IR emission from circumstellar envelopes of C-rich stars

The reliability of a theoretical model that solves the radiative transfer equation in dust clouds surrounding a central star is checked. In particular, it is found that both classical scattering by dust and the back-heating effects are negligible in the radiative transfer when envelopes similar to IRC+10216 are taken into consideration. In addition, new fits of IRC+10216 spectra are presented which were obtained, when the source is in different luminosity phases, under the assumption that amorphous carbon grains are in the circumstellar envelope. The same model is currently used to simulate the emission from carbon-rich sources showing the silicon carbide feature at 11.3 microns

Experimental evidence for amorphous carbon grains in comets

Amorphous carbon grains similar to those produced in the laboratory, but with a higher hydrogen content, appear to be good candidates to simulate both the IR continuum emission and the 3.4 micron band measured for P/Halley. The comparison of the cometary features with those detected in the laboratory for carbon grains characterized by various sp(exp 2)/sp(exp 3) ratios seems to indicate that a prevalent diamond-like (sp(exp 3)) structure should be present in cometary particles. These kinds of solid particles seem also suitable to explain the daily and monthly variations of the 3.4 micron band intensity, relative to the continuum, and, at the same time,- to fulfill the abundance constraints. The same grains appear to be able to reproduce the absorption bands detected in the IR galactic source IRS 7. This result may be considered as a first experimental evidence of a relation existing between interstellar dust and cometary materials

Raman properties of various carbonaceous materials and their astrophysical implications

It is well known that a large number of celestial objects exhibit, in the range 3 to 12 micron, a family of emission features called unidentified infrared bands (UIR). They usually appear together and are associated with UV sources. Recently various authors have suggested that these features could be attributed to solid carbonaceous materials. Following this interest, a systematic analysis was performed of various types of amorphous carbon grains and polycyclic aromatic hydrocarbons (PAH), produced in lab. Updating results of Raman measurements performed on several carbonaceous materials, chosen according to their astrophysical interest, are presented. The measurements were made by means of a Jobin-Yvon monochromator HG2S and standard DC electronic. The line at 5145 A of an Ar+ laser was used as excitation source

On the Simultaneous Conjugate Match of N-Port Networks

Some advancements are proposed to the theory of simultaneous conjugate match (SCM) of N -ports. It is shown that, if a network qualifies for geometrical unconditional stability (g-), then it can be matched simultaneously at all ports. The proof serves as the basis for constructing an iterative algorithm (AlgG) which is guaranteed to converge to the SCM condition for all N -ports exhibiting g-. In addition to the main results above mentioned, two more iterative algorithms are presented (AlgS and AlsA), which are conjectured to work for all networks satisfying g-. AlgS can be shown to converge globally for TEXPRESERVE3 and AlgA to converge locally for all N . Besides their theoretical interest, these results find a natural application in the matching of passive networks, and in particular of N -element phased arrays. However, they can be applied to any (i.e., also active) N -port as long as this is known to exhibit g-

Partitioned Ohtomo stability test for efficient analysis of large-signal solutions

A fundamental step in the design of electronic circuits is the verification that they are stable at least on a given set of external terminations, in order to avoid that the solution found be not observable in practice. This is especially true at microwave and millimeter-wave circuits, which are typically analyzed in the frequency domain rather than in the time domain. As a consequence, both in the linear and large-signal case, unstable solutions may be found instead of an observable one. Unfortunately, as compared to the linear case, the stability analysis of large-signal solutions is significantly more cumbersome. In particular, although it is possible to translate the small-signal tests based on the Nyquist principle to large-signal equivalents, the price to pay is a significant increase in matrix size. In the case of the Ohtomo test, which has only recently been applied to large-signal solutions, it is however possible to exploit the structure of the problem to significantly reduce the complexity and, therefore, simulation time. A real-world balanced amplifier is selected to validate the proposed method and illustrate its practical usage. The application of the method to a realistic monolithic circuit with a large number of devices is also presented

