Ocular hypertension in myopia: analysis of contrast sensitivity

Purpose: we evaluated the evolution of contrast sensitivity reduction in patients affected by ocular hypertension and glaucoma, with low to moderate myopia. We also evaluated the relationship between contrast sensitivity and mean deviation of visual field. Material and methods: 158 patients (316 eyes), aged between 38 and 57 years old, were enrolled and divided into 4 groups: emmetropes, myopes, myopes with ocular hypertension (IOP≥21 ±2 mmHg), myopes with glaucoma. All patients underwent anamnestic and complete eye evaluation, tonometric curves with Goldmann’s applanation tonometer, cup/disc ratio evaluation, gonioscopy by Goldmann’s three-mirrors lens, automated perimetry (Humphrey 30-2 full-threshold test) and contrast sensitivity evaluation by Pelli-Robson charts. A contrast sensitivity under 1,8 Logarithm of the Minimum Angle of Resolution (LogMAR) was considered abnormal. Results: contrast sensitivity was reduced in the group of myopes with ocular hypertension (1,788 LogMAR) and in the group of myopes with glaucoma (1,743 LogMAR), while it was preserved in the group of myopes (2,069 LogMAR) and in the group of emmetropes (1,990 LogMAR). We also found a strong correlation between contrast sensitivity reduction and mean deviation of visual fields in myopes with glaucoma (coefficient relation = 0.86) and in myopes with ocular hypertension (coefficient relation = 0.78). Conclusions: the contrast sensitivity assessment performed by the Pelli-Robson test should be performed in all patients with middle-grade myopia, ocular hypertension and optic disc suspected for glaucoma, as it may be useful in the early diagnosis of the disease. Introduction Contrast can be defined as the ability of the eye to discriminate differences in luminance between the stimulus and the background. The sensitivity to contrast is represented by the inverse of the minimal contrast necessary to make an object visible; the lower the contrast the greater the sensitivity, and the other way around. Contrast sensitivity is a fundamental aspect of vision together with visual acuity: the latter defines the smallest spatial detail that the subject manages to discriminate under optimal conditions, but it only provides information about the size of the stimulus that the eye is capable to perceive; instead, the evaluation of contrast sensitivity provides information not obtainable with only the measurement of visual acuity, as it establishes the minimum difference in luminance that must be present between the stimulus and its background so that the retina is adequately stimulated to perceive the stimulus itself. The clinical methods of examining contrast sensitivity (lattices, luminance gradients, variable-contrast optotypic tables and lowcontrast optotypic tables) relate the two parameters on which the ability to distinctly perceive an object depends, namely the different luminance degree of the two adjacent areas and the spatial frequency, which is linked to the size of the object. The measurement of contrast sensitivity becomes valuable in the diagnosis and follow up of some important eye conditions such as glaucoma. Studies show that contrast sensitivity can be related to data obtained with the visual perimetry, especially with the perimetric damage of the central area and of the optic nerve head

The boundary Riemann solver coming from the real vanishing viscosity approximation

We study a family of initial boundary value problems associated to mixed hyperbolic-parabolic systems: v^{\epsilon} _t + A (v^{\epsilon}, \epsilon v^{\epsilon}_x ) v^{\epsilon}_x = \epsilon B (v^{\epsilon} ) v^{\epsilon}_{xx} The conservative case is, in particular, included in the previous formulation. We suppose that the solutions $v^{\epsilon}$ to these problems converge to a unique limit. Also, it is assumed smallness of the total variation and other technical hypotheses and it is provided a complete characterization of the limit. The most interesting points are the following two. First, the boundary characteristic case is considered, i.e. one eigenvalue of $A$ can be $0$. Second, we take into account the possibility that $B$ is not invertible. To deal with this case, we take as hypotheses conditions that were introduced by Kawashima and Shizuta relying on physically meaningful examples. We also introduce a new condition of block linear degeneracy. We prove that, if it is not satisfied, then pathological behaviours may occur.Comment: 84 pages, 6 figures. Text changes in Sections 1 and 3.2.3. Added Section 3.1.2. Minor changes in other section

V4743 Sgr, a magnetic nova?

Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed shortly after it returned to quiescence, 2 and 3.5 years after the explosion. The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz, indicating that V4743 Sgr is most probably an intermediate polar (IP). The X-ray spectra have characteristics in common with known IPs, with a hard thermal plasma component that can be fitted only assuming a partially covering absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like component, whose temperature was close to that of the white dwarf (WD) in the supersoft X-ray phase following the outburst, but with flux by at least two orders of magnitude lower. In quiescent IPs, a soft X-ray flux component originates at times in the polar regions irradiated by an accretion column, but the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible origin different from accretion. We suggest that it may have been due to an atmospheric temperature gradient on the WD surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. An optical spectrum obtained with SALT 11.5 years after the outburst showed a prominent He II 4686A line and the Bowen blend, which reveal a very hot region, but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is the third post-outburst nova and IP candidate showing a low-luminosity supersoft component in the X-ray flux a few years after the outburst.Comment: 9 pages, 5 figures, accepted to MNRA

Overcoming the Main Barriers of Circular Economy Implementation through a New Visualization Tool for Circular Business Models

There is a huge gap between the broad concept of circular economy (CE) and its practical implementation in the industrial sector due to several types of barriers, which shall be led back to the lack of consistent and precise information about resources, products, and processes. Without a proper information flow, it is impossible to quantify circular initiatives, both in comparison with the actual linear situation or with circular alternative opportunities. A proper quantification of circular initiatives allows the assessment of economic, environmental and social benefits and the preventative identification of potential barriers and relative solutions, monitoring the risk associated with circular investments and supporting the decision-making process. This paper describes a new tool to ensure the quantification of circular initiatives and the method to define it. It is a new Circular Business Model (CBM) visualization tool, which overcomes the main limitations of the existing models able to explain CE concepts but not to boost its practical implementation in industry. The new CBM visualization tool can be adopted in every industrial sector to highlight circular opportunities that are still hidden or unexploited or to select the best CE strategy. The proposed CBM visualization tool differs from the previous diagrams in two main characteristics: (i) the possibility to quantify resource flows and important indicators representing energy consumption, environmental and social impact, and (ii) the focus, which is not only on the product, but on the whole system, involving also the process, the company and the entire supply chain. The methodology to adopt and adapt the proposed model to different scales is described in detail. To provide a practical example, the model was qualitatively applied to a generic technical product to highlight its potential in the identification and quantification of circular activities

New X-ray observations of the old nova CP Puppis and of the more recent nova V351 Pup

We present X-ray observations of the field containing Nova Puppis 1942 (CP Pup) and Nova Puppis 1991 (V351 Pup), done with ASCA in 1998, and with XMM-Newton in 2005. The X-ray and UV luminosity of CP Pup seem to have remained approximately constant since the last X-ray observations of the 1980'ies, while the optical luminosity has decreased. The X-ray properties of this nova are explained by a high mass white dwarf accreting at low rate, in agreement with the nova theory given the large amplitude and other characteristics of the 1942 outburst. Assuming a distance of 1600 pc, the X-ray luminosity of CP Pup is L=2.2 x 10(33) erg/s in the 0.15-10 keV range covered with EPIC, compatible with a magnetic system. The RGS grating spectrum shows a few prominent emission lines, and it is fitted with a cooling flow with mass accretion rate mdot <= 1.6 x 10(-10) msol/year. We detected also the O VII complex at 21.6-21.8 A that does not arise in the cooling flow. Most likely this feature originates in a wind or in the nova shell. The RGS and EPIC spectra are fitted only with thermal models with a very high shock temperature, T>60 keV, indicating a white dwarf with M>1.1 M(sun). The X-ray flux is modulated with the spectroscopic period of 1.47 hours detected in the optical. Since CP Pup is not an eclipsing system, this is better understood if magnetic accretion occurs: we discuss this possibility and its implications in detail. V351 Pup (N Pup 1991) was detected with XMM-Newton, but not with ASCA. It is a faint, non-super-soft X-ray source with luminosity L(x) =~ 3 x 10(31) erg/s, a factor of 50 less than measured with ROSAT in 1993.Comment: in press on the Astrophysical Journa