Electronic properties and Schottky barriers at ZnO-metal interfaces from first principles.

First principles calculations were performed to study the interface electronic structure and the Schottky barrier heights (SBHs) of ZnO-metal interfaces. Different kinds of metals were considered with different chemistries on the polar (0 0 0 1) and (0 0 0 1¯) ZnO surfaces. The projection of the density of states on the atomic orbitals of the interface atoms reveals that two kinds of interface electronic states appear: states due to the chemical bonding which appear at well defined energies and conventional metal-induced gap states associated with a smooth density of states in the bulk ZnO band gap region. The relative weight and distribution of the two classes of states depend on both the ZnO substrate termination and on the metal species. SBHs are found to be very sensitive to the specific interface chemical bonding. In particular, it is possible to note the occurrence of either Schottky barriers or Ohmic contacts. Our results have been compared with experiments and with available phenomenological theories, which estimate the SBH from few characteristic material parameters. Finally, the electronic and structural contributions to the SBH have been singled out and related to the different charge transfers occurring at the different interfaces.

A population of fast radio bursts at cosmological distances.

Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x- or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.

Transformation of a star into a planet in a millisecond pulsar binary.

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.

Tests of general relativity from timing the double pulsar.

The double pulsar system PSR J0737-3039A/B is unique in that both neutron stars are detectable as radio pulsars. They are also known to have much higher mean orbital velocities and accelerations than those of other binary pulsars. The system is therefore a good candidate for testing Einstein's theory of general relativity and alternative theories of gravity in the strong-field regime. We report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. These tests use the theory-independent mass ratio of the two stars. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the "post-Keplerian" parameter s agrees with the value predicted by general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current solar system tests. It also implies that the second-born pulsar may not have formed through the core collapse of a helium star, as is usually assumed.

Transient radio bursts from rotating neutron stars.

The radio sky is relatively unexplored for transient signals, although the potential of radio-transient searches is high. This was demonstrated recently by the discovery of a previously unknown type of source, varying on timescales of minutes to hours. Here we report a search for radio sources that vary on much shorter timescales. We found eleven objects characterized by single, dispersed bursts having durations between 2 and 30 ms. The average time intervals between bursts range from 4 min to 3 h with radio emission typically detectable for <1 s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4-7 s for ten of the eleven sources, suggesting origins in rotating neutron stars. Despite the small number of sources detected at present, their ephemeral nature implies a total Galactic population significantly exceeding that of the regularly pulsing radio pulsars. Five of the ten sources have periods >4 s, and the rate of change of the pulse period has been measured for three of them; for one source, we have inferred a high magnetic field strength of 5 x 10(13) G. This suggests that the new population is related to other classes of isolated neutron stars observed at X-ray and gamma-ray wavelengths.

A double-pulsar system: a rare laboratory for relativistic gravity and plasma physics.

The clocklike properties of pulsars moving in the gravitational fields of their unseen neutron-star companions have allowed unique tests of general relativity and provided evidence for gravitational radiation. We report here the detection of the 2.8-second pulsar J0737-3039B as the companion to the 23-millisecond pulsar J0737-3039A in a highly relativistic double neutron star system, allowing unprecedented tests of fundamental gravitational physics. We observed a short eclipse of J0737-3039A by J0737-3039B and orbital modulation of the flux density and the pulse shape of J0737-3039B, probably because of the influence of J0737-3039A's energy flux on its magnetosphere. These effects will allow us to probe magneto-ionic properties of a pulsar magnetosphere.

An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system.

The merger of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity. A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low, because we know of only a few double-neutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737-3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737-3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe).

Heterologous expression and characterization of the exopolysaccharide from Streptococcus thermophilus Sfi39.

