Modeling of precipitation hardening in Mg-based alloys

This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved by precipitation of binary phases such as MgZn₂ and Mg₂Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’ evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters of the model, R _N i and k _{σ i} , were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated from the hardness maximum positions on the aging curves.     

Logical diagnosis ofLDL programs

The debuggers of Ref. 11) and most of their derivatives are of themeta-interpreter type. The computation of the debugger tracks the computation of the program to be diagnosed at the level of procedure call. This is adequate if the intuitive understanding of the programmer is in terms of procedure calls; as is indeed the case in Prolog. InLDL however, while the semantics of the language are described in a bottom-up, fixpoint model of computation,⁸⁾ theactual execution of a program is a complex sequence of low-level procedure calls determined (and optimized) by the compiler. Consequently, a trace of these procedure calls is of little use to the programmer. Further, one cannot “execute” anLDL program as if it was a Prolog program; the program may simply not terminate in its Prolog reading and severalLDL constructs have no obvious Prolog counterparts. We identify the origin of a fault in theLDL program by a top-down, query/subquery approach. The basic debugger, implemented in Prolog, is a shell program between the programmer and theLDL program: it poses queries and uses the results to drive the interaction with the user. It closely resembles the one presented in Ref. 11). The core of a more sophisticated debugger is presented as well. Several concepts are introduced in order to quantify debugging abilities. One is that of agenerated interpretation, in which the structureless intended interpretation of Ref. 11) is augmented with causality. Another is the (idealized) concept of areliable oracle. We show that given an incorrect program and a reliable oracle which uses a generated interpretation, a cause for the fault will be found in finitely many steps. This result carries over to the more sophisticated debugger.     

Task Switching After Cerebellar Damage.

The authors of this study investigated task switching following cerebellar damage. The study group consisted of 7 children and adolescents (M age = 13.8 years) who underwent surgical removal of a benign posterior fossa tumor. They were tested at a sufficient interval after surgery (M lag = 6.13 years) for restoration of normal cognitive skills and intelligence. Although all showed normal learning of the task compared with control participants, when rapid behavioral changes were required (short preparation time), they exhibited behavioral rigidity manifested by enhanced switching cost. These results are in line with another study on serial reaction time with the same patients (A. Berger et al., in press). They have important implications for our understanding of the cognitive sequelae of early cerebellar damage as well as the involvement of the cerebellum in task switching. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Turned trochoidal disturbance on a liquid jet surface

This paper shows that a turned trochoidal function disturbance may lead to peripheral drops production. The resulting model is used to describe that a turned trochoidal disturbance leads to peripheral drops production on the liquid jet surface without the necessity for superimposed disturbances. The trochoid is a non-unique parametric function. Only non-unique parametric functions disturbances may lead to peripheral drops production. The trochoidal function disturbance is decomposed to Fourier series. Every Fourier element receives an amplification factor in accordance to the Rayleigh inviscid jet model. Peripheral drops are received on the jet surface. The paper shows that all trochoidal disturbance functions, prolate cycloid, cycloid and curtate cycloid have a capability of peripheral drops producing. A limited capability of peripheral drops production is introduced for the trochoidal curtate cycloid. Produced drops size are reduced for increasing the jet velocity and wave number. Smaller drops are also received by transition from the prolate cycloid to curtate cycloid disturbance.     

Applications,Enrollment, Attendance,and Student Performance in Rebuilt School Facilities: A Case Study

Public school construction represents a significant portion of all construction spending in the United States; yet, the average age of United States’ public schools is 42 years old. This article focuses on magnet schools in a large urban school district in the United States. The study examines whether construction, building age, and building condition have an impact on magnet applications, enrollment, attendance, and student achievement measures. Twenty-eight magnet elementary schools in the school district were chosen for analysis. The experimental group (n=14) included all magnet elementary schools (kindergarten to 5^th grade [K-5]) rebuilt under three school bond programs. The control group (n=14) included randomly selected elementary schools (K-5) from the 32 remaining elementary schools in the district that were not rebuilt. Multiple regressions were conducted using building and student data gathered during the 2011-2012 school year. Results indicate that building composite score and building age had no observable predictive effects on magnet applications, student enrollment, or student attendance, in both groups. However, student achievement was positively affected by building composite score as measured by the ability to predict state percentile ranking. This study supports that building and maintaining high quality educational facilities has the potential to raise student achievement levels.     

