Towards an ASM thesis for reflective sequential algorithms

Starting from Gurevich's thesis for sequential algorithms (the so-called "sequential ASM thesis"), we propose a characterization of the behaviour of sequential algorithms enriched with reflection. That is, we present a set of postulates which we conjecture capture the fundamental properties of reflective sequential algorithms (RSAs). Then we look at the plausibility of an ASM thesis for the class of RSAs, defining a model of abstract state machine (which we call reflective ASM) that we conjecture captures the class of RSAs as defined by our postulates

Lead induces oxidative stress and apoptotic response in Saccharomyces cerevisiae

Background: Heavy metals are found in the environment mainly due to anthropogenic activities. The presence of metals in surface waters and soils can create an environmental hazard and pose a serious risk to public health. Lead is a non essential metal for biological functions, displays a toxic effect and is classified as probable human carcinogen. Objectives: In the present work, the mode of cell death induced by Pb in Saccharomyces cerevisiae was studied. Methods: Cell proliferation capacity was evaluated by colony-forming units counting. Membrane integrity was assessed by the fluorescent probes bis(1,3-dibutylbarbituric acid trimethine oxonol) [DiBAC4(3)] and propidium iodide. Reactive oxygen species (ROS) accumulation was examined by using 2,7-dichlorodihydrofluorescein diacetate (H2DCFDA). Nuclear morphological modifications were revealed by diaminophenylindole (DAPI) staining. Conclusions: Yeast cells, Pb-exposed, up to 6 hours, lost progressively the capacity to proliferate and maintained the membrane integrity. The exposition of yeast cells to Pb resulted in the intracellular accumulation of ROS. The addition of ascorbic acid (a ROS scavenger) strongly reduced the oxidative stress and impaired the loss of proliferation capacity in Pbtreated cells. Pb-induced death is an active process, which requires the participation of cellular metabolism, since the simultaneous addition of cycloheximide attenuated the loss of cell proliferation capacity. Pb-exposed cells displayed nuclear morphological alterations, like chromatin fragmentation. Together, the obtained data indicate that exposition of yeast cells to 1 mmol/l Pb results in a severe oxidative stress, which can be the trigger of programmed cell death by apoptosis

First-order queries on finite structures over the reals

We investigate properties of finite relational structures over the reals expressed by first-order sentences whose predicates are the relations of the structure plus arbitrary polynomial inequalities, and whose quantifiers can range over the whole set of reals. In constraint programming terminology, this corresponds to Boolean real polynomial constraint queries on finite structures. The fact that quantifiers range over all reals seems crucial; however, we observe that each sentence in the first-order theory of the reals can be evaluated by letting each quantifier range over only a finite set of real numbers without changing its truth value. Inspired by this observation, we then show that when all polynomials used are linear, each query can be expressed uniformly on all finite structures by a sentence of which the quantifiers range only over the finite domain of the structure. In other words, linear constraint programming on finite structures can be reduced to ordinary query evaluation as usual in finite model theory and databases. Moreover, if only "generic" queries are taken into consideration, we show that this can be reduced even further by proving that such queries can be expressed by sentences using as polynomial inequalities only those of the simple form x <y

Mobile Communication Device Usage: Perceptions of Non-Supervisory Employees

The increased usage of mobile communication devices (MCDs) in the workplace has been controversial regarding whether they increase or decrease productivity, whether work-life balance is affected by use, and whether employers have the right to monitor usage. This paper includes research that addressed each of these three issues linked to employee use of MCDs. Past research provided conflicting results in three areas - work-life balance, productivity, and employee monitoring. A quantitative study of 60 non-supervisory employees in Arizona, Michigan, and Illinois, consisting of an online survey, was carried out to determine perceptions of whether use of MCDs for work purposes affects work-life balance or productivity and perceptions on employers monitoring usage of work-issued MCDs. Sixty-seven percent of respondents stated that their duties require the use of MCDs and, of those 62%, each stated that his or her MCD is a Smartphone. The majority stated that Smartphones were MCDs given to them by the employer. Other MCDs were cell phones and tablets which, combined, accounted for 35% of the responses. Fifty-three percent of the respondents stated that the use of the MCD did not impact work-life balance, eighty-eight percent stated that the use of the MCD increased productivity, and eighty-seven percent stated that their employer does not monitor usage of their MCD. Research findings may vary and depend on participants. Supervisors may have different viewpoints. However, the required use of these devices in the workplace keeps increasing, so it is appropriate for employers to clearly find a benefit for their use

Incremental View Maintenance For Collection Programming

In the context of incremental view maintenance (IVM), delta query derivation is an essential technique for speeding up the processing of large, dynamic datasets. The goal is to generate delta queries that, given a small change in the input, can update the materialized view more efficiently than via recomputation. In this work we propose the first solution for the efficient incrementalization of positive nested relational calculus (NRC+) on bags (with integer multiplicities). More precisely, we model the cost of NRC+ operators and classify queries as efficiently incrementalizable if their delta has a strictly lower cost than full re-evaluation. Then, we identify IncNRC+; a large fragment of NRC+ that is efficiently incrementalizable and we provide a semantics-preserving translation that takes any NRC+ query to a collection of IncNRC+ queries. Furthermore, we prove that incremental maintenance for NRC+ is within the complexity class NC0 and we showcase how recursive IVM, a technique that has provided significant speedups over traditional IVM in the case of flat queries [25], can also be applied to IncNRC+.Comment: 24 pages (12 pages plus appendix