Metal-insulator transition in single crystalline ZnO nanowires.

In this work, we report on the metal-insulator transition and electronic transport properties of single crystalline ZnO nanowires synthetized by means of Chemical Vapor Deposition. After evaluating the effect of adsorbed species on transport properties, the thermally activated conduction mechanism was investigated by temperature-dependent measurements in the range 81.7-250 K revealing that the electronic transport mechanism in these nanostructures is in good agreement with the presence of two thermally activated conduction channels. More importantly, it was observed that the electrical properties of ZnO NWs can be tuned from semiconducting to metallic-like as a function of temperature with a metal-to-insulator transition (MIT) observed at a critical temperature above room temperature (T c âˆ¼ 365 K). Charge density and mobility were investigated by means of field effect measurements in NW field-effect transistor configuration. Results evidenced that the peculiar electronic transport properties of ZnO NWs are related to the high intrinsic n-type doping of these nanostructures that is responsible, at room temperature, of a charge carrier density that lays just below the critical concentration for the MIT. This work shows that native defects, Coulomb interactions and surface states influenced by adsorbed species can significantly influence charge transport in NWs.

Dysmetabolic adipose tissue in obesity: morphological and functional characteristics of adipose stem cells and mature adipocytes in healthy and unhealthy obese subjects.

The way by which subcutaneous adipose tissue (SAT) expands and undergoes remodeling by storing excess lipids through expansion of adipocytes (hypertrophy) or recruitment of new precursor cells (hyperplasia) impacts the risk of developing cardiometabolic and respiratory diseases. In unhealthy obese subjects, insulin resistance, type 2 diabetes, hypertension, and obstructive sleep apnoea are typically associated with pathologic SAT remodeling characterized by adipocyte hypertrophy, as well as chronic inflammation, hypoxia, increased visceral adipose tissue (VAT), and fatty liver. In contrast, metabolically healthy obese individuals are generally associated with SAT development characterized by the presence of smaller and numerous mature adipocytes, and a lower degree of VAT inflammation and ectopic fat accumulation. The remodeling of SAT and VAT is under genetic regulation and influenced by inherent depot-specific differences of adipose tissue-derived stem cells (ASCs). ASCs have multiple functions such as cell renewal, adipogenic capacity, and angiogenic properties, and secrete a variety of bioactive molecules involved in vascular and extracellular matrix remodeling. Understanding the mechanisms regulating the proliferative and adipogenic capacity of ASCs from SAT and VAT in response to excess calorie intake has become a focus of interest over recent decades. Here, we summarize current knowledge about the biological mechanisms able to foster or impair the recruitment and adipogenic differentiation of ASCs during SAT and VAT development, which regulate body fat distribution and favorable or unfavorable metabolic responses.

Hydrothermally grown ZnO nanowire array as an oxygen vacancies reservoir for improved resistive switching.

Resistive switching (RS) devices based on self-assembled nanowires (NWs) and nanorods (NRs) represent a fascinating alternative to conventional devices with thin film structure. The high surface-to-volume ratio may indeed provide the possibility of modulating their functionalities through surface effects. However, devices based on NWs usually suffer from low resistive switching performances in terms of operating voltages, endurance and retention capabilities. In this work, we report on the resistive switching behaviour of ZnO NW arrays, grown by hydrothermal synthesis, that exhibit stable, bipolar resistive switching characterized by SET/RESET voltages lower than 3 V, endurance higher than 1100 cycles and resistance state retention of more than 105 s. The physical mechanism underlying these RS performances can be ascribed to nanoionic processes involving the formation/rupture of conductive paths assisted by oxygen-related species in the ZnO active layer. The reported results represent, to the best of our knowledge, the best resistive switching performances observed in ZnO NW arrays in terms of endurance and retention.

Resistive switching in sub-micrometric ZnO polycrystalline films.

Resistive switching (RS) devices are considered as the most promising alternative to conventional random access memories. They interestingly offer effective properties in terms of device scalability, low power-consumption, fast read/write operations, high endurance and state retention. Moreover, neuromorphic circuits and synapse-like devices are envisaged with RS modeled as memristors, opening the route toward beyond-Von Neumann computing architectures and intelligent systems. This work investigates how the RS properties of zinc oxide thin films are related to both sputtering deposition process and device configuration, i.e. valence change memory and electrochemical metallization memory (ECM). Different devices, with an oxide thickness ranging from 50-250 nm, are fabricated and deeply characterized. The electrical characterization evidences that, differently from typical nanoscale amorphous oxides employed for resistive RAMs (HfO x , WO x , etc), sub-micrometric thicknesses of polycrystalline ZnO layers with ECM configuration are needed to achieve the most reliable devices. The obtained results are deeply discussed, correlating the RS mechanism to material nanostructure.

Long-acting insulin analog detemir displays reduced effects on adipocyte differentiation of human subcutaneous and visceral adipose stem cells.