Cost-effectiveness analysis of initial HIV treatment under Italian guidelines

INTRODUCTION: Since the mid-1990s, highly active antiretroviral therapy (HAART) has modified the clinical course of human immunodeficiency virus (HIV) infection, reducing the rate of disease progression, the incidence of opportunistic infections, and mortality. The authors of this paper performed an economic analysis to estimate the cost-effectiveness of the HAART regimens in Italy for managing HIV-infected patients according to national guidelines. PATIENTS AND METHODS: The incremental cost-effectiveness analysis was carried out by means of a Markov model, which through a decision-analytic approach, made it possible to compare the studied antiretroviral regimens. The population considered in the model consisted of adult subjects with HIV who received antiretroviral HAART treatment for the first time. The population considered in the analysis reflects the patients' characteristics according to one of the regional surveillance systems HIV/AIDS infection report currently operating in Italy. The analysis was carried out from the point of view of the Italian health care system. The considered outcome measures were quality-adjusted life years (QALYs) and direct health costs calculated for the year 2010. Both the outcomes (QALYs) and the costs were discounted by 3.5%. The time horizon adopted in the model was 10 years. RESULTS: The model shows, in terms of cost per gained QALY, single tablet regimen (STR) appeared to be the most cost-effective therapeutic choice (22,017), followed by tenofovir (TDF) + lamivudine + efavirenz (EFV) (24,526), and TDF/emtricitabine (FTC) + nevirapine (26,416), and TDF + FTC + EFV (26,558); the remaining strategies have an incremental cost-effectiveness ratio (ICER) value varying from 28,000 to 41,000 per QALY. The sensitivity analysis on the main variables confirmed the validity of the base case scenario. CONCLUSION: STR is the most cost-effective treatment strategy, compared with the other therapeutic regimens recommended by the Italian guidelines. All the ICER values of the various regimens considered by the Italian guidelines were lower than the threshold value of 50,000 commonly accepted at the international level. The model developed represents a tool for policy makers and health care professionals to make short- and long-term cost projections and thus evaluate their impact on the available budgets for HIV patients

VUV-visible measurements on different samples of amorphous carbon

Among various candidate materials for interstellar dust, amorphous carbon (AC) is playing an increasingly important role (Greenstein, 1981; Hecht et al., 1984; Jura, 1983, 1986). Furthermore, recent in situ measurements have clearly shown the presence of carbonaceous grains in the coma of comet Halley (Kissel et al., 1986). Laboratory investigations on AC grains may be very useful to better interpret observations and to support theoretical elaborations. Recently, the authors started an international research program which also includes UV extinction analyses on AC samples, by using synchrotron light. Preliminary results obtained in a first shift of measurements, last June, are given. At the present stage of the data analysis, the authors can only draw some preliminary considerations. A wide band falling at around 240 nm is detected in all the analyzed samples. It intensity seems to decrease with increasing the dust collecting distance. A peak at 150 nm decreases in intensity with increasing the collecting distance. The band seems absent in the samples characterized by a larger amount of dust. A feature at about 200 nm is detected in some samples. At the moment the authors tend to attribute it to the transmission properties of the LiF substrates at the wavelength and/or to some problems in the experimental setup. It is unclear if a hump at 120 nm is real or due to instrumental effects. The profile of the spectra does not show substantial changes when the samples are cooled down to about 100 K. The present results appear to be in general agreement with previous findings, but their analysis is in progress and the interpretation is still on the way

Source/Load-Pull Noise Measurements at Ka Band

This paper is focused on the extraction of the noise parameters of a linear active device by exploiting both forward and reverse noise power measurements associated with different terminations. In order for load-pull measurements to yield a significant marginal improvement (as compared to forward measurements only) it is expected that the device under test should appreciably deviate from unidirectionality. For this reason, the source/load-pull technique is applied to frequencies at which the considered devices are still usable but their reverse noise factor exhibits a measurable dependence on the output terminations. Details on the test bench set up to the purpose, covering the 20–40 GHz frequency range, are provided. A characterization campaign on a 60 nm gate length, 4×35 µm GaN-on-Si HEMT fabricated by OMMIC is illustrated

Characterization and modelling of high-frequency active devices oriented to high-sensitivity subsystem design

In this chapter, quite a broad overview of noise characterization-related topics is offered to the reader, with different depth levels. Most of the attention, however, is paid to the practical side of noise measurements and the subsequent steps of noise extraction and modeling, as well as to some advanced design methodologies. A major concern is in the procedures that are necessary to effectively de-embed the measurements from the contribution of the test bench and the adopted methodologies. The scope of the discussion cover a well-assessed theory concerning linear devices operated in the frequency range from a few megahertz to some 100 GHz, and at physical temperatures above some tens of kelvins. In these conditions, 1/f noise can be neglected and Johnson (thermal) noise is approximately independent of frequency; as a consequence, thermal and, possibly, shot noise of elemental noise sources add up to yield a white power spectrum, which can be conveniently described in terms of “equivalent” thermal noise. The second part of the chapter is devoted to the application of the device noise models in the proper design of single- and multistage low noise amplifiers, including a mixed technique that actually employs characterization techniques directly in the amplifier design