193 research outputs found
The Tetragonal to Orthorhombic structural phase transition in multiband FeAs-based superconductors
We report the temperature dependent x-ray powder diffraction of the
FeAs-based superconductors in the range between 300 K and 95 K. In the case of
NdOFeAs we have detected the structural phase transition from the tetragonal
phase, with P4/nmm space group, to the orthorhombic phase,with Cmma space
group, over a broad temperature range from 150 K to 120 K, centered at T0 137K.
This transition is reduced, by about 30K, by the internal chemical pressure
going from LaOFeAs to NdOFeAs. On the contrary the superconducting critical
temperature increases from 27K to 51 K going from LaOFeAs to NdOFeAs doped
samples. The FeAs layers in all undoped 1111 and 122 systems suffer a tensile
misfit strain. The tensile misfit strain is reduced in 1111 and in 122 samples
and at optimum doping the misfit strain is close to zero. This result shows
that the normal striped orthorhombic Cmma phase competes with the
superconducting tetragonal phase. In the orthorhombic clusters the charges can
move only along the stripes in the b direction and are localized by the
magnetic interaction.Comment: 9 pages and 2 figures. accepted by Journal of Superconductivity and
novel magnetis
The Microstrain-Doping Phase Diagram of the Iron Pnictides Heterostructures at Atomic Limit
The 3D phase diagram of iron pnictides where the critical temperature depends
on charge density and microstrain in the active FeAs layers is proposed. The
iron pnictides superconductors are shown to be a practical realization of a
heterostructure at the atomic limit made of a superlattice of FeAs layers
intercalated by spacer layers. We have focussed our interest on the A 1-x
BxFe2As2 (122) families and we show that FeAs layers have a tensile microstrain
due to the misfit strain between the active layers and the spacers. We have
identified the critical range of doping and microstrain where the critical
temperature gets amplified to its maximum value.Comment: 5 pages, 3 figure
A model for liquid-striped liquid phase separation in liquids of anisotropic polarons
The phase separation between a striped polaron liquid at the particular
density and a high density polaron liquid is described by a modified Van der
Waals scheme. The striped polaron liquid represents the pseudo gap matter or
Wigner-like polaron phase at 1/8 doping in cuprate superconductors. The model
includes the tendency of pseudo- Jahn-Teller polarons to form anisotropic
directional bonds at a preferential volume with the formation of different
liquid phases. The model gives the coexistence of a first low density polaron
striped liquid and a second high density liquid that appears in cuprate
superconductors for doping larger than 1/8. We discuss how the strength of
anisotropic bonds controls the variation the phase separation scenarios for
complex systems in the presence of a quantum critical point where the phase
separation vanishes.Comment: 10 pages, 3 figure
Design Of Experiments for the optimization the process parameters of thixotropic aluminum alloy
The success of the thixoforming process depends on the possibility to confer to material, when it is found in the semisolid state, a microstructure characterized by globular particles of solid phase surrounded by a continuous film of liquid phase; such microstructure is obtainable through particular thermo-mechanical treatments. In the present research, in order to optimize the influence of process parameters in the step in which the thixotropic properties are conferred to the AA7075 aluminum alloy, the statistic technique of the Design Of Experiments (DOE) has been used. The advantages in the application of such technique are expressible in terms of reduction the times of development of process and more efficient use of resources. A Central Composite Design factorial plan with two levels has been realized to allow the evaluation of experimental error and to check the adequacy of the model. The experimental tests foreseen from the same plan have been therefore performed. Using the method of the response surfaces (RSM), the function of response has been formulated, and the analysis of the experimental data has been realized by the linear regression method. Finally, the analysis of variance (ANOVA) allowed to value the causes of variability of the results. Statistic test has been performed on the significance of single factors and their interactions
Health Technology Assessment: An Essential Approach to Guide Clinical Governance Choices on Risk Management
A large part of academic literature, business literature as well as practices in real life are resting on the assumption that uncertainty and risk does not exist. We all know that this is not true, yet, a whole variety of methods, tools and practices are not attuned to the fact that the future is uncertain and that risks are all around us. However, despite risk management entering the agenda some decades ago, it has introduced risks on its own as illustrated by the financial crisis. Here is a book that goes beyond risk management as it is today and tries to discuss what needs to be improved further. The book also offers some cases
Strumenti di analisi e simulazione applicati al management sanitario: procedure di parto a confronto
Le politiche sanitarie attuali impongono livelli di assistenza di eccellenza ed un taglio immediato e consistente alla spesa. Tutto ciò, nonostante una produca nel breve periodo una maggiore compliance rispetto ai parametri finanziari individuati, può pericolosamente generare costi di lungo periodo sul sistema stesso e soprattutto per la necessità di agire con interventi immediati ma generalisti.
