Plasmon Modes of Graphene Nanoribbons with Periodic Planar Arrangements.

Among their amazing properties, graphene and related low-dimensional materials show quantized charge-density fluctuations-known as plasmons-when exposed to photons or electrons of suitable energies. Graphene nanoribbons offer an enhanced tunability of these resonant modes, due to their geometrically controllable band gaps. The formidable effort made over recent years in developing graphene-based technologies is however weakened by a lack of predictive modeling approaches that draw upon available ab initio methods. An example of such a framework is presented here, focusing on narrow-width graphene nanoribbons, organized in periodic planar arrays. Time-dependent density-functional calculations reveal unprecedented plasmon modes of different nature at visible to infrared energies. Specifically, semimetallic (zigzag) nanoribbons display an intraband plasmon following the energy-momentum dispersion of a two-dimensional electron gas. Semiconducting (armchair) nanoribbons are instead characterized by two distinct intraband and interband plasmons, whose fascinating interplay is extremely responsive to either injection of charge carriers or increase in electronic temperature. These oscillations share some common trends with recent nanoinfrared imaging of confined edge and surface plasmon modes detected in graphene nanoribbons of 100-500 nm width.

Increased left atrial size in obese children and its association with insulin resistance: a pilot study.

Subclinical cardiac abnormalities represent predisposing factors for cardiovascular disease (CVD) in obese subjects. The aim of this study was to evaluate early cardiac abnormalities in obese youth and the potential association with insulin resistance (IR). Thirty obese (12 males (M)/18 females (F); age = 11.5 ± 2.4 years; body mass index (BMI)-standard deviation score (SDS) = +2.1 ± 0.5) and 15 normal weight (10 M/5 F; age = 12.8 ± 3.1 years; BMI-SDS = +0.3 ± 0.9) children and adolescents underwent Doppler two-dimensional echocardiographic assessments of left atrial (LA) and ventricular (LV) geometry and LV diastolic function (peak early [E] and late waves, E wave deceleration time, myocardial flow velocities). Homeostasis model assessment of IR (HOMA-IR) was used as an IR index. LA size was increased in obese children, as indicated by higher LA diameter (4.9 ± 0.5 vs 4.1 ± 0.4 cm, p < 0.001), area (14.3 ± 2.5 vs 10.7 ± 2.0 cm(2), p < 0.001), and volume (33.8 ± 10.6 vs 23.7 ± 6.4 ml, p = 0.003). LV mass was also increased in obese children (87.0 ± 16.6 vs 68.8 ± 13.2 g, p = 0.003), who also showed subtle diastolic dysfunctions, as indicated by higher values of E (97.1 ± 14.3 vs 86.2 ± 11.9 cm/s, p = 0.02). All the above parameters were significantly associated with BMI-SDS (p < 0.05). In addition, HOMA-IR was independently associated with LA diameter, area, and volume (ß = 0.314, p = 0.040; ß = 0.415, p = 0.008; ß = 0.535, p = 0.001). CONCLUSION: Obese children feature increased LA size, which emerged to be mainly correlated to, and possibly driven by IR, suggesting an increased CVD risk. WHAT IS KNOWN: Left atrial and ventricular alterations have been reported in obese adults, and they represent predisposing factors for cardiovascular disease. There is some evidence suggesting that obese children show increased left ventricular mass and also increased atrial size, although with conflicting results. WHAT IS NEW: Obese normotensive children showed a moderately increased atrial size, subtle alterations in left cardiac diastolic function, and ventricular mass. An association between insulin resistance and left cardiac changes was found, although its mechanism remains to be determined.

Parasellar myxoid chondrosarcoma: a rare variant of cranial chondrosarcoma.

Primary cranial chondrosarcoma in an uncommon cartilaginous tumours of which the myxoid variant is the least reported in the literature. This tumour accounts for 0.15% of all primary intracranial lesions and 6% of all skull base tumours. Chondrosarcomas are frequently misdiagnosed as chordomas, which have a different prognosis. Differential diagnosis is very important because, when treated with similar aggressive treatment strategies, chondrosarcoma has a much better prognosis than chordoma. We describe a 54-year-old female with a 9-month history of left ophtalmoplegia and increasing headache. MR imaging of the head showed a sellar and left parasellar mass. We performed a gross total removal of the mass via a left pterional approach. The histopathologic diagnosis was of a myxoid chondrosarcoma. A post-operative contrast-enhanced computed tomography (CT) scan of the head showed a total removal of the neoplasm. After surgery, the patient showed a transitory dysphasia with right hemiparesis, but they both considerably improved before discharge. Review of the literature was identified using the Medline database: only 10 cases in the worldwide literature were identified to report on this kind of tumour. We present a case report of myxoid chondrosarcoma, a rare variant of chondrosarcoma, with sellar and left parasellar localization. This histopathological type is a low-grade variant and its total removal is effective.

