biological rules and was used to test hypotheses in virtuo which were subsequently examined in vitro. Results indicated that cell-cell and cell-substrate adhesions were critically important to NHK self-organization. In contrast, cell cycle length and the number of divisions that transit-amplifying cells could undergo proved non-critical to the final organization. Two further hypotheses, to explain the growth behaviour of HaCat cells, were explored in virtuo-an inability to differentiate and a differing sensitivity to extracellular calcium. In vitro experimentation provided some support for both hypotheses. For NHKs, the prediction was made that the position of stem cells would influence the pattern of cell migration post-wounding. This was then confirmed experimentally using a scratch wound model.     

GaAs planar-doped barrier vacuum microelectronic electron emitters

A novel vacuum microelectronic electron emitter has been demonstrated in GaAs by using a planar-doped-barrier (PDB) structure. Emitted electrons are collected in high vacuum by a tantalum anode placed ~1 mm away from the emitter surface. Surface passivation with (NH ₄)₂S_x followed by in situ heating in vacuum has been used to obtain an atomically clean surface. An emission current density of 0.42 A-cm^-2 and an efficiency of 0.3% have been obtained from a 60 μm×60 μm emission region with an anode bias of 100 V     

PX systems = P systems + X machines

The paper is a survey of the main features of P systems, X machines and of a new computational device called PX system. The sequential and the parallel PX systems are presented. Results reflecting the computational power of these models and their effectiveness in solving NP-complete problems are briefly mentioned.     

An Integrated Refinement and Testing Method for Stream X-machines

 Over the last decade, stream X-machines have been used in order to specify a range of systems. One of the strengths of this approach is that, under certain well defined conditions, it is possible to produce a test set that is guaranteed to determine the correctness of the implementation under test. However, if X-machines are to be used in practice as a tool for specification and test generation, there needs to be ways of developing existing specifications into more complex and more detailed versions through a process of refinement. Associated with the refinement of the specification, there needs to be methods of refining the corresponding test sets, that is to construct the test set in parallel with the specification and to distribute the testing into smaller chunks, with major cost and time savings. A few such specification and testing refinements of X-machine have already been investigated. This paper introduces a new type of X-machine refinement, called simple covering, which expands the input-output behaviour of an existing X-machine. Associated with this process, the corresponding refinement of the test set is described and a method of testing X-machines constructed as simple coverings is developed. Received: March 29, 2000; revised version: December 2, 2001     

Lessons learned about service quality: What it is, how to manage it, and how to become a service quality organization.

Discusses lessons that the authors' experiences in the area of service quality have taught them about how to help a business develop into the kind of company that can deliver quality service to its customers. A theme running through the article is that becoming such a company is a multistage process that involves coordinating changes in many facets of organizational functioning. Furthermore, it is repeatedly emphasized that the design of these facets must be aligned with the market sector the organization wants to target. Lessons 1, 2, and 3 address the implications of service marketing, operations management, and human resources management for delivering quality service. The integration of what has been learned in these 1st 3 lessons is the topic of Lesson 4: creating a climate and a culture for service. Finally, some practical suggestions and guidelines are offered for beginning the process of becoming a service organization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison and evaluation of the synthetic biopolymer poly-L-aspartic acid and the synthetic "plastic" polymer poly-acrylic acid for use in metal ion-exchange systems

Poly-L-aspartic acid (PLAsp), a biopolymer, and a similar synthetic polymer, poly-acrylic acid (PAA), each consisting of approximately 50 repeating Asp and acrylic acid monomers, respectively, were immobilized onto controlled pore glass (CPG) and evaluated for use as metal ion-exchange materials. Both polymers achieve metal complexation primarily through their repeating carboxylate side groups resulting in a similar binding trend for the metals tested (Ca(2+), Cd(2+), Co(2+), Cu(2+), Mg(2+), Mn(2+), Na(+), Ni(2+), Pb(2+)), with metal binding capacities ranging from <0.1 to 12 micromol metal/g column and <0.1 to 32 micromol metal/g column for PLAsp and PAA respectively. Cu(2+) and Pb(2+) exhibited strong binding to both materials, while the other metals demonstrated only weak or minimal binding. Both columns allowed for quantitative release of bound metals through acid stripping and experienced increased overall metal binding with increasing pH. Both systems also maintained similar structural and chemical stability when continuously exposed to neutral buffered, highly acidic, oxidizing, large molecule rich, and elevated temperature environments. The main differences between the two systems are the material cost and system biodegradability.     

Testing (Stream) X-machines

In 1988 X-machines were proposed as a basis for a specification language and, since then, a number of further investigations have demonstrated the value of this idea. A number of classes of X-machines have been identified and studied, most importantly the class of stream X-machines. A theory of testing based on stream X-machines has also been developed. This allows the generation of test sets which, if satisfied, guarantee, under certain constraints, the correctness of implementation with respect to specification. This paper extends this theory in two ways. Firstly, it considers the general X-machine model rather than the particular stream X-machine class. Secondly, the theoretical results proved give rise to at least two different testing strategies. These results are then particularised to the stream X-machine class. Key words:Testing, Finite state machine, (stream) X-machine, Formal specification.     

Efficient small molecule bulk heterojunction solar cells with high fill factors via pyrene-directed molecular self-assembly

Efficient organic photovoltaic (OPV) materials are constructed by attaching completely planar, symmetric end-groups to donor-acceptor electroactive small molecules. Appending C2-pyrene as the small molecule end-group to a diketopyrrolopyrrole core leads to materials with a tight, aligned crystal packing and favorable morphology dictated by π-π interactions, resulting in high power conversion efficiencies and high fill factors. The use of end-groups to direct molecular self-assembly is an effective strategy for designing high-performance small molecule OPV devices.