La programmazione delle risorse rappresenta una delle possibili soluzioni per il contenimento di una spesa, che per ragioni demografiche ed ambientali, continua a crescere anno dopo anno. Tuttavia la capacità di analizzare, soprattutto nel lungo periodo, le ripercussioni di azioni specifiche è fortemente limitata dalle condizioni di deficit nazionale e difficilmente estesa all’impatto che tutti i servizi offerti dal sistema sanitario nazionale producono.
Ad oggi la spesa sanitaria è analizzata principalmente attraverso le serie storiche, cioè mediante la valutazione delle risorse impiegate negli anni precedenti, e raramente attraverso l’analisi delle proiezioni di spesa che possono derivare dalle procedure sanitarie stesse. In questo ambito gli strumenti di analisi ed i modelli previsionali possono fornire un aiuto importante nella stima dei budget.
La programmazione delle risorse inoltre deve tenere conto di fattori sociali e demografici ed in particolare seguire il processo di valutazione multifattoriale necessario per tutte le tecnologie sanitarie (HTA).
Questo lavoro si pone l'obiettivo di esplorare il possibile utilizzo di metodologie proprie del management aziendale e delle scienze socio-economiche all’ambito sanitario.
In particolare, nel corso di questa tesi sono mostrate applicazioni pratiche del clustering gerarchico tramite la tecnica dell’Analytic Hierarchy Process (AHP), e del System Thinking. Le applicazioni hanno avuto come tema dominante il confronto tra le due principali procedure alternative di parto: il parto vaginale e quello con taglio cesareo
Royal Jelly: An ancient remedy with remarkable antibacterial properties
Royal Jelly (RJ), a honeybee hypopharyngeal gland secretion of young nurse and an exclusive nourishment for bee queen, has been used since ancient times for care and human health and it is still very important in traditional and folkloristic medicine, especially in Asia within the apitherapy. Recently, RJ and its protein and lipid components have been subjected to several investigations on their antimicrobial activity due to extensive traditional uses and for a future application in medicine. Antimicrobial activities of crude Royal Jelly, Royalisin, 10-hydroxy-2-decenoic acid, Jelleines, Major Royal Jelly Proteins against different bacteria have been reported. All these beehive products showed antimicrobial activities that lead their potential employment in several fields as natural additives. RJ and its derived compounds show a highest activity especially against Gram positive bacteria. The purpose of this Review is to summarize the results of antimicrobial studies of Royal Jelly following the timescale of the researches. From the first scientific applications to the isolation of the single components in order to better understand its application in the past years and propose an employment in future studies as a natural antimicrobial agent
Beeswax: A minireview of its antimicrobial activity and its application in medicine
Abstract Beeswax is the substance that forms the structure of a honeycomb; the bees secrete wax to build the honeycombs where to store honey. Thanks to its rich hydrophobic protective properties, the beeswax is in fact present within cosmetics and body products. Also, beeswax is used in the food industry: as a film to wrap cheese for maturing or as a food additive (E901) to give shine to the products. Exactly as the honey which it contains, beeswax is also characterized by several therapeutic properties of great interest to us; it is thought to be particularly effective in healing bruises, inflammation and burns. Recently, the interest of researchers has moved even on antimicrobial properties of beeswax although there are still few studies in the literature focused only on the action of beeswax. The few studies showed an antimicrobic effectiveness of beeswax against overall Staphylococcus aureus , Salmonella enterica , Candida albicans and Aspergillus niger ; these inhibitory effects are enhanced synergistically with other natural products such as honey or olive oil. This minireview aims to be a collection of major scientific works that have considered the antimicrobial activity of beeswax alone or in combination with other natural products in recent years
Electromyography in the Study of Muscle Reactions to Vibration Treatment
Electromyography (EMG) is a common used technique to evaluate muscular activity.
Analysis of EMG recordings is important for assessing muscle activation, its relationship to the force developed during specific tasks and for evaluating fatigue processes occurring in response to physical activity.
Electromyography can be performed using different types of electrodes, depending on the specific analysis: surface (or skin) electrodes or inserted electrodes (wire and needle); the first it is used to monitor the overall activity of a muscle while the second is generally used to reveal the electrical activity of a nerve root. (De Luca, 1997, Basmajan and De Luca, 1985)
Electrode types and configurations, as well as associated instrumentation, influence the quality of the EMG signal detected and displayed, recorded or processed (Merletti et al, 2001; Saitou et al, 2000; Rainoldi et al, 2004, Nishihara et al, 2008). Various studies have been dedicated to the matter and guidelines in EMG recording are available (Basmajan and De Luca, 1985, Hermens H.J. et al, 1999).
