192 research outputs found
Superconduttivita: analisi fenomenologica e termodinamica
In questo lavoro di tesi si vanno a studiare e descrivere le proprietà dei superconduttori,
le principali osservazioni sperimentali e si espongono le più importanti
equazioni fenomenologiche sviluppate a partire da una trattazione basata sulle
proprietà elettriche, magnetiche e termodinamiche dei superconduttori.
Nel capitolo 1 vengono esposte le evidenze sperimentali più importanti di
cui bisogna tenere conto per sviluppare una teoria che descriva correttamente i
superconduttori.
Nel capitolo 2 si ricavano le principali relazioni termodinamiche che riguardano
le transizioni di fase dei superconduttori, utilizzando B, H e T come parametri
termodinamici.
Nella prima parte del capitolo 3 si espone il modello di London per la superconduttività ,
si ricavano le omonime equazioni e si risolvono in alcuni casi semplici,
inoltre si discutono le leggi di conservazione che le equazioni di London implicano.
Nella seconda parte si procede alla descrizione dell’equazione di Pippard che
corregge alcune previsioni errate che emergono utilizzando le equazioni di London.
Nel capitolo 4 viene descritta la teoria fenomenologica proposta da Ginzburg
e Landau basata sulle transizioni di fase del secondo ordine; si espone la teoria
per sistemi omogenei e non, e sistemi immersi in campo magnetico, vengono ricavate
le equazioni che permettono di descrivere alcune importanti proprietà dei
superconduttori e che ne permettono la classificazione in tipo I o II a seconda del
comportamento in risposta all’applicazione di un campo magnetico esterno
Identification of C-band radio frequency interferences from Sentinel-1 data
We propose the use of Sentinel-1 Synthetic Aperture Radar (SAR) to provide a continuous and global monitoring of Radio Frequency Interferences (RFI) in C-band. We take advantage of the first 8-10 echo measures at the beginning of each burst, a 50-70 MHz wide bandwidth and a ground beam coverage of ~25 km (azimuth) by 70 km (range). Such observations can be repeated with a frequency better than three days, by considering two satellites and both ascending and descending passes. These measures can be used to qualify the same Sentinel-1 (S1) dataset as well as to monitor the availability and the use of radio frequency spectrum for present and future spaceborne imagers and for policy makers. In the paper we investigate the feasibility and the limits of this approach, and we provide a first Radio Frequency Interference (RFI) map with continental coverage over Europe
Impact of scene decorrelation on geosynchronous SAR data focusing
We discuss the effects of the clutter on geosynchronous SAR systems exploiting long integration times (from minutes to hours) to counteract for two-way propagation losses and increase azimuth resolution. Only stable targets will be correctly focused whereas unstable targets will spread their energy along azimuth direction. We derive here a generic model for the spreading of the clutter energy based on the power spectral density of the clutter itself. We then assume the Billingsley Intrinsic Clutter Motion model, representing the clutter power spectrum as an exponential decay, and derive the expected GEOSAR signal-to-clutter ratio. We also provide some results from a Ground Based RADAR experiment aimed at assessing the long-term clutter statistics for different scenarios to complement the Internal Clutter Motion model, mainly derived for windblown trees. Finally, we discuss the expected performances of two GEOSAR systems with different acquisition geometries.Peer ReviewedPostprint (published version
Geosynchronous SAR for Terrain & atmosphere with short revisit (GeoSTARe)
Geo STA Re would be a mission combining the continuous view capabilities from geostationary orbits of super-continental areas with the all-day, all-weather imaging capabilities of Synthetic Aperture Radar. It would complement Copernicus Sentinel-1 bringing the repeat time from days down to hours. In that, it would provide novel and unique observations. The well proven potentials of Radar in sensing roughness, deformations, and moisture, combined with the short time to get any image, from minutes to an hour, and the immediate data download and exploitation (thanks to the geostationary orbit) makes GeoSTARe a game changer in those fields where hourly-to-daily monitoring is a must
Site-specific integration in mammalian cells mediated by a new hybrid baculovirus-adeno-associated virus vector
Baculovirus can transiently transduce primary human and rat hepatocytes, as well as a subset of stable celllines. To prolong transgene expression, we have developed new hybrid vectors which associate key elementsfrom adeno-associated virus (AAV) with the elevated transducing capacity of baculovirus. The hybrid vectorscontain a transgene cassette composed of the !-galactosidase (!-Gal) reporter gene and the hygromycin resistance(Hygr) gene flanked by the AAV inverted terminal repeats (ITRs), which are necessary for AAV replicationand integration in the host genome. Constructs were derived both with and without the AAV rep geneunder the p5 and p19 promoters cloned in different positions with respect to the baculovirus polyheidrinpromoter. A high-titer preparation of baculovirus-AAV (Bac-AAV) chimeric virus containing the ITR–Hygr–!-Gal sequence was obtained with insect cells only when the rep gene was placed in an antisense orientationto the polyheidrin promoter. Infection of 293 cells with Bac-AAV virus expressing the rep gene results in a 10-to 50-fold increase in the number of Hygr stable cell clones. Additionally, rep expression determined the localizationof the transgene cassette in the aavs1 site in approximately 41% of cases as detected by bothSouthern blotting and fluorescent in situ hybridization analysis. Moreover, site-specific integration of the ITRflankedDNA was also detected by PCR amplification of the ITR-aavs1 junction in transduced human fibroblasts.These data indicate that Bac-AAV hybrid vectors can allow permanent, nontoxic gene delivery of DNAconstructs for ex vivo treatment of primary human cells