Spontaneous chronic subdural hematoma in a young adult.

Chronic subdural hematoma (CSDH) is a common pathology in the elderly but very rare in young adults. When CSDH occurs in this age group, severe head injury or some promotive factors are usually present. This article reports the case of a 29-year-old female presented at our Emergency Department with a few days' history of progressive frontal headache. Computed tomography scan of the head showed a right frontal CSDH. Only a decreased level of consciousness without focal deficits was present at clinical examination and her medical history was negative for trauma or promotive factors. Blood count showed a mild sideropenic anemia while coagulation tests were normal. No vascular malformations were shown at digital subtraction angiography. The patient underwent craniotomic evacuation. After surgery, the patient showed a full neurological recovery. Spontaneous CSDH in young adults is very rare. In the worldwide literature, many cases of non-traumatic CSDH are reported, but a promotive factor is generally present. We described a case of spontaneous CSDH, whose etiology remains unknown.

[Elevated levels of lipoprotein(a) are present in subjects with early ischemic cardiopathy and with a familial history of ischemic cardiopathy]. / Più elevati livelli di lipoproteina(a) sono presenti in soggetti con cardiopatia ischemica precoce e con storia familiare di cardiopatia ischemica.

BACKGROUND: Elevated levels of lipoprotein(a) are associated with a greater risk of atherothrombotic cardiovascular diseases. Since the Lp(a) levels are genetically determined and fairly stable in the course of life and a family history appears to be an independent risk factor of cardiovascular diseases, we evaluated the behavior of Lp(a) levels in patients with early events of coronary heart disease (CHD) and also in subjects with positive family history of ischemic heart diseases. METHODS: The levels of lipoprotein (a) [Lp(a)] were measured in 254 subjects, 138 males and 116 females with an average age of 48.6 +/- 13.8 years (range 20-76 years). Diabetic subjects, females submitted to oestrogen treatment and those already in treatment with hypolipidaemic drugs were excluded from the study. Forty of the 254 patients (15.7%), 27 males and 13 females, had CHD (29 a previous myocardial infarction and 11 a stable angina). A positive family history for CHD was considered present (102 of the 254 patients) if one or more first degree relatives had angina or myocardial infarction before the age of 60 years in men and 65 in women. RESULTS: The levels of Lp(a) were higher (p < 0.01) in women (25.1 +/- 28.3 mg/dl) compared to men (17.6 +/- 18.4 mg/dl), without differences in relation to age. The Lp(a) plasmatic levels were not correlated with age, body mass index, total cholesterol, LDL and HDL, triglycerides, apo B, apo AI, fibrinogen and there were no differences in Lp(a) levels in presence or absence of other known cardiovascular risk factors such as hypertension and smoking. The Lp(a) levels were not different between subjects with CHD (28.15 +/- 31.7 mg/dl) and controls (20.3 +/- 22.8 mg/dl). The subjects with CHD were older and had higher levels of fibrinogen and a significantly greater prevalence of hypertension and family history of CHD. Fifteen of the 40 subjects with CHD had an early onset of CHD (before 50 years of age) and only in such patients the Lp(a) levels were significantly greater compared to controls (35.8 +/- 33.2 mg/dl vs 20.3 +/- 22.8 of the controls, p < 0.01), independently of other variables (age, BMI, smoking, hypertension, cholesterol, triglycerides, HDL-c, LDL-c, fibrinogen). Furthermore the Lp(a) plasmatic levels were higher in subjects with a family history of CHD (28.3 +/- 27.6 mg/dl vs 16.3 +/- 18.6 mg/dl of the subjects without a family history of CHD, p < 0.01) even if they had or not had a previous coronary ischemic event. CONCLUSIONS: Such data confirm the importance of high levels of Lp(a) above all for the early events of CHD and for the subjects with a family history of CHD, which could be expression of a greater predisposition for cardiovascular events.

Testing the saprobity hypothesis in a Mediterranean lagoon: effects of confinement and organic enrichment on benthic communities.

