CASCADE REFRIGERATION SYSTEM FOR LOW TEMPERATURES USING NATURAL FLUIDS

Cascade refrigeration systems work with two or more serial disposed cycles and can obtain internal temperatures below -60°C, which is necessary for several activities in medicine and scientific research. This paper presents a thermodynamic analysis of cascade system refrigeration using natural refrigerant fluids for ultra-low temperatures. These fluids are environmentally friendly refrigerant and are an alternative to hydro chlorofluorocarbons (HCFCs) and to hydrofluorocarbons (HFCs). Energy and exergy analyses were performed using a thermodynamic model based on the law of conservation of mass and also on the first and second laws of thermodynamics. A simulator was developed to assess the technical practicability of this system, considering it running as a real refrigeration cycle. Natural fluids have best performance energetically and environmentally

Truncated states obtained by iteration

Quantum states of the electromagnetic field are of considerable importance, finding potential application in various areas of physics, as diverse as solid state physics, quantum communication and cosmology. In this paper we introduce the concept of truncated states obtained via iterative processes (TSI) and study its statistical features, making an analogy with dynamical systems theory (DST). As a specific example, we have studied TSI for the doubling and the logistic functions, which are standard functions in studying chaos. TSI for both the doubling and logistic functions exhibit certain similar patterns when their statistical features are compared from the point of view of DST. A general method to engineer TSI in the running-wave domain is employed, which includes the errors due to the nonidealities of detectors and photocounts.Comment: 10 pages, 22 figure

Simulation of the interband s–d and intraband s–s electron–phonon contributions to the temperature dependence of the electrical resistivity in Fe/Cr multilayers

High-resolution electrical resistivity (rho, d rho/dT) measurements were performed in three series of [Fe-30 Cr-Angstrom(t) (Angstrom)] multilayers in the temperature range 15-300 K, with an applied magnetic saturation field (7.5 kOe). The samples were deposited by molecular beam epitaxy on MgO substrates and by sputtering on MgO and Si substrates. For T 150 K the resistivity attains the classical regime with rho proportional to T. To simulate the observed rho(i)(T) we have used a model that takes into account intraband s-s and interband s-d electron-phonon scattering, written as rho(sd) = A X f(1)(T) and rho(ss) = B X f(2)(T), where f(1) and f(2) are functions only of the temperature, A and B are sample-dependent constants and rho(i) = rho(sd) + rho(ss). The model predicts that rho(i) proportional to T-3 at low temperatures and rho(i) proportional to T at high temperatures as observed in our multilayers. The experimental curves of rho(i) and d rho/dT are well reproduced in the whole temperature range (15-300 K) and from the fits to these curves A and B are determined for each sample. By plotting B vs A we find that each point from all the multilayers falls in a straight line indicating that B is proportional to A. The simulated resistivity thus predicts that rho(i) = beta f(T) where f(T) = alpha(1) x f(1)(T) + alpha(2) x f(2)(T) is a function only of the temperature, as observed experimentally

Church-Rosser Systems, Codes with Bounded Synchronization Delay and Local Rees Extensions

What is the common link, if there is any, between Church-Rosser systems, prefix codes with bounded synchronization delay, and local Rees extensions? The first obvious answer is that each of these notions relates to topics of interest for WORDS: Church-Rosser systems are certain rewriting systems over words, codes are given by sets of words which form a basis of a free submonoid in the free monoid of all words (over a given alphabet) and local Rees extensions provide structural insight into regular languages over words. So, it seems to be a legitimate title for an extended abstract presented at the conference WORDS 2017. However, this work is more ambitious, it outlines some less obvious but much more interesting link between these topics. This link is based on a structure theory of finite monoids with varieties of groups and the concept of local divisors playing a prominent role. Parts of this work appeared in a similar form in conference proceedings where proofs and further material can be found.Comment: Extended abstract of an invited talk given at WORDS 201