The Evaluation of the Detection of Cr(VI) in Leather
The topic of hexavalent chromium (Cr(VI)) in leather has been debated throughout the whole supply chain for years. However, its significance has recently increased due to proposed changes in European legislation concerned with skin-sensitising substances suggesting that acceptable Cr(VI) concentrations in leather goods should be lowered from 3 mg kg 121 to 1 mg kg 121. The proposition of a stricter limit and current analytical difficulties created the need for a review of current standard test methods. The research presented in this paper investigates both the colorimetric (Part 1) and chromatographic (Part 2) methods under BS EN ISO 17075. The focus of the study was to identify possible sources of interference leading to large statistical variance in results and to define the limit of quantification with respect to the proposed new compliance limit. This study into the colorimetric method has shown that the presence of Cr(III), dyes, and proteins can be significant interferences, becoming critical at low Cr(VI) concentrations. Dilution factors worsen the problem of detecting low concentrations: a reliable quantitative detection of 0.01 mg kg 121 and 0.003 mg kg 121 Cr(VI) in solution are required at the 3 mg kg 121 and 1 mg kg 121 compliance limits in leather, respectively. BS EN ISO 17075 part 1 was shown to be incapable of reliably resolving to 3 mg kg 121 or below in leather. Part 2 shows a marked improvement in detection limits and reliability; however, data suggest that 1 mg kg 121 Cr(VI) is not reliably detectable in leather. Suggested improvements to the established test methods and a possible alternative are discussed
Excitonic effects in energy loss spectra of freestanding graphene
In this work we perform electron energy-loss spectroscopy (EELS) of
freestanding graphene with high energy and momentum resolution to disentangle
the quasielastic scattering from the excitation gap of Dirac electrons close to
the optical limit. We show the importance of many-body effects on electronic
excitations at finite transferred momentum by comparing measured EELS with ab
initio calculations at increasing levels of theory. Quasi-particle corrections
and excitonic effects are addressed within the GW approximation and
Bethe-Salpeter equation, respectively. Both effects are essential in the
description of the EEL spectra to obtain a quantitative agreement with
experiments, with the position, dispersion, and shape of both the excitation
gap and the plasmon being significantly affected by excitonic effects
Prevalence and time course of post-stroke pain: A multicenter prospective hospital-based study
OBJECTIVE:
Pain prevalence data for patients at various stages after stroke.
DESIGN:
Repeated cross-sectional, observational epidemiological study.
SETTING:
Hospital-based multicenter study.
SUBJECTS:
Four hundred forty-three prospectively enrolled stroke survivors.
METHODS:
All patients underwent bedside clinical examination. The different types of post-stroke pain (central post-stroke pain, musculoskeletal pains, shoulder pain, spasticity-related pain, and headache) were diagnosed with widely accepted criteria during the acute, subacute, and chronic stroke stages. Differences among the three stages were analyzed with χ(2)-tests.
RESULTS:
The mean overall prevalence of pain was 29.56% (14.06% in the acute, 42.73% in the subacute, and 31.90% in the chronic post-stroke stage). Time course differed significantly according to the various pain types (P < 0.001). The prevalence of musculoskeletal and shoulder pain was higher in the subacute and chronic than in the acute stages after stroke; the prevalence of spasticity-related pain peaked in the chronic stage. Conversely, headache manifested in the acute post-stroke stage. The prevalence of central post-stroke pain was higher in the subacute and chronic than in the acute post-stroke stage. Fewer than 25% of the patients with central post-stroke pain received drug treatment.
CONCLUSIONS:
Pain after stroke is more frequent in the subacute and chronic phase than in the acute phase, but it is still largely undertreated
An Intraoperative Detecting Probe For Radio-Guided Surgery in Tumour Resection
The development of the based radio-guided surgery aims to extend
the technique to those tumours where surgery is the only possible treatment and
the assessment of the resection would most profit from the low background
around the lesion, as for brain tumours. Feasibility studies on meningioma,
glioma, and neuroendocrine tumors already estimated the potentiality of this
new treatment. To validate the technique, prototypes of the intraoperative
probe required by the technique to detect radiation have been
developed. This paper discusses the design details of the device and the tests
performed in laboratory. In such tests particular care has to be taken to
reproduce the surgical field conditions. The innovative technique to produce
specific phantoms and the dedicated testing protocols is described in detail.Comment: 7 pages, 15 figure
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