Exploring the Charge Density Wave Phase of 1T-TaSe_{2}: Mott or Charge-Transfer Gap?

1T-TaSe_{2} is widely believed to host a Mott metal-insulator transition in the charge density wave (CDW) phase according to the spectroscopic observation of a band gap that extends across all momentum space. Previous investigations inferred that the occurrence of the Mott phase is limited to the surface only of bulk specimens, but recent analysis on thin samples revealed that the Mott-like behavior, observed in the monolayer, is rapidly suppressed with increasing thickness. Here, we report combined time- and angle-resolved photoemission spectroscopy and theoretical investigations of the electronic structure of 1T-TaSe_{2}. Our experimental results confirm the existence of a state above E_{F}, previously ascribed to the upper Hubbard band, and an overall band gap of ∼0.7 eV at Γ[over ¯]. However, supported by density functional theory calculations, we demonstrate that the origin of this state and the gap rests on band structure modifications induced by the CDW phase alone, without the need for Mott correlation effects.

Ultrafast spin-polarized electron dynamics in the unoccupied topological surface state of Bi2Se3.

The three-dimensional topological insulator Bi2Se3 presents two cone-like dispersive topological surface states centered at the [Formula: see text] point. One of them is unoccupied in equilibrium conditions and located 1.8 eV above the other one lying close to the Fermi level. In this work we employ time- and angle-resolved photoemission spectroscopy with circularly polarized pump photons to selectively track the spin dynamics of the empty topological states. We observe that spin-polarized electrons flow along the topological cone and recombine towards the unpolarized bulk states on a timescale of few tens of femtoseconds. This provides direct evidence of the capability to trigger a spin current with circularly polarized light.

Spin-Hall Voltage over a Large Length Scale in Bulk Germanium.

We exploit the spin-Hall effect to generate a uniform pure spin current in an epitaxial n-doped Ge channel, and we detect the electrically induced spin accumulation, transverse to the injected charge current density, with polar magneto-optical Kerr microscopy at a low temperature. We show that a large spin density up to 400 µm^{-3} can be achieved at the edges of the 100-µm-wide Ge channel for an applied electric field lower than 5 mV/µm. We find that the spin density linearly decreases toward the center of the Ge bar, due to the large spin diffusion length, and such a decay is much slower than the exponential one observed in III-V semiconductors, allowing very large spin accumulations over a length scale of tens of micrometers. This lays the foundation for multiterminal spintronic devices, where different spin voltages can be exploited as inputs for magnetologic gates on the same Ge platform.

Total plasma magnesium in healthy and critically ill foals.

Abnormalities in total Mg (tMg) concentration in plasma and/or serum are common in critically ill humans, and the association with increased mortality has been documented in several clinical studies in adults and newborns with hypoxic-ischemic encephalopathy. Abnormalities in tMg were studied in hospitalized dogs, cats, and adult horses. Newborn foals were scarcely studied with regard to Mg concentration. The aims of the present study were: (1) to compare two analytical methods for the determination of tMg in plasma: the automated colorimetric method and the atomic absorption spectrometry; (2) to measure plasma tMg in healthy foals during the first 72 hours after birth and in sick foals during the first 72 hours of hospitalization; (3) to compare total plasma Mg concentration among healthy foals, foals affected by perinatal asphyxia syndrome (PAS), prematurity and/or dismaturity, and sepsis; (4) to evaluate tMg plasma concentration in surviving and non-surviving foals. One hundred seventeen foals were included in the study: 20 healthy and 97 sick foals. The automated method used in clinical practice probably overestimates plasma tMg. Due to its higher sensitivity and specificity, the atomic absorption spectrometry should be considered the method of choice from an analytical point of view, but requires an instrumentation not easily available in any laboratory and specific technical skills and competencies. Plasma tMg in healthy foals were included in the range 0.52 to 1.01 mmol/L and did not show any time-dependent change during the first 72 hours of life. In sick foals, tMg evaluated at T0 was statistically higher than tMg measured at subsequent times. Foals affected by PAS had a tMg at T0 significantly higher (P < 0.01) than healthy, septic, and premature and/or dysmature foals. The t test found significantly higher (P < 0.01) plasma tMg measured at T0 in non-surviving than in surviving foals. Plasma tMg could be a useful parameter for the diagnosis of PAS and the formulation of the prognosis in critically ill foals.

Coherent ultrafast spin-dynamics probed in three dimensional topological insulators.

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses' light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone.

A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics.

A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO2 single crystals as a benchmark.

An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments.

Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Time- and angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup.

Cadmium accumulation and antioxidant responses in Sparus aurata exposed to waterborne cadmium.