BACKGROUND AND AIMS: Since treatment with insulin detemir results in a lower weight gain compared to human insulin, we investigated whether detemir is associated with lower ability to promote adipogenesis and/or lipogenesis in human adipose stem cells (ASC). METHODS AND RESULTS: Human ASC isolated from both the subcutaneous and visceral adipose tissues were differentiated for 30 days in the presence of human insulin or insulin detemir. Nile Red and Oil-Red-O staining were used to quantify the rate of ASC conversion to adipocytes and lipid accumulation, respectively. mRNA expression levels of early genes, including Fos and Cebpb, as well as of lipogenic and adipogenic genes, were measured at various phases of differentiation by qRT-PCR. Activation of insulin signaling was assessed by immunoblotting. ASC isolated from subcutaneous and visceral adipose tissue were less differentiated when exposed to insulin detemir compared to human insulin, showing lower rates of adipocyte conversion, reduced triglyceride accumulation, and impaired expression of late-phase adipocyte marker genes, such as Pparg2, Slc2a4, Adipoq, and Cidec. However, no differences in activation of insulin receptor, Akt and Erk and induction of the early genes Fos and Cebpb were observed between insulin detemir and human insulin. CONCLUSION: Insulin detemir displays reduced induction of the Pparg2 adipocyte master gene and diminished effects on adipocyte differentiation and lipogenesis in human subcutaneous and visceral ASC, in spite of normal activation of proximal insulin signaling reactions. These characteristics of insulin detemir may be of potential relevance to its weight-sparing effects observed in the clinical setting.

[Metabolomic profiles of exhaled breath condensate of 39 nickel exposed workers]. / Profili metabolomici del condensato espiratorio di 39 lavoratori esposti a nichel.

Nickel compounds have proven lung carcinogenic effects and their processing involve a large amount of population. The aim of this study was to investigate the metabolomic profiles of Exhaled Breath Condensate (EBC) of a group of nickel exposed workers. Nickel in blood, urine and EBC of 39 workers (electroplaters) and 50 controls was measured. The 10 most nickel exposed workers were chosen for the analysis of EBC metabolomic profiles, matched to controls by gender and smoke habits. All the samples were analyzed using the HPLC-MS/MS system (High-Performance Liquid Chromatography/Mass Spectrometry). The profiles of the spectra obtained by the mass spectrometer (Orbitrap) analysis were processed using the MZmine 2.4 software. Nickel concentrations in EBC of the exposed workers were significantly higher compared to controls (1.39 microg/L; 0.039 microg/L, p = 0.017). The observation of the metabolomic profiles pointed out a significantly different response pattern between the exposed and the controls. This result was further studied by a subsequent processing with the XCMS program: an overexpression of 3 hypothetical substances in controls compared to exposed was detected. Although these data must be considered as preliminary, it has been observed that the mass-to-charge ratio of one of these substances may respond to the Phenylacethylglutamine (PAG) one, whose role in the control of cellular cycle is controversial and uncertain. Even if further studies to confirm these results are necessary, the analysis of the metabolomic profiles in the biological matrices is supposed to provide useful information both in the clinical and in the prevention fields.

[Health surveillance on workers exposed to wood dust: usefulness of the assessment of the nasal mucosa]. / Sorveglianza sanitaria negli esposti a polveri di legno: utilità della valutazione della mucosa nasale.

The purpose of this paper is to evaluate alterations in the nasal mucosa in workers that for professional purpose, are exposed, for a long period of time, to wood dust (WD). The increased frequency in alterations could underline a mechanism for chronic damage that could lead to cancer This study took into account 50 cabinet workers (EW) who had been exposed to WD for an average of 33 years and were compared to 48 controls (CC). A questionnaire regarding nasal symptoms was submitted, the nasal mucosa was examined by fibroscopy, secretions were valuated, cytogram from a nasal swap was also done. 44% of the EW and 33.4% of CC showed macroscopic alterations of the mucosa (PR 1,32 IC95% 0,79-2,19). The cytogram was altered in 24% of EW and in 12.5% of CC (PR 1,92 IC95% 0,78-4,71). In EW there was an abnormal significant increase in nasal secretions compared to CS, 28% vs 11,4% (PR 2,69 IC95% 1,05-6,89). The results do not confirm our hypothesis, but they show an unexpected prevalence of alteration in the CC. While waiting for further results, we express doubts in proposing routinary specialistic evaluation to all the EW to WD. At present it is hard to pin point indicators that could help reach an early diagnosis in the development of sinus-nasal cancer.

[Study of the olfactory function of a group of workers with significant lead exposure]. / Studio della funzione olfattiva di un gruppo di lavoratori con rilevante esposizione a piombo.