Surface electromyography (SEMG) analysis is a largely used EMG recording method as it is non–invasive, safe, it does not cause pain and it is simple to perform. Root mean square (RMS) of the surface EMG signals is often used as a concise quantitative index of muscle
activity; indeed, electromyography devices often provide EMG RMS output.
SEMG is often used for the assessment of muscle activity occurring in response to physiological or to externally applied stimuli, i.e. vibratory stimulation.
Vibration stimulus is a mechanical muscle excitation, applied generally to a tendon, a muscle or to the body as a whole, aimed to activate muscles by eliciting stretch reflexes.
Local tendon vibrations induce activiy of the muscle spindle Ia fibers, mediated by monosynaptic and/or polysynaptic pathways; the reflex muscle contraction that arises in response to such vibratory stimulus has been named Tonic Vibration Reflex (TVR). (Roll et al, 1989; Bongiovanni and Hagbart, 1990; Romaiguére et al, 1991; Person and Kozhina, 1992; Martin and Park, 1997)
As well as in other external stimulation, vibratory muscle activation can be examined by the analysis of electromyography recordings. Many studies report a significant increase of EMG RMS values in the lower body muscles during vibration training, these changes suggested
an increase in neuromuscular activity (Cardinale and Bosco, 2003; Verschueren et al, 2004).
Specific WBV frequencies seem to produce a higher EMG RMS signal than others (Cardinale and Lim 2003). However, as well as in every surface bio-potential recording, during local or whole body vibration treatment the EMG signal can be affected by artifacts.
Motion artifacts may in fact arise from relative motion between electrodes and skin and also between skin layers. The only skin stretch may result in a variation of electrode potential (Turker, 1993, De Talhouet and Webster, 1996; Ă–dman and Ă–berg, 1982, Searle and Kirkup, 2000, Tam and Webster, 1977).
In classical clinical EMG recordings (isokinetic, isotonic, gait, etc.), frequency content of motion artifact is considered below 10-20 Hz, then the general approach to motion artifact reduction is to apply a high-pass filter (e.g. with a cut-off frequency of 20 Hz).
During vibratory stimulation the artifact frequency contents, typically limited at vibratory frequency and its har onics, extend within the EMG spectrum (Fratini et al, 2009) and standard high-pass filters are not suitable for filtering out this artifact.
In the majority of the cases appropriate filtering is used to remove motion artifacts before any signal analysis, while in some other they are used to characterize the mechanical response of the tissue to a specific stimulus (mechanogram) and its correlation to the
stimulus itself (Person and Kozhina, 1992; Fratini et al, 2009).
With this chapter the authors aim to investigate the use and the efficacy of surface electromyography in the study of muscle response to vibration treatments. A review ofvibration characterization and analysis is reported, SEMG recordings of Rectus Femori, Vastus Medialis and Vastus Lateralis were collected and analyzed.
Specific artifacts were revealed and the role of those artifact was investigated and assessed.
Since the use of vibratory stimulus produces peculiar EMG response a specific model was adopted to describe the EMG synchronization effect and its influence on the resultant recorded muscle activity (Person and Kozhina, 1992)
Friction Stir Welding of Ti6Al4V complex geometries for aeronautical applications: a feasibility study
While Friction Stir Welding (FSW) of aluminium alloys can be considered a mature technology, even for complex joint morphologies, as T joints welded “in transparency”, welding of hard material still presents several open issues. In fact, welding of titanium alloys is a challenging process due to the chemical, mechanical and thermal characteristics of such materials which are subjected to atmosphere contamination resulting in joint hydrogen, oxygen and nitrogen embrittlement; additionally, due to the high melting temperature, large distortion and residual stress are found in joints obtained by traditional fusion welding processes as gas metal arc welding, electron beam welding and laser welding. In this way a solid-state process, as FSW, represents a valid choice in order to overcome problems related to the material melting. It should be noticed that FSW of titanium alloys is definitely more complex than the same process referred to aluminium alloys. In the proposed paper, a feasibility study on the production of Ti6Al4V T-joints in one welding pass, i.e. the so-called transparency welding, is presented. The main process parameters, i.e. tool rotation and feed rate have been fixed, and the main metallurgical and mechanical properties of the joint have been analysed. Macro and micro observations of the joints have been performed relating the final microstructure to the input process parameters utilized
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