Cadmium (Cd), a nonessential trace element, is rapidly accumulated by most living organisms and subsequently exerts its toxicity at different molecular levels. This study exposed gilthead sea bream (Sparus aurata) to waterborne 0.1 mg/l Cd for 11 days and investigated the Cd accumulation pattern, lipid oxidation, and response of antioxidant defences. At the end of the experiment, mean Cd concentrations in gills and liver, the organs most prone to metal accumulation, were 209.4 and 371.7 ng/g ww, respectively. Muscle did not show any Cd retention during the 11 days of exposure. In liver, the cytosolic fraction of the metal was chelated into the nontoxic form by metallothionein (MT), a specific Cd-inducible protein. Zn and Cu concentrations were not influenced by Cd exposure. Glutathione (GSH) concentrations and the antioxidant enzyme activities of GSH reductase and GSH peroxidase showed an overall decreasing trend. In addition, lipid and aqueous hydroperoxide levels did not show any significant variation. Oxidative stress indirectly generated by Cd seems to be compensated for by the different biochemical systems tailored to decrease cellular damage. In particular, the negative effects of Cd accumulation in tissues were probably counteracted by the induction of MT.

A versatile apparatus for time-resolved photoemission spectroscopy via femtosecond pump-probe experiments.

A laser-based system for time-resolved photoemission spectroscopy using up to 6.2 eV photons is presented. The versatility of the laser source permits several combinations of pump and probe photon energies with pulse durations of 50-100 fs. The ultrahigh vacuum system, equipped with evaporators, a low energy electron diffraction system and an Auger spectrometer, grants the possibility to grow and characterize thin films in situ. The electron energy analyzer is a time-of-flight spectrometer with a multianode detector allowing high count rates. The performance of the whole experimental setup is investigated on Cu(100), Cu(111), and Ag(111) single crystals.

Cadmium accumulation and biochemical responses in Sparus aurata following sub-lethal Cd exposure.

Cadmium (Cd), a heavy metal with limited biological function, is widely distributed in the aquatic environment as a result of natural and anthropogenic activities. The effect of 4 and 11 days exposure of gilthead sea bream Sparus aurata to sub-lethal concentrations of Cd was evaluated as levels of Cd content and Cd-metallothionein (MT) presence in different organs. The possible genotoxic effect was also evaluated in erythrocytes by using the "comet assay", a promising tool for estimating DNA damage at the single-cell level. The results obtained show that in the controls, Cd content was significantly higher in gills compared to in liver, but the treatment of fish with 0.1mg/l Cd induced a stronger accumulation of metal in liver depending on the length of the exposure period. Cd traces were found in plasma, muscle and kidney. Cd forms complexes in the cytosol with MT only in the liver but Cd-MT content significantly increased after 11 days of exposure to the metal, while after 4 days of treatment the protein level was similar to the control. The "comet assay" performed on S. aurata eryhtrocytes isolated from fish treated for 4 and 11 days with 0.1mg/l Cd, showed that there was no DNA damage at both exposure periods.

Copper transporter 1, metallothionein and glutathione reductase genes are differentially expressed in tissues of sea bream (Sparus aurata) after exposure to dietary or waterborne copper.

The high affinity copper transporter 1 (Ctr1), metallothionein (MT) and glutathione reductase (GR) are essential for copper uptake, sequestration and defense respectively. Following rearing on a normal commercial diet (12.6+/-0.2 mg kg(-1) Cu), sea bream were fed an experimental control diet lacking mineral mix (7.7+/-0.3 mg kg(-1) Cu), an experimental diet enhanced with Cu (135+/-4 mg kg(-1) Cu) or an experimental diet (7.7+/-0.3 mg kg(-1) Cu) whilst exposed to Cu in water (0.294+/-0.013 mg L(-1)). Fish were sampled at 0, 15 and 30 days after exposures. Fish fed the Cu-enhanced experimental diet showed lower levels of expression of Ctr1 in the intestine and liver compared to fish fed control experimental diets, whilst Ctr1 expression in the gill and kidney was unaffected by excess dietary Cu exposure. Waterborne-Cu exposure increased Ctr1 mRNA levels in the intestine and the kidney compared to experimental controls. Excess dietary Cu exposure had no effect on levels of metallothionein (MT) mRNA, and the only effect of dietary excess Cu on glutathione reductase (GR) mRNA was a decrease in the intestine. Both MT mRNA and GR were increased in the liver and gill after waterborne-Cu exposure, compared to levels in fish fed experimental control low Cu diets. Thus, Ctr1, MT and GR mRNA expression in response to excess Cu is dependent on the route of exposure. Furthermore, the tissue expression profile of sea bream Ctr1 is consistent with the known physiology of copper exposure in fish and indicates a role both in essential copper uptake and in avoidance of excess dietary and waterborne copper influx.

Effect of different organotins on DNA of mollusk (Scapharca inaequivalvis) erythrocytes assessed by the comet assay.

