Analysis of transport properties and photoconductive response of single InAs nanowires

Semiconductor nanowires are artificial structures of nanometer size with an approximately cylindric shape. They have an aspect ratio much larger than one so that, in most instances, they can be considered 1D systems. This peculiar property makes nanowires one of the most interesting technologies in the roadmap for the electronic downscaling. At the moment, however, they are still the object of scientific research and, even if nanowire transistor devices start to be investigated and developed, many physical aspects and characteristics are still to be investigated. In this thesis I have studied the transport properties of single nanowire transistors in a variety of configurations. The lateral-gate and the back-gate geometry were realized, measured and simulated using a finite element formalism. The simulation allowed the computation of electron mobility and charge density within the wires and the comparison among the results of different wire structures. Photoconductivity measurements were also attempted in order to directly explore the nanowire electronic band structure. The thesis is divided into four chapters. - Semiconductor nanowires In the first part I present the peculiarities of a semiconductor nanowire, discussing the features of the semiconductor material and the effect of the low dimensionality. Then I explain the growth process of the different kinds of nanowires used in this work (homogeneous and radially heterostructured). The nanowires were grown in the NEST laboratory with the Chemical Beam Epitaxy (CBE) technique. The realization of nanowires can be explained with the Vapor-Liquid-Solid (VLS) model for the growth mechanism involving the seed of a gold particle. After the growth an important stage is to check the nanowires produced by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray spectroscopy (EDAS). - Transport and optical properties in nanowires An introduction is given to the transport in the mesoscopic structures distinguishing between ballistic and diffusive transport. The specific case of InAs nanowires transport is taken in account, discussing all the main factors that affect transport (sample contacts, gate contact, temperature and nanowire size). A simple transport model is then presented for the single nanowire transistor configuration: with some approximations it is possible to estimate the electron mobility and the charge density in the wire. InAs is sensitive to mid-infrared light because of its small direct gap. After an overview on the electronic transitions related to photoconductivity, general properties of photoconductivity are described. Some photoconductivity experiments in the literature are reported. - Processing and experimental set-up The fabrication of a nanowire device requires many steps using photo-lithography and electron-lithography techniques. All steps are accurately described establishing a methodology for the single nanowire transistor configuration. Then the set-up for transport measurements is presented as well as the one for optical measurements. - Transport and photoconductivity measurements In the last part the transport and optical measurements are described. Transport results are discussed with the support of a finite element model that simulates the nanowire device. The model was developed in the case of a back-gate and a lateral-gate geometry in order to compute a more accurate capacitance of the nanowire-gate system. In this way a more reliable result on the electron mobility and charge density in the nanowire is estimated and compared with the literature results. First attempts to measure the photoconductive response of individual nanowire are also discussed examining in particular the influence of the substrate

The Emotion Probe: On the Universality of Cross-Linguistic and Cross-Gender Speech Emotion Recognition via Machine Learning

Machine Learning (ML) algorithms within a human–computer framework are the leading force in speech emotion recognition (SER). However, few studies explore cross-corpora aspects of SER; this work aims to explore the feasibility and characteristics of a cross-linguistic, cross-gender SER. Three ML classifiers (SVM, Naïve Bayes and MLP) are applied to acoustic features, obtained through a procedure based on Kononenko’s discretization and correlation-based feature selection. The system encompasses five emotions (disgust, fear, happiness, anger and sadness), using the Emofilm database, comprised of short clips of English movies and the respective Italian and Spanish dubbed versions, for a total of 1115 annotated utterances. The results see MLP as the most effective classifier, with accuracies higher than 90% for single-language approaches, while the cross-language classifier still yields accuracies higher than 80%. The results show cross-gender tasks to be more difficult than those involving two languages, suggesting greater differences between emotions expressed by male versus female subjects than between different languages. Four feature domains, namely, RASTA, F0, MFCC and spectral energy, are algorithmically assessed as the most effective, refining existing literature and approaches based on standard sets. To our knowledge, this is one of the first studies encompassing cross-gender and cross-linguistic assessments on SER

Temporal limits on rubber hand illusion reflect individuals? temporal resolution in multisensory perception