The aims of this study are to verify the potential lead damage on olfactory function and to identify early effects due to lead exposure. Our diagnostic evaluation included: (i) questionnaire to collect data about work and clinical history, (ii) olfactory evaluation: threshold test (Single-Starcaise) and identification/discrimination test (Wright). Lead exposure was evaluated by air sampling and biological monitoring (PbB, lead in blood). A sample of 18 exposed workers (mean age: 41.3 +/- 7.8; years exposure: 8.38 +/- 6) and of 39 controls (mean age: 41.9 +/- 9.7) were evaluated. The comparison between the threshold test of two groups confirmed a worse olfactory function in exposed (-4.97 log(10)vol/vol) compared to controls (-6.37 log(10)vol/vol), while the Wright test didn't show any significant correlation. The study didn't find a significant association between individual PbB levels and the threshold test. Knowledge of the effect of chronic occupational exposure to industrial chemicals on olfactory function is largely incomplete, but supports the hypothesis that olfactory neuroepithelium is susceptible to environmental exposures to chemicals. Occupational-related olfactory impairment is usually sub-clinical, and can be only detected using adeguate quantitative olfactory function testing procedures for quality research in this field.

Sialic acid measurement by a modified Aminoff method: a time-saving reduction in 2-thiobarbituric acid concentration.

Our results show that if the 2-thiobarbituric acid concentration is decreased, its co-precipitation with the chromophore is diminished. Subsequent running of this reaction mixture by high-performance liquid chromatography still allows measurement of Neu-5-Ac in the picomole order, with a substantial time and reactive saving, as compared with the original assay.

Microfluidics based on ZnO/nanocrystalline diamond surface acoustic wave devices.

Surface acoustic wave (SAW) devices with 64 µm wavelength were fabricated on a zinc oxide (ZnO) film deposited on top of an ultra-smooth nanocrystalline diamond (UNCD) layer. The smooth surface of the UNCD film allowed the growth of the ZnO film with excellent c-axis orientation and low surface roughness, suitable for SAW fabrication, and could restrain the wave from significantly dissipating into the substrate. The frequency response of the fabricated devices was characterized and a Rayleigh mode was observed at ∼65.4 MHz. This mode was utilised to demonstrate that the ZnO/UNCD SAW device can be successfully used for microfluidic applications. Streaming, pumping, and jetting using microdroplets of 0.5 and 20 µl were achieved and characterized under different powers applied to the SAW device, focusing more on the jetting behaviors induced by the ZnO SAW.

Bioleaching of metallic sulphides withThiobacillus ferrooxidans in the absence of iron (II).

Bioleaching of metallic sulphides withThiobacillus ferrooxidans in the absence of iron (II) was studied using pure sulphides and mixtures. The direct mode of bacterial action was analysed with respect to sulphide solubility, exposed solid surfaces and bacterial attachment to the solids. Bioleaching of mixed sulphides showed enhancement of metal extraction in comparison with pure sulphides which suggests metal extractions would be better from polymetallic sulphide ores than from similar matrices with only one sulphide.

Cholinergic modulation of growth hormone-releasing hormone effects on growth hormone secretion in dementia.

An impairment of cholinergic and somatostatinergic neurotransmission have been reported in dementia. Both acetylcholine and somatostatin are involved in the regulation of growth hormone (GH) secretion. The effects of GH-releasing hormone (GHRH) 1-44 on GH release have been studied before and after the pretreatment with pyridostigmine or pirenzepine in subjects with senile dementia of the Alzheimer type, multi-infarct dementia and mixed dementia. The data have been compared with those obtained in an age-matched healthy control group. The GH response to GHRH is similar in the patients and in the controls, though the peak occurrence is significantly delayed in dementia. The cholinesterase inhibitor pyridostigmine enhances significantly the GH response to GHRH in both groups. The responses obtained in demented subjects are significantly larger than those found in the controls. Pirenzepine, a muscarinic receptor blocker, inhibits the GHRH effect on GH secretion in both groups. The findings may be interpreted in terms of an underlying impairment of the hypothalamic cholinergic neurotransmission, with an acetylcholine receptor supersensitivity that becomes apparent when the cholinergic tonus is enhanced by the inhibition of cholinesterase by pyridostigmine. No significant differences, due to the type of dementia, have been observed.

Effects of pyridostigmine, corticotropin-releasing hormone and growth hormone-releasing hormone on the pituitary-adrenal axis and on growth hormone secretion in dementia.

Alterations of neuroendocrinological indices determined by the impaired regulating effects of cholinergic neurotransmission have been described in primary dementia. In this study we have evaluated the effects of acetylcholinesterase inhibition by pyridostigmine on growth hormone (GH), adrenocorticotropic hormone (ACTH) and cortisol secretion and on their responses to GH-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) in 7 patients with primary degenerative dementia and in 8 sex- and age-matched controls. Demented subjects showed higher cortisol basal levels and lower ACTH levels than controls. Pyridostigmine increased the GH response to GHRH in both groups, the effect being significantly enhanced in patients. An increase of ACTH and cortisol levels was found in both groups after pyridostigmine and CRH administration. Pyridostigmine pretreatment significantly increased the ACTH response to CRH in controls but not in patients. The obtained data may indicate that a muscarinic receptor upregulation and an impairment of somatostatinergic function are operative in the regulation of GH secretion in dementia. An underlying hyperactivity of the hypothalamic-pituitary-adrenal axis impairs the responses of ACTH and cortisol to CRH in this disorder.