The macrobenthic community was compared at four sites characterized by varying degrees of freshwater input, organic enrichment and confinement in the Cabras lagoon (Sardinia, Italy). Three sites, riverine (C1), confined (C2) and seaward (C3), were studied on two dates of summer 2010 and on two dates of winter 2011. A fourth site (C12), representative of the central sector of the Cabras lagoon, was included in this study using the extensive historical datasets at our disposal from previously published work. We aimed to test the hypothesis that (1) the benthos is distributed according to the recently proposed concept of habitat saprobity for coastal lagoons that unifies the Pearson-Rosenberg (sensu organic enrichment) and Guélorget-Perthuisot (sensu confinement) models, and (2) indicator species of different saprobic levels can be identified among dominant species occurring along the saprobity gradient. Salinity was also considered as an additional agent of selection in brackish environments. Irrespective of significant seasonal changes within each site, our results highlighted major environmental and biotic differences between sites. At the northward riverine site (C1), most affected by freshwater input and with limited organic matter (OM) enrichment, Corophium orientale was the single dominant species. The most confined site (C2) was characterized by the highest levels of sedimentary OM and benthic Chlorophyll-a and by mesohaline conditions; the site was inhabited mainly by the halolimnobic Hediste diversicolor and Hydrobia spp. Site C12, characterized by a high OM load and high residence time, was dominated by the opportunistic detritivorous Alitta succinea and Polydora ciliata. At the southernmost seaward site (C3) the considerable seawater renewal, resulting in high salinity (only in summer) and limited OM load, favored a much more diverse macrobenthic assemblage, essentially composed of both marine species, such as Corophium insidiosum, Gammarus aequicauda, and brackish-water species, such as Lekanesphaera hookeri and Idotea chelipes. We conclude that the biotic and abiotic characteristics of the Cabras lagoon can be represented by a succession of spatial zones along two main gradients determined by salinity and saprobity. The salinity gradient proved to be the main structural feature in the oligohaline pole, while in the range of variable salinity, saprobity appeared to be the main selection factor. To illustrate our findings, we provide a graphical representation summarizing the changes in environmental parameters and indicator species along the salinity and saprobity gradients.

Phase transitions in two-dimensional Z(N) vector models for N>4.

We investigate both analytically and numerically the renormalization group equations in two-dimensional (2D) Z(N) vector models. The position of the critical points of the two phase transitions for N>4 is established and the critical index ν is computed. For N=7 and 17 the critical points are located by Monte Carlo simulations, and some of the corresponding critical indices are determined. The behavior of the helicity modulus is studied for N=5, 7, and 17. Using these and other available Monte Carlo data we discuss the scaling of the critical points with N and some other open theoretical problems.

Phase transitions in strongly coupled three-dimensional Z(N) lattice gauge theories at finite temperature.

We perform an analytical and numerical study of the phase transitions in three-dimensional Z(N) lattice gauge theories at finite temperature for N>4, exploiting equivalence of these models with a generalized version of the two-dimensional vector Potts models in the limit of vanishing spatial coupling. In this limit the Polyakov loops play the role of Z(N) spins. The effective couplings of these two-dimensional spin models are calculated explicitly. It is argued that the effective spin models have two phase transitions of BKT type. This is confirmed by large-scale Monte Carlo simulations. Using a cluster algorithm we locate the position of the critical points and study the critical behavior across both phase transitions in details. In particular, we determine various critical indices and compute the helicity modulus, the average action, and the specific heat. A scaling formula for the critical points with N is proposed.

Numerical study of the phase transitions in the two-dimensional Z(5) vector model.

We investigate the critical properties of the two-dimensional Z(5) vector model. For this purpose, we propose a cluster algorithm, valid for Z(N) models with odd values of N. The two-dimensional Z(5) vector model is conjectured to exhibit two phase transitions with a massless intermediate phase. We locate the position of the critical points and study the critical behavior across both phase transitions in details. In particular, we determine various critical indices and compare the results with analytical predictions.

Natural selection associated with birth weight. II. Stabilizing and directional components.

The differences of birth-weight distributions before and after selection by the different components of perinatal mortality were studied for all single babies born in Italy in 1974. It was found that: (i) In mature babies the selection is mainly stabilizing while the directional type is almost negligible. (ii) In immature babies both stabilizing and directional selection are at work, greatly modifying the birth weight distributions.

Natural selection associated with birth weight. I. Selection intensity and selective deaths from birth to one month of life.

Differential mortality as a function of birth weight was studied up to the 4th week of life in all single births in Italy in 1974. It was found that: (i) Both selection intensity and selective mortality are much higher with increasing immaturity. (ii) For babies born at term or after 8 months of pregnancy selection intensity tends to relax as early as one week after birth, while for those born after 7 months selection is at work for a longer period. (iii) Selective mortality, on the other hand, keeps increasing after birth but its relevance is relatively decreasing since average mortality after birth continues to decrease.

Natural selection associated with birth weight. III. Changes over the last twenty years.

Differential stillbirth rates as a function of birth-weight have been studied in all single births in Italy in the years, 1954, 1961, 1967 and 1974. In the course of the twenty year interval of observation the following changes were found: (i) a progressive equalization of mortality in birth-weight classes near the mean; (ii) a reduction of the directional component of selection which is parallel to the increase of mean birth-weight (in the case of 8 months of pregnancy); (iii) a reduction of the stabilizing component of selection which is parallel to the decrease of birth-weight variance (in the case of 9 months of pregnancy); (iv) a reduction of selection intensity, while selective mortality remains more or less unchanged. The modifications of natural selection associated with birth-weight as consequence of health care progress in this population are also discussed.