Synthesis of N-Alkyl-α-Sulfo-β-Alanines

A number of N-alkyl substituted α-sulfo-β-alanines were synthesized by direct sulfonation of the corresponding N-alkyl-β-alanines.     

Domain-structured N1,N2-derivatized hydrazines as inhibitors of ribonucleoside diphosphate reductase: redox-cycling considerations

Eight analogues of 1-[5-halogenosalicylidene]-2-[2'-pyridinoyl]hydrazine and -[2'-pyridyl]hydrazine, four of 1-[pyridoxylidene]-2-[2'-pyridinoyl]hydrazine, seven of 1-[pyridoxylidene]-2-[2'-pyridyl]hydrazine, and one each of 1, 2-bis[pyridoxylidene]diaminoethane and bis[pyridoxylidenehydrazino]phthalazine were synthesized. Their solutions in DMF were assayed for activity against the metalloenzyme ribonucleoside diphosphate reductase (RdR), prepared from a subcutaneously growing murine tumor (sarcoma 180) implanted in B6D2F3 male mice. The 14C-labeled CDP reductase was assayed by the modified method of Takeda and Weber, in which [14C]cytidine was separated from deoxycytidine by thin-layer chromatography (TLC) on cellulose foil. Distribution of radioactivity was assessed with an automatic TLC linear analyzer. Of the 31 compounds tested, 13 were essentially inactive, 7 were highly active against RdR, and the remaining 20 were slightly more active than hydroxyurea (used as a reference compound). The mechanism of inhibition is discussed in terms of three alternative pathways, initiated by sequestration of iron embedded in the R1 subunit of the metalloenzyme to form a C-centered chelate radical (via redox cycling). Alternatively, the latter could either reduce the tyrosyl radical or intercept radicals generated in the reduction process.     

The Synthesis,Crystal and Molecular Structure,and Oxidation State of Iron Complex from Pyridoxal Isonicotinoyl Hydrazone and Ferrous Sulphate

The reaction of isonicotinoyl hydrazone of pyridoxal (PIH), a biologically active iron-carrier, with FeSO₄-7H₂0 at pH ∼ 6 generates the delta, lamda species of the N,N-trans-O,O-cis-cis coordination isomer of an iron(III) complex with iron-to-ligand ratio of 1:2. The dark red-brown crystals are monoclinic, space group C2/c, with unit-cell dimensions a = 14.487(2), b = 18.586(2), c = 27.508(4) Å, β = 102.76(3)°, and Z = 8. The coordination around the metal is distorted octahedral and involves the protonated organic ligands, which are chelated through the phenolic oxygen [Fe-O1 1.941(6), Fe-O1′ 1.938(6)], an enolic form of the carbonyl oxygen [Fe-O3 2.017(6), Fe-O3′ 2.018(6)] and the azomethinic nitrogen [Fe-N2 2.133(8), Fe-N2′ 2.133(8)]. Packing is determined by systems of N-H….O and O-H….O hydrogen bonds involving the protonated pyridoxal nitrogens, the pyridoxal hydroxymethyl group, and the [SO₄]²⁻ group. The Mössbauer spectra at different temperatures (300 K, 88 K and 4.1 K) clearly prove that the iron atom in the complex is in a high-spin trivalent state.     

Identification of parameters for embodied energy measurement: A literature review

The building construction industry consumes a large amount of resources and energy and, owing to current global population growth trends, this situation is projected to deteriorate in the near future. Buildings consume approximately 40 percent of total global energy: during the construction phase in the form of embodied energy and during the operation phase as operating energy. Embodied energy is expended in the processes of building material production (mining and manufacture), on-site delivery, construction and assembly on-site, renovation and final demolition. Recent studies have considered the significance of embodied energy inherent in building materials, with a specific focus on this fraction of sequestered energy. Current interpretations of embodied energy are quite unclear and vary greatly, and embodied energy databases suffer from problems of variation and incomparability. Furthermore, there is no reliable template, standard or protocol regarding embodied energy computations that could address these problems in embodied energy inventories. This paper focuses on the analysis of existing literature in order to identify differing parameters so that development of a consistent and comparable database can be facilitated.