Determination of the best empiric method to quantify the amplified spontaneous emission threshold in polymeric active waveguides

Amplified Spontaneous Emission (ASE) threshold represents a crucial parameter often used to establish if a material is a good candidate for applications to lasers. Even if the ASE properties of conjugated polymers have been widely investigated, the specific literature is characterized by several methods to determine the ASE threshold, making comparison among the obtained values impossible. We quantitatively compare 9 different methods employed in literature to determine the ASE threshold, in order to find out the best candidate to determine the most accurate estimate of it. The experiment has been performed on thin films of an homopolymer, a copolymer and a host:guest polymer blend, namely poly(9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-cobenzothiadiazole) (F8BT) and F8BT:poly(3- hexylthiophene) (F8BT:rrP3HT), applying the Variable Pump Intensity (VPI) and the Variable Stripe Length (VSL) methods. We demonstrate that, among all the spectral features affected by the presence of ASE, the most sensitive is the spectral linewidth and that the best way to estimate the ASE threshold is to determine the excitation density at the beginning of the line narrowing. We also show that the methods most frequently used in literature always overestimate the threshold up to more than one order of magnitude

Soft Body Impact Against Aeronautical Structures

Statistics show that impacts of soft body against aeronautical structure are not so rare events. The damage caused by the impact of hailstones or of birds can sometimes be so heavy to compromise the service life of the vehicle. Companies, research centers and universities are interested in the evaluation of the effects of this kind of events and lots of researching works have been recently developed in this field. In this paper, an overview of the last studies performed at the Laboratory for the Safety in Transports (LaST – Crash Lab.) of Politecnico of Milan are presented throughout experimental tests and numerical finite element models. The validity of the correlation results method to prevent possible heavy consequence caused by these events is shown

Approximating Spectral Impact of Structural Perturbations in Large Networks

Determining the effect of structural perturbations on the eigenvalue spectra of networks is an important problem because the spectra characterize not only their topological structures, but also their dynamical behavior, such as synchronization and cascading processes on networks. Here we develop a theory for estimating the change of the largest eigenvalue of the adjacency matrix or the extreme eigenvalues of the graph Laplacian when small but arbitrary set of links are added or removed from the network. We demonstrate the effectiveness of our approximation schemes using both real and artificial networks, showing in particular that we can accurately obtain the spectral ranking of small subgraphs. We also propose a local iterative scheme which computes the relative ranking of a subgraph using only the connectivity information of its neighbors within a few links. Our results may not only contribute to our theoretical understanding of dynamical processes on networks, but also lead to practical applications in ranking subgraphs of real complex networks.Comment: 9 pages, 3 figures, 2 table

WILSON PLOT METHOD TO OBTAIN NUSSELT NUMBER FOR A PLATE HEAT EXCHANGER

Plate heat exchangers are devices commonly used in industry due to their high efficiency and ease cleaning. Although its first use was in food sector, nowadays this equipment can be found in most industrial segments, like chemistry and oil industry. Due the facility of fabrication, the corrugated gasket plate heat exchanger is amply utilized in those segments, however, its mathematical analysis present non-agreement between the authors, because of the different plate models and operation settings. Thus, the main objective of this work is to study the application of the Wilson-Plot method to analyze the thermal behavior of an elemental plate heat exchanger, and verify if the operation temperature has significant influence in the thermal behavior of the plate heat exchanger

Development of a novel CO2splitting fixed-bed reactor based on copper-doped cerium oxide

Global warming has received widespread attention in recent years due to the accumulation of carbon dioxide. Looking at the current energy landscape, new technologies must be developed to reduce CO2 emissions. The present work is aimed to develop and test a new prototype of an innovative reactor for the conversion of CO2 into CO, operating according to a two-phase thermochemical cycle. The innovative and main aspect of this study was the use of a reactor coupled with a new type of catalyst, a copper-doped cerium oxide (Cuδ+2Ce(1-δ)O2), which allowed to decrease the temperature of the reaction up to 850°C, much lower than the models present in the literature, tested on 1300/1400°C and even beyond

Posterior arch defect of the atlas associated to absence of costal element of foramen transversarium from 16th century Sardinia (Italy)

Study Design. A paleopathological case of posterior arch defect of the atlas associated to the absence of costal element of the foramen transversarium. Objective. In living patients as well as in postmortem analysis it should be difficult to distinguish between a congenital and an acquired anomaly. Any anomaly in the anatomy of atlas should be taken into consideration by clinicians, surgeons, radiologists, and anatomists in order to avoid misinterpretations and clinical complications. Summary of Background Data. Posterior arch defect has a current occurrence of approximately 4%. Posterior arch schisis is attributed to the defective or absent development of the cartilaginous preformation of the arch rather than a disturbance of the ossification. The absence of costal element of the foramen transversarium has an incidence of ranging from 2% to 10% and is attributed to a developmental defect or to variations in the course of the vertebral artery. Methods. The skeleton of a man aged 20–30 years, brought to light in the plague cemetery of 16th century Alghero (Sardinia), showed anomalies of the atlas, consisting in failure of the midline fusion of the 2 hemiarches with a small gap and an open anterior foramen trasversarium on the left side. A macroscopic, radiological, and stereomicroscopic study was carried out. Results. The study allowed to rule out a traumatic origin of the defects and to diagnose an association of 2 congenital anomalies. Conclusion. Osteoarchaeological cases provides with a valuable opportunity to examine and describe variations in the anatomy of the atlas

evaluation of botulinum toxin therapy of spastic equinus in paediatric patients with cerebral palsy

Objective: To develop a clinical and instrumental protocol to assess the postural and dynamic effects following treatment with botulinum neurotoxin A in children with cerebral palsy affected by spastic equinus. Design: Open study, in which every patient served as his or her own control. Patients: Ten sequential children with cerebral palsy and spastic dynamic equinus foot. Methods: Botulinum neurotoxin A was injected in the gastrocnemius, soleus and tibialis posterior muscles. The main measures were: pedobarometry, dynamic surface electromyography, video gait analysis scale, and the modified As hworth Scale. Results: After treatment with botulinum neurotoxin A, pedobarometric evaluation revealed a significant change in all parameters, including a decrease in the modified Ashworth Scale and an increase in the range of motion. All children showed significant improvement in initial foot contact, as documented by the video gait analysis scale. The calf muscle electromyography pattern showed a decrease in co-contraction during gait in all children. These modifications were sta tistically significant for all parameters considered ( p < 0.05). Conclusion: This pilot study suggests that dynamic electr

A Two-dimensional Numerical Study of Ion-Acoustic Turbulence

We investigate the linear and nonlinear evolution of the ion-acoustic instability in a collisionless plasma via two-dimensional (2D2V) Vlasov-Poisson numerical simulations. We initialize the system in a stable state and gradually drive it towards instability with an imposed, weak external electric field, thus avoiding super-critical initial conditions that are physically unrealizable. The nonlinear evolution of ion-acoustic turbulence (IAT) is characterized in detail, including the particles' distribution functions, particle heating, (two-dimensional) wave spectrum, and the resulting anomalous resistivity. An important result is that no steady saturated nonlinear state is ever reached in our simulations: strong ion heating suppresses the instability, which implies that the anomalous resistivity associated with IAT is transient and short-lived. Electron-acoustic waves (EAWs) are triggered during the late nonlinear evolution of the system, caused by strong modifications to the particle distribution induced by IAT