Comments on ?Probability Distributions for the Number of Radio Transceivers which can Communicate with One Another?

We discuss the correctness of one of the main results of [1] about the probability density function of the distance between two audible nodes in an infinite 2-dimensional scenario. We prove that result [1, eq. (7)] is wrong and derive a more general expression, which is valid for an infinite d?dimensional area. It is worth noting that, although the results on the distribution of the distance between two nodes are wrong, the other results of [1], and in particular the fact that the number of audible nodes in an arbitrary area is a Poisson r.v. is correct.     

Pseudoangiomatous hyperplasia of the mammary stroma: true entity or phenotype?

We report the clinical and pathologic features seen in 14 cases of pseudoangiomatous hyperplasia of the mammary stroma. The lesion manifested as a discrete palpable lump in twelve women and two men. The excisional biopsy specimens showed firm, circumscribed grey-tan lesions measuring from 3 to 5.5 cm in largest dimension. Histologic study revealed diffuse, anastomosing, enlongated slits with open lumina, covered by spindle cells with bland nuclei and no mitotic activity. Strong reactivity for vimentin and CD34 was noted. Smooth muscle actin was focally noted in most cases. Immunostains for other markers, including CD31 and factor VIII related antigen was negative. Spindle cells from two cases expressed both estrogen and progesterone receptors. In all the cases, there was some degree of glandular hyperplasia accompanying the stromal changes. Fibroadenoma or fibrocystic disease were also common features. Our study confirms that pseudoangiomatous hyperplasia of mammary stroma represents a proliferation of local myofibroblasts, likely related to a hormonal stimulus. The wide range of associated changes of breast parenchyma further indicates that this lesion may represent a local, non specific change rather than a true clinico-pathologic entity.     

Interference Analysis in a Poisson Field of Nodes of Finite Area

The research for analytical models that are able to estimate the amount of interference, which is the most important cause of performance degradation in wireless networks, has received a lot of attention over the past few years. This interest is expected to increase in the next few years due to the advent of new architectures and communication technologies, such as wireless networks sharing the same (unlicensed) frequency band, infrastructureless wireless networks, and ultrawideband (UWB) systems. In this paper, we try to overcome some of the limitations of the existing interference models and propose an analytical framework for the evaluation of any statistical moment of the interference provided by a Poisson field of nodes located on a given region of limited area. The propagation environment we consider is characterized by a deterministic distance-dependent path-loss model and log-normal shadowing. The present methodology can be used to provide a fast and accurate evaluation of the amount of interference in many practical situations. Exact closed-form expressions are given for some specific cases.     

Analysis of the impact of process variations on clock skew

In this paper, we analyze the impact of process variations on the clock skew of VLSI circuits designed in deep submicrometer technologies. With smaller feature size, the utilization of a dense buffering scheme has been proposed in order to realize efficient and noise-immune clock distribution networks. However, the local variance of MOSFET electrical parameters, such as V_T and I_DSS, increases with scaling of device dimensions, thus causing large intradie variability of the timing properties of clock buffers. As a consequence, we expect process variations to be a significant source of clock skew in deep submicrometer technologies. In order to accurately verify this hypothesis, we applied advanced statistical simulation techniques and accurate mismatch measurement data in order to thoroughly characterize the impact of intradie variations on industrial clock distribution networks. The comparison with Monte Carlo simulations performed by neglecting the effect of mismatch confirmed that local device variations play a crucial role in the design and sizing of the clock distribution network     

Sulle regioni di confidenza per i parametri dei modelli non lineari. I

Sommario Nell'ambito della ricerca sperimentale si presenta il problema di stimare i parametri di un modello interpretativo teorico che ne dipende in modo non lineare. In concreto però, come per il caso lineare, le stime puntuali, ottenute tipicamente secondo il principio dei minimi quadrati, possono avere, in sè, scarso rilievo per la variabilità ad esse inerente a causa dell'errore sperimentale e vengono impiegate per la determinazione di insiemi di valori che hanno una prefissata probabilità di comprendere quelli degli incogniti parametri in studio (regioni di confidenza). Nel presente studio si propone un miglioramento, in modo da tener conto della ?curvatura?, del metodo di uso corrente, che fa ricorso alla ?linearizzazione locale? del modello per ottenere regioni di confidenza approssimate. La teoria qui proposta si basa: 1) sull'interpretazione di un modello non lineare ink (k>1) parametri come una varietà riemannianaV _(k) immersa in uno spazio euclideoS _(n) di dimensioni pari al numeron(n>k+1) delle osservazioni; 2) sulla sua identificazione con unaipersuperficie, che sotto particolari condizioni, meglio approssimaV _(k) , per quanto riguarda la curvatura globale media, nell'intorno del punto corrispondente alle stime dei parametri. Si propongono due tipi di regioni di confidenza, uno generale ed uno sotto l'ipotesi che laipersuperficie approssimante sia convessa. La teoria proposta si lascia agevolmente formalizzare in una procedura di calcolo automatico di cui si indicano gli elementi costitutivi e si illustra l'applicazione ad un modello di cinetica chimica.

