Towards biomimetic models of the reduced [FeFe]-hydrogenase that preserve the key structural features of the enzyme active site; a DFT investigation

[FeFe]-hydrogenases are the most efficient biological catalysts available for the H₂ evolution reaction. Their active site – the H-cluster – features a diiron subsite which has the peculiar characteristic of bearing cyanide groups hydrogen-bonded to the apoprotein as well as carbonyl ligands. Notably, one of the CO ligands is disposed in bridging position between the metal centers. This allows one of the Fe ions to retain a square pyramidal coordination – which determines the assumption of the so-called “rotated structure” – with a vacant coordination site in trans to the μ-CO group, ready to bind protons when the active site is in the Fe^IFe^I state. Many Fe^IFe^I biomimetic models have been synthesized and characterized so far, but most of them fail to reproduce the orientation of the diatomic ligands that is observed in the enzyme active site.     

Options and overbooking strategy in the management of wireless spectrum

Dynamic spectrum management makes it possible for the owner of usage rights on some frequency blocks to sublet each of them in real time and for a limited period of time. As a softer implementation with respect to the spot market a two stage assignment is here proposed through the use of options, which give buyers the right to purchase the usage right on a single block and for a timeslot. In the sale of options the primary owner may accomplish an overbooking strategy, which consists in selling more blocks than the available ones, and acts as a hedging tool against the risk of unsold blocks. A model for the overbooking strategy is described and evaluated, which takes into account both the value of the option, the correlated decisions taken by the prospective purchasers, and the penalty to be paid to the unsatisfied customers. The dependence of the economical convenience of the overbooking strategy on the relevant parameters (among which the penalty value and the overbooking ratio) is shown for a significant range of cases.     

Innovative travel time model for dual-shuttle automated storage/retrieval systems

In modern production and distribution systems, the automated storage/retrieval systems (AS/RS), high-storage level systems that reduce labor cost, required floor space and error rate, while increasing product availability, have been widely used since the 1950s. Due to the high-investment costs involved in the development of high-efficient and high-flexible automated storage systems, performance estimation of the systems is both practically and theoretically important. The authors suggest a new method to estimate the travel time of a recently emerging version of AS/RSs, the multi-shuttle systems. The proposal is based on an industrial standard established by the Federation Européenne de la Manutention (F.E.M.). In order to estimate travel times, the authors conduct a Monte Carlo simulation to determine coordinates of two additional representative points which are not given by F.E.M. Then they conduct a new Monte Carlo simulation to compare the results obtained by the method they proposed with those of previous methods and models developed in scientific literature based on Bozer and White formulations. Several real industrial applications demonstrate the validity of proposed method.     

A comparative evaluation of nonlinear dynamics methods for time series prediction

A key problem in time series prediction using autoregressive models is to fix the model order, namely the number of past samples required to model the time series adequately. The estimation of the model order using cross-validation may be a long process. In this paper, we investigate alternative methods to cross-validation, based on nonlinear dynamics methods, namely Grassberger–Procaccia, Kégl, Levina–Bickel and False Nearest Neighbors algorithms. The experiments have been performed in two different ways. In the first case, the model order has been used to carry out the prediction, performed by a SVM for regression on three real data time series showing that nonlinear dynamics methods have performances very close to the cross-validation ones. In the second case, we have tested the accuracy of nonlinear dynamics methods in predicting the known model order of synthetic time series. In this case, most of the methods have yielded a correct estimate and when the estimate was not correct, the value was very close to the real one.     

Loss of ascorbic acid during storage of Conference pears in relation to the appearance of brown heart

To investigate the causes of brown heart (BH) in Conference pears, the contents of ascorbic acid (AA) and dehydroascorbic acid (DHAA) in fruits were studied during the first period of storage. AA was studied in 1999 and 2000, DHAA in 1999 only. Pears from normal and very late harvest stored immediately or after a delay in a controlled atmosphere with 2% O₂ and low (0.7%) or high (5%) CO₂ were compared. DHAA content did not change during storage in any treatment. AA decreased in storage according to an exponential model. The rate of AA loss was different in the two years and was higher in late‐harvest fruits and in those stored in 5% CO₂. BH appeared in different treatments when AA decreased below a threshold, which was about 2 mg kg^?1 fresh weight, corresponding to 5% of the AA content at harvest. The frequency and severity of symptoms depended linearly on the time spent by fruits in low‐ascorbate conditions. Advanced maturity at harvest and storage in high CO₂ determine the appearance of BH and increase the rate of AA loss, probably through a reduction in the turnover of antioxidants. © 2002 Society of Chemical Industry     

Sex differences in social reinstatement motivation of the domestic chick (Gallus gallus) revealed by runway tests with social and nonsocial reinforcement.

Male and female chicks (Gallus gallus) were trained at 4 days old to run along a corridor to reach a goal box that contained either cagemates (social reinforcement) or food (nonsocial reinforcement). Females ran faster when social reinforcement was used, whereas males ran faster with nonsocial reinforcement. When social reinforcement was used with a V-shaped runway, in which chicks had to proceed toward the goal object in an indirect fashion, sex differences were reversed. The results may be due to stronger social reinstatement tendencies in females than in males: Higher levels of social motivation facilitate behavioral performance when the task is easy (straight runway) and inhibit it when the task is difficult (V-shaped runway). (PsycINFO Database Record (c) 2010 APA, all rights reserved)