Synchronous, but not asynchronous, multisensory stimulation has been successfully employed to manipulate the experience of body ownership, as in the case of the rubber hand illusion. Hence, it has been assumed that the rubber hand illusion is bound by the same temporal rules as in multisensory integration. However, empirical evidence of a direct link between the temporal limits on the rubber hand illusion and those on multisensory integration is still lacking. Here we provide the first comprehensive evidence that individual susceptibility to the rubber hand illusion depends upon the individual temporal resolution in multisensory perception, as indexed by the temporal binding window. In particular, in two studies we showed that the degree of temporal asynchrony necessary to prevent the induction of the rubber hand illusion depends upon the individuals? sensitivity to perceiving asynchrony during visuo-tactile stimulation. That is, the larger the temporal binding window, as inferred from a simultaneity judgment task, the higher the level of asynchrony tolerated in the rubber hand illusion. Our results suggest that current neurocognitive models of body ownership can be enriched with a temporal dimension. Moreover, our results suggest that the different aspects of body ownership operate over different time scales

Ultrasonic decontamination in smoked salmon experimentally contaminated with Listeria monocytogenes: Preliminary results

The purpose of this work was to evaluate the effects of ultrasound (sonication) and their combination with temperature (thermosonication) on the inactivation of Listeria monocytogenes (LM) in smoked salmon. The trial was conducted on smoked salmon samples experimentally contaminated with a cocktail of 4 strains of Listeria monocytogenes (LM ATCC 19114, LM ATCC 15313, LM ATCC 19111 and LM ATCC 7644) at a final concentration of 8 log cfu/g and kept at 4°C until its use. Thermosonication treatments between 40°C and 50°C for 5, 10 and 15 minutes proved to be more effective without altering the sensory characteristics of the food

The multi-epoch X-ray tale of I Zwicky 1 outflows

The narrow-line Seyfert 1 galaxy I Zwicky 1 shows a unique and complex system of ionised gas in outflow, which consists of an ultra-fast wind and a two-component warm absorber. In the last two decades, XMM-Newton monitored the source multiple times enabling the study of the long-term variability of the various outflows. Plasma in photoionisation equilibrium with the ionising source responds and varies accordingly to any change of the ionising luminosity. However, detailed modelling of the past RGS data has shown no correlation between the plasma ionisation state and the ionising continuum, revealing a complex long-term variability of the multi-phase warm absorber. Here, we present a new observation of I Zwicky 1 by XMM-Newton taken in early 2020 characterised by a lower X-ray flux state. The soft X-ray spectrum from the RGS reveals the two components of the warm absorber with $\log \xi \sim -1.0$ and $\log \xi \sim 1.7$. Comparing our results with the previous observations, the ionisation state of the two absorbing gas components is continuously changing, following the same unpredictable behaviour. The new results strengthen the scenario in which the ionisation state of the warm absorber is driven by the density of the gas rather than the ionising luminosity. In particular, the presence of a radiation driven, inhomogeneous clumpy outflow may explain both the variability in ionisation throughout the years and the line-locked N V system observed in the UV band. Finally, the EPIC-pn spectrum reveals an ultra-fast wind with an outflow velocity of $\sim 0.26c$ and ionisation parameter of $\log \xi \sim 3.8$.Comment: 16 pages, 11 figures, 3 tables, accepted for publication in MNRA

Time-dependent photoionization spectroscopy of the Seyfert galaxy NGC 3783

We present an investigation into the spectroscopic properties of non-equilibrium photoionization processes operating in a time-evolving mode. Through a quantitative comparison between equilibrium and time-evolving models, we find that the time-evolving model exhibits a broader distribution of charge states compared to the equilibrium model, accompanied by a slight shift in the peak ionization state depending on the source variability and gas density. The time-evolving code, tpho in SPEX, has been successfully employed to analyze the spectral properties of warm absorbers in the Seyfert galaxy NGC 3783. The incorporation of variability in the tpho model improves the fits of the time-integrated spectra, providing more accurate descriptions to the average charge states of several elements, in particular for Fe which is peaked around Fe XIX. The inferred densities and distances of the relevant X-ray absorber components are estimated to be approximately a few 1E11 per cubic meter and less than 1 pc, respectively. Furthermore, the updated fit suggests a potential scenario in which the observed absorbers are being expelled from the central AGN at the escape velocities. This implies that these absorbers might not play a significant role in the AGN feedback mechanism.Comment: accepted for publication in Astronomy and Astrophysic

