Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Whole body vibration in mountain-rescue operations

In mountain-rescue operations injured people are generally exposed to vibrations and shocks that can be potential causes of physical conditions worsening. Such vibrations can derive both from patient's body manipulations (e.g. when it is being loaded and immobilized on a stretcher) and from forces coming from the transport devices and vehicles. Despite the general feeling that during this kind of operations the levels of transmitted vibrations to the injured can be quite large and potentially dangerous, there is practically no study in literature providing reliable parameters (i.e. measurements) to support or dismiss these beliefs. This paper reports the results of a measurement campaign carried-out in order to outline, identify and quantify the excitations a human body is exposed to, during typical transportation phases related to mountain-rescue operations. The work mainly presents and discusses the experimental setup with the aim of focusing on the problems related to this kind of measurements; the results of the experimental campaign carried-out for the measurement of the vibrations undergone by a human body during a simulated rescue operation are presented and discussed as well. Such simulation includes three phases of transportation: on a hand-held stretcher, on an ambulance and on a helicopter. The work is not intended to supply a complete characterization and analysis of vibrations transmission during any rescue operation but just to provide a preliminary overview and to define a measurement method that can be applied for a more comprehensive characterization. With such aims measurements were carried out in on-field situations stated as “typical” by rescue experts and data then analyzed both with standard procedures and algorithms (e.g. ISO 2631s weighting curves) and with the commonly used statistical indexes; in the analysis it is important to be aware that standardized measurement procedures and indexes, created to verify comfort or health-risks of workers, might not fit the case of a generic patient who experienced a serious mountain accident. The work includes also a laboratory activity mainly related to mechanical characterization of the stretcher used in the field tests. The most interesting result of the study is the comparison of the vibration levels in the various rescue phases that, even when using different indicators, shows that the most critical issue is due to hand transportation despite the bad judgment usually expressed for helicopter flight.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Surface tension in Ising systems with Kac potentials

We consider an Ising spin system with Kac potentials in a torus of ^d,d>-2, and fix the temperature below its Lebowitz-Penrose critical value. We prove that when the Kac scaling parameter vanishes, the log of the probability of an interface becomes proportional to its area and the surface tension, related to the proportionality constant, converges to the van der Waals surface tension. The results are based on the analysis of the rate functionals for Gibbsian large deviations and on the proof that they -converge to the perimeter functional of geometric measure theory (which extends the notion of area). Our considerations include nonsmooth interfaces, proving that the Gibbsian probability of an interface depends only on its area and not on its regularity.     

The formation of highly fluorescent zinc phosphate in the presence of uranium and its application to the direct fluorimetry of uranium in aqueous media

The formation and composition of highly fluorescent zinc phosphates in the presence of traces of uranium were investigated and a direct fluorimetric determination of uranium in aqueous media was developed, based on the formation of finely dispersed and stabilized fluorescent precipitates. The standard deviation for 20 μg of uranium, in 25 ml is 5% ; with the fluorimeter described, 10^-2 μg of uranium per ml can be determined with an error of 50%. The method is very selective and can be employed for analysis of uranium in ores; it is less sensitive than conventional fluorimetry of fused alkali fluorides but is much simpler and faster. Interferences can often be eliminated by suitable masking reactions.     

Stochastic linear maps and transition probability

Some aspects of the transition probability P(, ) between states , on unital ^*-algebras are discussed. It is shown that P increases under the action of any stochastic linear map T, i.e., P(T, T)P(, ). Some properties of P are derived in starting from a recently-proved characterization of the quantity in question.