117,506 research outputs found
Spectroscopic and theoretical approaches for studying radical reactions in class I ribonucleotide reductase
No full textRibonucleotide reductases (RNRs) catalyze the production of deoxyribonucleotides, which are essential for DNA synthesis and repair in all organisms. The three currently known classes of RNRs are postulated to utilize a similar mechanism for ribonucleotide reduction via a transient thiyl radical, but they differ in the way this radical is generated. Class I RNR, found in all eukaryotic organisms and in some eubacteria and viruses, employs a diferric iron center and a stable tyrosyl radical in a second protein subunit, R2, to drive thiyl radical generation near the substrate binding site in subunit R1. From extensive experimental and theoretical research during the last decades, a general mechanistic model for class I RNR has emerged, showing three major mechanistic steps: generation of the tyrosyl radical by the diiron center in subunit R2, radical transfer to generate the proposed thiyl radical near the substrate bound in subunit R1, and finally catalytic reduction of the bound ribonucleotide. Amino acid- or substrate-derived radicals are involved in all three major reactions. This article summarizes the present mechanistic picture of class I RNR and highlights experimental and theoretical approaches that have contributed to our current understanding of this important class of radical enzymes
Restituire parole. Una ricerca autobiografica a Lampedusa
No full textIl volume è l'esito di una ricerca autobiografica triennale a Lampedusa effettuata con la comunità lampedusana e con i giovani dell'Istituto comprensivo L. Pirandello di Lampedus
A cohesive-zone model for steel beams strengthened with pre-stressed laminates
No full textAbstractWe analyse the problem of a simply supported steel beam subjected to uniformly distributed load, strengthened with a pre-stressed fibre-reinforced polymer (FRP) laminate. According to the assumed application technology, the laminate is first put into tension, then bonded to the beam lower surface, and finally fixed at both its ends by suitable connections. The beam and laminate are modelled according to classical beam theory. The adhesive is modelled as a cohesive interface with a piecewise linear constitutive law defined over three intervals (elastic response, softening response, debonding). The model is described by a set of differential equations with suitable boundary conditions. An analytical solution to the problem is determined, including explicit expressions for the internal forces and interfacial stresses. For illustration, an IPE 600 steel beam strengthened with a Sika® Carbodur® FRP laminate is considered. First, the elastic limit state load of the unstrengthened beam is determined. Then, the loads corresponding to the elastic limit states in the steel beam, adhesive, and laminate for the strengthened beam are calculated. As a result, the increased elastic limit state load of the strengthened beam is obtained
A distributed amplifier system for bilayer lipid membrane (BLM) arrays with noise and individual offset cancellation
No full textLipid bilayer membrane (BLM) arrays are required for high throughput analysis, for example drug screening or advanced DNA sequencing. Complex microfluidic devices are being developed but these are restricted in terms of array size and structure or have integrated electronic sensing with limited noise performance. We present a compact and scalable multichannel electrophysiology platform based on a hybrid approach that combines integrated state-of-the-art microelectronics with low-cost disposable fluidics providing a platform for high-quality parallel single ion channel recording. Specifically, we have developed a new integrated circuit amplifier based on a novel noise cancellation scheme that eliminates flicker noise derived from devices under test and amplifiers. The system is demonstrated through the simultaneous recording of ion channel activity from eight bilayer membranes. The platform is scalable and could be extended to much larger array sizes, limited only by electronic data decimation and communication capabilities
Effetto della tecnica di allevamento sul comportamento antipredatorio della starna (Perdix perdix L.).
No full textEffetto della temperatura ambientale sul consumo giornaliero di mangime e sul CUDa nelle lepri
No full textSince the effect of environmental temperature on food utilisation in hares is not well known, we studied the relationship between temperature, hare daily feed intake and digestibility. Ten couple bred hares, ad libitum fed with a commercial pellet (crude protein 17% and crude fibre 21%) were monitored from April to June in Tuscany. The recorded temperature in this period changed from 8°C to 25°C. Results showwd that the highest temperatures reduce the daily intake and the apparent digestibility
Dynamic Behaviour of a Medieval Masonry Bell Tower. Part 2: Measurement and Modelling of the Tower Motion
No full textThe work described herein was conducted within the framework of an ongoing research program on the dynamic behavior of the Tower of Matilde, the bell tower of the Cathedral of San Miniato, Pisa, Italy, an interesting case study for its current structural arrangement and the modifications it has undergone over the centuries. This is Part 2 of a more extensive publication dealing with the results of such research and presents the experimental measurements and analyses conducted in order to determine the motion of the tower subjected to the actions produced by the motion of the two largest of its six bells. The numerical and analytical models adopted to interpret the experimental results, from the most elaborate and complex to the simplest ones, have all confirmed that the third harmonic frequency of oscillation of the largest bell is very close to the first eigenfrequency of the bell tower structure. Such studies moreover have enabled making a first approximation of the values of the global mechanical parameters characterizing the tower’s dynamic behavior
Reducing Leakage through Filter Cache
No full textWe evaluate the leakage reduction for both instruction and data cache in presence of drowsy or decay techniques. We discovered that a filter cache, traditionally used for reducing active power, can help reduce also leakage. The key idea is to reduce the lifetime of the lines that are in high-power state inside a leakage-saving cache. Power consumption has become one of the main concerns for designers, together with the performance. Caches account for the largest fraction of on-chip transistors in most modern processors. Therefore, they are a primary candidate for attacking the problem of the leakage. In average, for instruction cache 24\% improvement in leakage savings and 1.5\% in IPC (Instruction Per Cycle) can be achieved with respect to drowsy cache. For data caches, 5\% and 5.4\% improvement can be achieved respectively. Experiments have been performed also with decay cache showing fewer benefits
Dynamic Behaviour of a Medieval Masonry Bell Tower. Part 1: Bell Dynamic Action Measurement and Modelling
No full textThe work described herein was conducted within the framework of an ongoing research program on the dynamic behavior of the Tower of Matilde, the bell tower of the Cathedral of San Miniato, Pisa, Italy, an interesting case study for its current structural arrangement and the modifications it has undergone over the centuries. This paper (Part I) details the experimental analyses performed in order to obtain an accurate measure of both the motion of the tower's bells and, consequently, the time function of the dynamic actions transmitted to the tower during their motion. We then demonstrate how it is possible to arrive at an accurate, even though approximate, analytical description of both the bells' motion and their actions by means of only a few experimental measurements and a simple mechanical model (also called in the following additional mass model)
Heterogeneous nucleation and heat flux avalanches in La(Fe, Si)13 magnetocaloric compounds near the critical point
No full textThe phase transformation kinetics of LaFe11.41Mn0.30Si1.29-H1.65 magnetocaloric compound is addressed by low rate calorimetry experiments. Scans at 1 mK/s show that its first order phase transitions are made by multiple heat flux avalanches. Getting very close to the critical point, when the transition becomes of the second order type, the step-like discontinuous behaviour associated with avalanches is smoothed out and the thermal hysteresis disappears. This result is confirmed by magneto-resistivity measurements and allows to obtain accurate values of the temperature hysteresis (DThyst = 0.37 K) at zero external magnetic field and of the critical field (Hc = 1.19 T). The number and magnitude of heat flux avalanches change as the magnetic field strength is increased, showing the interplay between the intrinsic energy barrier between phases and the microstructural disorder of the sample
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