The genes responsible for exopolysaccharide (EPS) synthesis in Streptococcus thermophilus Sfi39 were identified on a 20-kb genomic fragment. The two genes, epsE and epsG, were shown to be involved in EPS synthesis as their disruption lead to the loss of the ropy phenotype. Several naturally selected nonropy mutants were isolated, one acquired an insertion sequence (IS)-element (IS905) in the middle of the eps gene cluster. The eps gene cluster was cloned and transferred into a nonEPS-producing heterologous host, Lactococcus lactis MG1363. The EPS produced was shown by chemical analysis and NMR spectroscopy to be identical to the EPS produced by S. thermophilus Sfi39. This demonstrated first that all genes needed for EPS production and export were present in the S. thermophilus Sfi39 eps gene cluster, and second that the heterologous production of an EPS was possible by transfer of the complete eps gene cluster alone, provided that the heterologous host possessed all necessary genetic information for precursor synthesis.

Molecular ecology of Streptococcus thermophilus bacteriophage infections in a cheese factory.

A mozzarella cheese factory using an undefined, milk-derived Streptococcus thermophilus starter system was monitored longitudinally for 2 years to determine whether the diversity of the resident bacteriophage population arose from environmental sources or from genetic changes in the resident phage in the factory. The two hypotheses led to different predictions about the genetic diversity of the phages. With respect to host range, 12 distinct phage types were observed. With two exceptions, phages belonging to different lytic groups showed clearly distinct restriction patterns and multiple isolates of phages showing the same host range exhibited identical or highly related restriction patterns. Sequencing studies in a conserved region of the phage genome revealed no point mutations in multiple isolates of the same phage type, while up to 12% nucleotide sequence diversity was observed between the different phage types. This diversity is as large as that between the most different sequences from phages in our collection. These observations make unlikely a model that postulates a single phage invasion event and diversification of the phage during its residence in the factory. In the second stage of our factory study, a defined starter system was introduced that could not propagate the resident factory phage population. Within a week, three new phage types were observed in the factory while the resident phage population was decreased but not eliminated. Raw milk was the most likely source of these new phages, as phages with identical host ranges and restriction patterns were isolated from raw milk delivered to the factory during the intervention trial. Apparently, all of the genetic diversity observed in the S. thermophilus phages isolated during our survey was already created in their natural environment. A better understanding of the raw-milk ecology of S. thermophilus phages is thus essential for successful practical phage control.

[Polydistrectual atherosclerosis in the elderly. Ischemic cardiopathy and obliterative peripheral arteriopathy of the lower limbs]. / Aterosclerosi polidistrettuale nell'anziano. Cardiopatia ischemica e arteriopatie obliteranti periferiche degli arti inferiori.

BACKGROUND: Numerous epidemiological studies have recently drawn attention to the polydistrict nature of atherosclerotic disease. In particular, it has been made clear the frequent association between coronary heart disease and peripheral arterial disease of the lower limbs. We have therefore evaluated the frequency of peripheral arterial disease in a consecutive unselected series of patients affected by coronary heart disease, over 65 and under 65. We have besides evaluated the frequency of some factors of risk for atherosclerotic disease on the subjects affected by coronary heart disease alone and in those with associated peripheral arterial disease. METHODS: We have studied 502 patients (280 males and 222 females) with coronary heart disease admitted to the II Division of General Medicine of Pugliese-Ciaccio Hospital of Catanzaro. Of the 502 patients examined, 367 (72.7%) over 65 and 137 (27.3%) under 65. Factors of risk considered were familiarity, cigarette smoking, diabetes mellitus, dyslipidosis, arterial hypertension. RESULTS AND CONCLUSIONS: Peripheral arterial disease was present in 37% of the subjects examined. In the elderly group there was a frequency of 87.6%, while in subjects under 65 the frequency was 12.4%. Symptoms of claudicatio were present in 100% of the subjects under 65 and 58.6% of the elderly subjects. Risk factors that apply with greater frequency were diabetes mellitus, arterial hypertension and smoking. The results of our study show the importance of searching for stenosis even if asymptomatic in patients with coronary heart disease, above all if elderly.