Role of phytotherapy associated with antibiotic prophylaxis in female patients with recurrent urinary tract infections

Objective: Aim of this study is to evaluate the efficacy of a phytotherapic which includes Solidago, Orthosiphon and Birch extract (Cistimev®) in association with antibiotic prophylaxis in female patients affected by recurrent urinary tract infections (UTIr). Materials and methods: Patients affected by UTIr older than 18 years started a 3-months antibiotic prophylaxis (Prulifloxacin 600 mg, 1 cps/week or Phosphomicyn 1 cachet/week) according to antibiogram after urine culture. The patients were divided in 2 groups: Group A: antibiotic prophylaxis plus phytotherapy (1 cps/die for 3 months) and Group B: antibiotic prophylaxis alone. Results: 164 consecutive patients were studied: 107 were included in group A (mean age 59 ± 17.3 years) and 57 (mean age 61 ± 15.7) in group B. During the treatment period the relapse frequencies between the two groups were not significantly different (p = 0.854): 12/107 (11.21%) patients interrupted the treatment for UTIr in group A and 6/57 (10.52%) in group B. In the long term follow-up the relapse UTI risk was significant different in the two groups with a relapse risk 2.5 greater in group B than in group A (p < 0.0001). Conclusion: Our study demonstrated that in female patients affected by recurrent UTI, the association between antibiotic prophylaxis and of a phytotherapic which includes Solidago, Orthosiphon and Birch extract reduced the number of UTI in the 12 months following the end of prophylaxis and obtained a longer relapsing time, greatly improving the quality of life of the patients

Simulated microgravity promotes the formation of tridimensional cultures and stimulates pluripotency and a glycolytic metabolism in human hepatic and biliary tree stem/progenitor cells

Many pivotal biological cell processes are affected by gravity. The aim of our study was to evaluate biological and functional effects, differentiation potential and exo-metabolome profile of simulated microgravity (SMG) on human hepatic cell line (HepG2) and human biliary tree stem/progenitor cells (hBTSCs). Both hBTSCs and HepG2 were cultured in a weightless and protected environment SGM produced by the Rotary Cell Culture System (Synthecon) and control condition in normal gravity (NG). Self-replication and differentiation toward mature cells were determined by culturing hBTSCs in Kubota's Medium (KM) and in hormonally defined medium (HDM) tailored for hepatocyte differentiation. The effects on the expression and cell exo-metabolome profiles of SMG versus NG cultures were analyzed. SMG promotes tridimensional (3D) cultures of hBTSCs and HepG2. Significative increase of stemness gene expression (p < 0.05) has been observed in hBTSCs cultured in SMG when compared to NG condition. At the same time, the expression of hepatocyte lineage markers in hBTSCs differentiated by HDM was significantly lower (p < 0.05) in SMG compared to NG, demonstrating an impaired capability of hBTSCs to differentiate in vitro toward mature hepatocytes when cultured in SMG condition. Furthermore, in HepG2 cells the SMG caused a lower (p < 0.05 vs controls) transcription of CYP3A4, a marker of late-stage (i.e. Zone 3) hepatocytes. Exo-metabolome NMR-analysis showed that both cell cultures consumed a higher amount of glucose and lower glutamate in SMG respect to NG (p < 0.05). Moreover, hBTSCs media cultures resulted richer of released fermentation (lactate, acetate) and ketogenesis products (B-hydroxybutyrate) in SGM (p < 0.05) than NG. While, HepG2 cells showed higher consumption of amino acids and release of ketoacids (3-Methyl-2-oxovalerate, 2-oxo-4-methyl-valerate) and formiate with respect to normogravity condition (p < 0.05). Based on our results, SMG could be helpful for developing hBTSCs-derived liver devices. In conclusion, SMG favored the formation of hBTSCs and HepG2 3D cultures and the maintenance of stemness contrasting cell differentiation; these effects being associated with stimulation of glycolytic metabolism. Interestingly, the impact of SMG on stem cell biology should be taken into consideration for workers involved in space medicine programs