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Abtract In the experimental research we are often confronted with theoreitcal models which are non-linear in the parameter. As in the linear case, point estimates of the latter, typically obtained by the method of least squares, can result of little interest by themselves, because of the random variability inherent to them and they are rather taken as a basis for constructing sets with assigned probability of containing the ?true? unknown values of the parameters (confidence regions). In the former context an improvement of the current procedure, by which confidence regions are determined through ?local linearization? of the response functions, is proposed, in order to take the ?curvature? of the model into consideration. The theory developed in this paper is based: 1) on the identification of a non-linear model ink (k>1) parameters with a Riemann space imbedded in an euclideann dimensional spaceS _(n) , withn (n>k+1) equal to the number of observations; 2) on an approximation ofV _(k) by asurface of aS _(k+1), which is the best, in a particular class, insofar, as its ?mean curvature? is the nearest to that ofV _(k) in the point corresponding to the least squares estimates of the parameters. Two types of confidence regions are then obtained: the one more general, the other under the hypothesis that the approximatingsurface is convex. The former theoretical results can be easily formalized into a computer programme, the leading elements of which are presented in the paper together with an application of it to a model arising in the study of a chemical mechanism.

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Uno stralcio dell'artioolo è stato presentato come comunicazione alla Sessione Metodologica dello VIII Convegno Nazionale dell'Associazione Italiana per il Controllo della Qualità (Napoli 10-11-5-1973).     

Contention-TDMA protocol: performance evaluation

A hybrid access protocol known, as contention time-division multiple access (C-TDMA), is presented and analyzed in a radio cellular multiuser system scenario. C-TDMA shows some features of contention-based (slotted-ALOHA) and reservation-based (packet reservation multiple access, PRMA) protocols. It has been recommended for use in the uplink of future European multimedia distribution systems. A simple Markov model is proposed to describe C-TDMA behavior. A complete statistical analysis of the model has been made in order to evaluate the performance of the protocol. However, due to the long computation time required in the presence of a large number of users, a simpler approach known as equilibrium point analysis (EPA) is used. Moreover, on the basis of the EPA analysis and the C-TDMA design parameters, a fast algorithm has been developed to improve the achievable throughput of C-TDMA. Results in terms of throughput and delay under variable traffic conditions indicate that C-TDMA is able to grant optimum throughput/delay figures for typical multiuser systems. Moreover, for a digital speech scenario, a performance comparison with PRMA demonstrates that C-TDMA yields equivalent performance to PRMA in terms of number of users supported by the system with a limited packet dropping rate     

On the use of wireless networks at low level of factory automation systems

Wireless communication systems are rapidly becoming a viable solution for employment at the lowest level of factory automation systems, usually referred to as either "device" or "field" level, where the requested performance may be rather critical in terms of both transmission time and reliability. In this paper, we deal with the use of wireless networks at the device level. Specifically, after an analysis of the communication requirements, we introduce a general profile of a wireless fieldbus. Both the physical and data link layers are taken directly from existing wireless local area networks and wireless personal area networks standards, whereas the application layer is derived from the most popular wired fieldbuses. We discuss implementation issues related to two models of application layer protocols and present performance results obtained through numerical simulations. We also address some important aspects related to data security and power consumption.     

CO2/O2 anesthesia for the castration of male piglets (preliminary results)

Introduction of anaesthesia with CO2/O2 (60% to 40%) is possible within 90 and 120 seconds. There are moderate to excessive excitations occurring as part of state II of anaesthesia. Anaesthesia (during castration) in CO2/O2-atmosphere produces excellent analgesia and relaxation. The duration of castration surgery is much shorter under CO2-anaesthesia than without anaesthesia. Blood cortisol levels are significantly higher after castration without CO2-anaesthesia. About 5 minutes after CO2/O2-anaesthesia and castration surgery, piglets are already awake and standing.