[Nailfold capillaroscopy in the study of microcirculation in childhood]. / La capillaroscopia periungueale nello studio del microcircolo in età pediatrica.

The nailfold capillaroscopy allows to study the microcirculation: for its simple and rapid execution it can be used also in children. We examined the nailfold capillaroscopy features in childhood and valued the maturation of microcirculation in connection to age and presented some pathologic patterns. We studied nailfold capillaroscopy patterns in sixty-six children without chronic cutaneous diseases. Our results showed that development of microcirculation during childhood is incomplete. In connection to age we observed the capillaries are arranged as arches in children younger than six months, there are disposed as saddles between 12 and 24 months and they became similar to those of the adult at about 10-11 years. We observed immature capillaries in one child with hypothyroidism and one's delay growth. The cutaneous hemorrhages were rarely found in children who bit the in nails. The capillaroscopy is helpful to value the maturation of the capillaries from the birth to the adolescence. Moreover we would like to underline how our children took part to this exam almost like as if it were a game.

Nail-fold capillaroscopy in the study of microcirculation in elderly hypertensive patients.

Hypertension represents one of the most important atherosclerotic risk factors, since it causes vascular damage both to macro- and microcirculation. Capillaroscopy is very useful to examine "in vivo" the small vessels of nail-fold and conjunctival layer of the bulb which are the most suitable areas for a morphological study of microcirculation. Capillaroscopy gives remarkable information from a clinical and diagnostic point of view, both in the diseases involving microcirculation (connective tissue disorders, diabetes) and in the evaluation of microvascular impairments in systemic diseases such as arterial hypertension. Aim of the present study was at evaluating capillaroscopic characteristics in a consecutive and non-selected series of elderly hypertensive patients and comparing the results to those observed on fundus oculi. Our study revealed the decrease of the number of capillary loops which appear thin and lengthened, in the hypertensive persons, as compared to the control group. Dilated and tortuous capillaries, arteriovenous sludge and "flea bite" juxtacapillary microhemorrhages were found more frequently in the patients with isolated systolic hypertension; they are linked to the atherosclerotic nature of that disease.

Aging and sex influence the permeability of the blood-brain barrier in the rat.

The aim of the present study was to investigate the existence of aging- and sex-related alterations in the permeability of the blood-brain barrier (BBB) in the rat, by calculating a unidirectional blood-to-brain transfer constant (Ki) for the circulating tracer [14C]-alpha-aminoisobutyric acid. We observed that: a) the permeability of the BBB significantly increased within the frontal and temporo-parietal cortex, hypothalamus and cerebellum in 28-30 week old rats, in comparison with younger animals; b) in several brain areas of female intact rats higher Ki values (even though not significantly different) were calculated at oestrus than at proestrus; c) in 1-week ovariectomized rats there was a marked increase of Ki values at the level of the frontal, temporo-parietal and occipital cortex, cerebellum and brain-stem. One can speculate that aging- and sex-related alterations in the permeability of the BBB reflect respectively changes in brain neurochemical system activity and in plasma steroid hormone levels.

[Liver pathology caused by drugs. Pathogenetic, histopathological and clinical notes and case reports]. / Patologia epatica da farmaci. Note patogenetiche, istopatologiche, cliniche e contributo casistico.

After a brief review of drug metabolic pathways in the liver, the various mechanisms leading to liver damage are described. The different histological lesions and the clinical situations that can arise are discussed. A case survey is reported.

[Antisalmonellal agglutination in liver cirrhosis and chronic hepatitis]. / Agglutinazione anti salmonelle nella cirrosi epatica e nelle epatiti croniche.

A positive serum diagnosis for Salmonellae was obtained in 7 patients with cirrhosis of the liver and 18 with chronic hepatitis (22 males and 3 females), even though their history was negative and they had not even been vaccinated against thyphus and paratyphus. The results are seen as a warning that laboratory data that might lead to a mistaken diagnosis and incorrect treatment should be interpreted with particular care.