Efficient computation of hashes

The sequential computation of hashes at the core of many distributed storage systems and found, for example, in grid services can hinder efficiency in service quality and even pose security challenges that can only be addressed by the use of parallel hash tree modes. The main contributions of this paper are, first, the identification of several efficiency and security challenges posed by the use of sequential hash computation based on the Merkle-Damgard engine. In addition, alternatives for the parallel computation of hash trees are discussed, and a prototype for a new parallel implementation of the Keccak function, the SHA-3 winner, is introduced

A laser diode based system for calibration of fast time-of-flight detectors

A system based on commercially available items, such as a laser diode, emitting in the visible range $\sim 400$ nm,and multimode fiber patches, fused fiber splitters and optical switches may be assembled,for time calibration of multi-channels time-of-flight (TOF) detectors with photomultipliers' (PMTs') readout. As available laser diode sources have unfortunately limited peak power, the main experimental problem is the tight light power budget of such a system. In addition, while the technology for fused fiber splitters is common in the Telecom wavelength range ($\lambda \sim 850, 1300-1500$ nm), it is not easily available in the visible one. Therefore, extensive laboratory tests had to be done on purpose, to qualify the used optical components, and a full scale timing calibration prototype was built. Obtained results show that with such a system, a calibration resolution ($\sigma$) in the range 20-30 ps may be within reach. Therefore, fast multi-channels TOF detectors, with timing resolutions in the range 50-100 ps, may be easily calibrated in time. Results on tested optical components may be of interest also for time calibration of different light detection systems based on PMTs, as the ones used for detection of the vacuum ultraviolet scintillation light emitted by ionizing particles in large LAr TPCs.Comment: submitted to JINS

Behaviour in Magnetic Fields of Fast Conventional and Fine-Mesh Photomultipliers

The performance of both conventional and fine-mesh Hamamatsu photomultipliers has been measured inside moderate magnetic fields. This has allowed the test of effective shielding solutions for photomultipliers, to be used in time-of-flight detectors based on scintillation counters. Both signal amplitude reduction or deterioration of the timing properties inside magnetic fields have been investigated

The interpretation of the solutions of the Wheeler De Witt equation

We extract transition amplitudes among matter constituents of the universe from the solutions of the Wheeler De Witt equation. The physical interpretation of these solutions is then reached by an analysis of the properties of the transition amplitudes. The interpretation so obtained is based on the current carried by these solutions and confirms ideas put forward by Vilenkin.Comment: 11 pages, latex, no figure

Plasma cortisol variations in dairy cows after some usual or unusual manipulations

The increase of blood cortisol is a common consequence of the acute stress; this has generally positive effects, despite not completely understood (Sapolsky et al. 2000). However, at least in human beings under chronic stress, the hypothalamic-pituitary-adrenal system – responsible of cortisol release – is deregulated, resulting in pathophysiological changes, which may develop into various types of disorders (Tafet and Bernardini, 2003)

Adrenal responsiveness to a low-dose ACTH challenge in early and late lactating dairy cows.

To improve the evaluation of the chronic stress conditions, the adrenal responsiveness to low dose ACTH stimulation, in different lactation stages, was checked in 56 multiparous dairy cows from 2 herds (25-350 days in milk). Cows were retrospectively ranked in 3 stages: early (150 DIM) lactation. Herd B (vs. herd A) showed higher basal cortisol and frequency of inflammation. Early stage (vs. others) showed higher basal cortisol, bilirubin, ceruloplasmin and haptoglobin, as well as lower ones of cholesterol and lower rise of plasma cortisol during ACTH challenge (P<0.001). Cortisol peak was also correlated negatively with ceruloplasmin, bilirubin, ROM, and positively with cholesterol, vitamin A and E. Both, basal cortisol and cortisol response to ACTH, are associated to inflammation but in opposite way: basal cortisol positively and cortisol response negatively. This latter results are likely due to lower transcortin synthesis, that could be ensued in early lactating cows suffering inflammation

Change of digesta passage rate in dairy cows after different acute stress situations

Six dairy cows received 3 treatments after morning meal, in a double Latin square design. Treatments were ACTH challenge (SYN), hoof trimming (TRIM) and saline (CTR). Measurements included: plasma cortisol and metabolic profile during the 24 h after treatments; the rate of digesta passage, faecal dry matter and pH. Both acute stress situations vs CTR caused a rapid and similar rise in plasma cortisol (P<0.001), while plasma glucose increased only in response to TRIM. Plasma concentrations of urea and BHB were increased for several hours after both stress situations. Most importantly, the transit time of digesta was reduced with SYN and TRIM (P<0.05). Our data demonstrate a reduced forestomach motility during acute stress and confirm a possible negative linkage between stress and gut functions, perhaps independent of diet composition. The mechanism seems linked to increased ACTH or cortisol rather than corticotrophin-releasing factor

Hysteresis and spin phase transitions in quantum wires in the integer quantum Hall regime

We demonstrate that a split-gate quantum wire in the integer quantum Hall regime can exhibit electronic transport hysteresis for up- and down-sweeps of a magnetic field. This behavior is shown to be due to phase spin transitions between two different ground states with and without spatial spin polarization in the vicinity of the wire boundary. The observed effect has a many-body origin arising from an interplay between a confining potential, Coulomb interactions and the exchange interaction. We also demonstrate and explain why the hysteretic behavior is absent for steep and smooth confining potentials and is present only for a limited range of intermediate confinement slopes.Comment: submitted to PR