Effective forces in square well and square shoulder fluids

We derive an analytical expression for the effective force between a pair of macrospheres immersed in a sea of microspheres, in the case where the interaction between the two unlike species is assumed to be a square well or a square shoulder of given range and depth (or height). This formula extends a similar one developed in the case of hard core interactions only. Qualitative features of such effective force and the resulting phase diagram are then analyzed in the limit of no interaction between the small particles. Approximate force profiles are then obtained by means of integral equation theories (PY and HNC) combined with the superposition approximation and compared with exact ones from direct Monte Carlo simulations.Comment: 34 page

A sonographic spectrum of psoriatic arthritis: “the five targets”

Ultrasound is a rapidly evolving technique that is gaining an increasing success in the assessment of psoriatic arthritis. Most of the studies have been aimed at investigating its ability in the assessment of joints, tendons, and entheses in psoriatic arthritis patients. Less attention has been paid to demonstrate the potential of ultrasound in the evaluation of skin and nail. The aim of this pictorial essay was to show the main high-frequency grayscale and power Doppler ultrasound findings in patients with psoriatic arthritis at joint, tendon, enthesis, skin, and nail level

INTERFEROMETRIC INVESTIGATIONS OF CONVECTION AROUND CYLINDERS AT SMALL GRASHOF NUMBERS

Experiments with a Twyman-Green interferometer have been carried out to determine the temperature distribution around a horizontal cylinder in the presence of natural convection for Grashof numbers around 10-4 and a Prandtl number of 0.7, a region of parameters poorly covered by previous investigations. Temperature differences are recovered by digital analysis of the fringe pattern perturbation. The results indicate significant discrepancies in the temperature profile, when compared with numerical models

AUTOMATIC FRINGE RECOGNITION AND DETECTION OF SUBWAVELENGTH PHASE PERTURBATIONS WITH A MICHELSON INTERFEROMETER

Simple systems and procedures based on personal computer hardware to analyze the fringe pattern in a Michelson interferometer, retrieve information on the irregularities of the combined phase front and use it to obtain a correct interferogram are presented. In one system, where one of the mirrors can be moved piezoelectrically, good sensitivity (λ/30) is obtained while using an economical array of 1-bit image sensing elements. In another system, based on a TV camera and a 6-bit frame grabber, images of the two separate laser beams and of the fringe patterns are stored; by adequate numerical analysis, higher sensitivity (λ/100) is achieved

A 1-D model of the formation and evolution of Polar Stratospheric Clouds

A 1-D model of the formation and seasonal evolution of Polar Stratospheric Clouds (PSCs) is described. The model considers PSCs of types 1 and 2 in the vertical range from 8 to 30 km and utilizes real temperature data. The micro-physical processes included in the model are the heterogeneous nucleation and condensation (or evaporation), while sedimentation, gas diffusion and vertical wind velocity are the processes responsible for transport. Model simulations have been compared with PSC data obtained by lidar at the South Pole: results for the winter 1990 are discussed. The different contribution of type 1 and type 2 PSCs to the measured backscattering coefficient has been evidenced. In the simulations, layers of NAT particles form when low values of the backscattering coefficient are measured; similarly, ice particles form when sharper and rapidly changeable structures with higher values of the backscattering coefficient are observed. Significant results on the condensation and depletion of HNO3 and H2O are presented. Water vapor profiles measured during winter 1990 are reproduced quite well

Attivazione e primi risultati dell’interferometro geodetico nel Laboratorio Nazionale del Gran Sasso

An underground laser strainmeter, crossing a fault in the Gran Sasso massif, is discontinuously operating since late May 1994, after a few years of mechanical stabilization of end monuments. Its main characteristics are: high sensitivity (Δl/l ≈ 3 × 10−12), large dynamic range (up to 10−4), fast sampling rate (2 kHz), and the capability of following strain rates as sharp as 7 × 10−5 s−1. A swift extensional strain transient reaching a peak of at least 1 microstrain occurred in about one month from the beginning of the operating time, followed by a four-month-long coarsely stable period, and a slower decay. On June 2nd 1994, in coincidence with two local earthquakes, permanent extensional offsets of about 10 ne have been recorded. A further aseismic slip of the same order of magnitude and sign has been observed about thirty minutes arter the last preceding local event, and ten minutes before the next following one. At the same time, the arrival of seismic waves from a distant earthquake has been recorded by the interferometer. No similar signal behaviour has been observed any more since then