1,721,133 research outputs found
Intensity and fluctuation dynamics in pump-probe experiments in complex materials
No full textThe work presented in this thesis is focused on out-of-equilibrium experiments on strongly correlated systems, both with ``standard'' pump-probe spectroscopy and time resolved single pulse statistics. We applied these techniques mainly on a High Temperature Superconductor, an optimally doped Bi2 Sr2 Y0.08 Ca0.92 Cu2 O(8+x) (Y-Bi2212). These materials show intriguing and still unexplained properties, such as the presence of the pseudogap phase.
The aim of the first part of the thesis is to analyze the phase transition between superconducting and pseudogap phases, through the combination of time resolved techniques, suitable for the study of strongly correlated systems, and electronic Raman spectroscopy, which allows to detect anisotropic behaviors in the reciprocal space. The experimental result was a map of the de-excitation dynamics as a function of temperature across Tc The excitation was provided by mid-infrared pulses at two different photon energies (above and below the superconducting gap) and polarizations. The results show that a low photon energy pump polarized along the Cu-Cu direction causes a larger dynamical superconducting response with respect to the Cu-O polarized excitation, both below and above the critical temperature. The results are supported by an effective theoretical model based on BCS theory for a superconductor with an anisotropic d-wave gap typical of cuprates. The model reveals a dynamical enhancement of the superconducting order parameter for a Cu-Cu polarized pump, which is due to the increase of phase coherence of the pair operator, whereas the density of Cooper pairs seems not to be strongly affected by the excitation.
In the second part of the thesis we wanted to move a step forward and to study the statistical distribution of the probe pulses. The intrinsic noise of the photon number distribution reveals a completely distinct behavior in the various phases of the sample: it follows the mean photon number dynamics in the metallic states, whereas it has a different time resolved signal (and in particular the noise has a longer time decay) in the superconducting state. A simple quantum model, which describes the dissipative processes of the set-up as perfect beam splitters, has been implemented to simulate the observed peculiar results. From the model it turns out that the non-selected polarization contributes to the final noise signal, giving rise to a completely different dynamics for high and low temperatures. This interpretation shows how, whereas it is always possible to select photons with certain features (such as polarization) in ``standard'' intensity measurements, footprints of every interaction are kept in the noise
Reproducibility of atopy patch tests with Dermatophagoides: a study on 85 patients with atopic dermatitis
No full textAtopy patch tests (APTs) are considered a useful addition to standard testing procedures for the identification of allergens triggering the appearance of eczema in patients with atopic dermatitis (AD). The aim of the study was to evaluate the reproducibility of APTs with house dust mites by simultaneously patch testing AD patients. 85 subjects affected by AD, 36 males and 48 females, aged from I to 52 years, were patch tested with Dermatophagoides mix (D. pteron/D.farinae) 20% pet. In our patients, the percentage of agreement between the frequency of positive and negative responses to Dermatophagoides mix was 96.7%. Reproducibility was highly satisfactory, as evaluated by k-value (0.953). As regards the agreement in the intensity of APT responses to Dermatophagoides mix between the right and left sides, we found that reproducibility was also highly satisfactory (k = 0.851). In conclusion, for Dermatophagoides APTs, the agreement rate was similar to that of standard patch tests, and therefore APTs may be considered sufficiently reproducible to be employed as a diagnostic testing procedure
Food atopy patch test and repeated food challenge
No full textFood hypersensitivity is a common medical problem in atopic dermatitis (AD) patients, mainly in paediatric age. Patch tests based on prolonged exposure of the skin to food, aiming at the detection of delayed reactions, represent a testing modality reproducing skin responses against allergens normally occurring in AD. Atopy patch tests (APTs) have been demonstrated to improve the accuracy of skin testing in the diagnosis of food allergy in AD patients; whereas immediate-type reactions proved to be associated with skin prick test positivity, APT reactivity is more frequently observed in patients with delayed responses. Relevance of positive and negative APT responses should be assessed by food challenge results. Double-blind placebo-controlled food challenge (DBPCFC) is considered the gold standard for diagnosing food allergy, however, besides the fact that there is no universally accepted standard for performing the DBPCFC, these testing and observation modalities may not identify the whole spectrum of skin reactions possibly appearing in AD patients after food ingestion, which encompasses both prompt and eczematous responses sometimes appearing more than 48 hours after the challenge and requiring repeated administration of the foodstuff. Since many authors demonstrated that an open challenge associated to careful follow-up can prove adequate in identifying food allergic patients, also enabling the diagnosis of delayed reactions, the repeated open food challenge (ROFC) may be considered a useful and practical alternative to DBPCFCs. In our experience this challenge modality seems to be well accepted and enables a good compliance. The subjects undergoing challenge are given a dose of the suspected food reflecting the normal intake daily at home for a week. The first administration is performed at the hospital in selected cases, depending on the nature and severity of the reaction to food allergens. When a clinical reaction is noted, the test is stopped and the patient is examined at the hospital. All subjects are examined on day 7 of the challenge. APTs with egg, cow’s milk and peanut were performed in 222 AD subjects undergoing repeated open challenges. 11%, 9% and 22% of them reacted to APT with egg, milk and peanut, respectively. Whereas sensitivity figures were low (31% for egg, 15% for cow’s milk, and 37% for peanut), specificity was high (79% for egg, 92% for cow’s milk, and 77% for peanut), indicating that a positive patch test enables the identification of food-allergic subjects
Alternaria alternata patch tests on a study population of 500 atopic dermatitis patients
No full textIntroduction: Literature data on clinical symptoms related to exposure to Alternaria Alternata mostly concern subjects with respiratory atopy, whereas its role in the pathogenesis of atopic dermatitis (AD) has been poorly investigated. The aim of this study was to investigate Alternaria Alternata patch test results and to correlate the results to clinical history and specific IgE.Methods: 500 patients with atopic dermatitis (AD), 222 males and 278 females, underwent patch testing with Alternaria Alternata 2.4% in petrolatum, provided by Lofarma (Milano, Italy). Specific IgE to Alternaria Alternata were detected by prick tests (Stallergenes, France).Results: 38 (7,6%) patients, 13 males and 25 females, proved positive to Alternaria Alternata patch test. Among them, 12 subjects were affected by rhinitis and/or asthma. The most frequently involved skin sites in AD patients sensitised to Alternaria Alternata were the face, the flexural areas of the limbs and the neck. Among patients undergoing skin testing, 64 (12,8%) reacted to Alternaria Alternata prick tests. Discussion: The significance of positive patch test responses to Alternaria Alternata patch tests remains questionable. The possibility that molds may be involved in the development of skin lesions in patch test-positive AD patients, should be checked with specific provocation and elimination procedures, which is particularly difficult, owing to the multifactorial etiology of AD
Coloranti dispersi : frequenza e caratteristiche della sensibilizzazione allergica da contatto.
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