The alkaline comet assay, employing a single-cell gel-electrophoresis, is a rapid, simple and sensitive technique for visualizing and measuring DNA damage leading to strand breakage in individual cells. In this study, we report data about the effect of different organotin compounds (MBTC, DBTC and TBTC) on DNA from erythrocytes of the Scapharca inaequivalvis bivalve mollusc. Our results show significant DNA damage after 30 min in vitro incubation with 10microM of organotins. Since TBTC turned out to be the most genotoxic compound, followed by MBTC and DBTC, we exposed the molluscs to 50ppb of TBTC for 11 days. A significant increase of comet parameters was measured in our experimental conditions. The use of the comet test as a high-throughput screening assay to monitor the effect of environmental pollutants on marine organisms has been proposed.

Trace metals in arcid clam Scapharca inaequivalvis: effects of molluscan extracts on bioluminescent bacteria.

The relationship between a supposed effect of molluscan extracts on bioluminescent bacteria and metal concentrations in the extracts was investigated. For this purpose a biotoxicological assay based on bioluminescent bacteria (BLB) and extracts from metal exposed molluscs, Scapharca inaequivalvis, was optimized to monitor Cd and Cu marine pollution. Cu and Cd concentrations increased in tissues of experimentally exposed molluscs. Molluscan extracts inhibited the bacterial luminescence, the inhibition decreasing as the time of mollusc exposure to metals increased, suggesting a reduction of the "bioactive" metals. In regard to the use of BLB test in environmental monitoring, the analysis of Cu, Cd, and metallothionein (MT) was first performed in tissues from molluscs collected in three different areas of Northern Adriatic Sea. Metal concentrations reached maximum values in the gills, while Cd was mostly bound to MT in the kidney. Significant differences in metals and MT concentrations were found depending on the sampling sites. The biotoxicological assay resulted slightly correlated with the biochemical parameters.

Clinical and pathological findings of acute zinc intoxication in a puppy.

This report describes the clinical and pathological findings in a case of acute zinc poisoning in a young dog. The puppy suffered four days of progressively more severe vomiting and diarrhoea. Jaundice and pale mucous membranes, severe haematemesis and haemoglobinuria were other findings. Despite intensive therapy, the dog died a few hours after hospitalisation. Postmortem examination revealed a metallic foreign body in the stomach, catarrhal gastritis, hepatomegaly and enlarged, dark kidneys. Histology showed hepatic centrilobular vacuolar degeneration, haemoglobinuric nephrosis with early tubular necrosis, haemosiderosis and extramedullary haematopoiesis, as well as neuronal damage. The foreign body was mainly composed of zinc. Plasma zinc values were markedly raised (34.5 microg/ml; normal range 0.8 to 1.0 microg/ml). Pathophysiological mechanisms of zinc poisoning are discussed.

Immune-endocrine status and coeliac disease in children with Down's syndrome: relationships with zinc and cognitive efficiency.

Immune defects, thyroid abnormalities, plasma zinc levels, and the presence of gastrointestinal disease were investigated in 43 children with Down's syndrome (DS). Peripheral T lymphocytes with the phenotype of helper cells or cluster of differentiation 4 (CD4) were decreased. Circulating activated T cells (CD3/HLA-DR-positive cells) and large granular lymphocytes (CD16/CD56 positive cells) were increased. Plasma levels of interleukin-6 were higher in DS children than in controls. Serum levels of thyroid-stimulating hormone were increased in DS. Coeliac disease was over-represented in the group of DS children and many of these children also showed increased serum levels of immunoglobulin-G (IgG) specific for gliadin antigen. The increment of serum interleukin-6 was age-related and correlated with anti-gliadin IgG levels in DS. Plasma zinc levels were lower in DS children with coeliac disease and in those with anti-gliadin IgG than in DS without detectable anti-gliadin IgG. Dietary antigens may represent a continuous stimulus for the immune system in this syndrome and interfere with normal immune responses. Altered intestinal absorption of nutrients may in turn affect endocrine functions, brain development, and cognitive performances.

Localization of metallothionein I-II immunoreactivity in bovine pituitary gland.

Metallothioneins belong to a family of shock proteins characterized by an unusual high content of cystein, absence of aromatic amino acids and high metal content (Zinc and Copper). Metallothioneins are ubiquitously present in a large variety of prokaryotic and eukaryotic species as well as in all mammalian organs and tissues examined thus far. To the best of our knowledge this is the first report describing the presence of metallothioneins in the pituitary gland. Metallothioneins were identified immunohistochemically and chromatographically both in the neuro and adenohypophysis of the bovine pituitary gland. Metallothioneins are highly expressed in the neurohypophyseal glial cells, and in a subpopulation of folliculo-stellate cells located in the pars intermedia of the adenohypophysis. While the specific role of these proteins in the pituitary gland remains to be established, we hypothesize that, besides their protective action against free radicals, hypophyseal metallothioneins might be involved in the regulation of metal ion homeostasis with putative implication in release of hypothalamic peptide hormones in the neurohypophysis and synthesis/release of alpha-MSH by POMC-cells located in the pars intermedia of the adenohypophysis.