196,071 research outputs found
Design and operation of a femtosecond micro-CARS experimental apparatus
Full text linkLa spettroscopia Raman consente di misurare mappe vibrazionali di campioni con alta risoluzione spaziale, utili per l’identificazione di composti chimici senza l’utilizzo di marcatori. In generale però, le tecniche di Raman spontaneo soffrono di alcuni svantaggi, principalmente dovuti ai bassi livelli di segnale e alla eventuale presenza di segnali di fluorescenza, che possono limitarne l’applicabilità. Per contro, le tecniche di Raman coerente, come ad esempio la diffusione Raman Anti-Stokes coerente (CARS), sfruttando la nonlinearità dell’interazione tra luce di sonda e campione, permettono di superare i limiti sopra descritti, e per questa ragione sono ampiamente utilizzate nonostante la maggior complessità e il costo dell’apparato sperimentale. D’altronde, negli ultimi venti anni, la grande diffusione di oscillatori laser a impulsi ultracorti e la disponibilità di fibre a cristalli fotonici per la generazione di luce bianca coerente hanno facilitato lo sviluppo di microscopi CARS a bassa energia di eccitazione e tempi di acquisizione brevi, che sono di particolare utilità in campo biologico e biomedico. In questo rapporto tecnico, dopo un breve richiamo alle caratteristiche della spettroscopia CARS al femtosecondo, viene descritto il microspettrometro CARS realizzato nel C. R. Casaccia nell’ambito di un progetto ENEA inter-dipartimentale. Inoltre, vengono riportati e discussi i risultati sperimentali ottenuti durante i primi due anni di operatività del sistema.Raman spectroscopy allows the measurement of vibrational maps of samples with high spatial resolution, useful for the identification of chemical compounds without the use of labels. In general, however, spontaneous Raman techniques suffer from some disadvantages, mainly due to low signal levels and the possible presence of fluorescence signals, which can limit their applicability. On the other hand, coherent Raman techniques, such as Coherent Anti-Stokes Raman Scattering (CARS), exploiting the nonlinearity of the interaction between probe and sample light, permit to overcome the limits described above, and for this reason they are widely used despite the greater complexity and cost of the experimental apparatus. On the other hand, in the last twenty years, the great diffusion of ultrashort pulse laser oscillators and the availability of photonic crystal fibers for the generation of coherent white light have facilitated the development of CARS microscopes with low excitation energy and short acquisition times, which are particularly useful in the biological and biomedical fields. In this technical report, after a brief reference to the characteristics of the femtosecond CARS spectroscopy, the CARS microspectrometer made in C. R. Casaccia in the framework of an inter-departmental ENEA project is described. Furthermore, the experimental results obtained during the first two years of operation of the system are reported and discussed
Characterization of supercontinuum generation in a photonic crystal fiber for uses in multiplex CARS microspectroscopy
No full textCoherent anti-Stokes Raman scattering (CARS) is a versatile technique for vibrational imaging that can be realized by a simple setup using a single femtosecond laser oscillator. For such a layout, supercontinuum generation in a photonic crystal fiber (PCF) is commonly used to produce a broadband Stokes beam in the so-called multiplex CARS spectroscopy; accordingly, characterization of the supercontinuum beam is a necessary requirement to perform controlled experiments. In this paper, we first perform simulations and characterizations of the supercontinuum spectra produced by a PCF in conditions encountered in a typical single-oscillator multiplex CARS setup. Good agreement between the experimental and simulated supercontinuum spectra is obtained in the whole emission band and for different PCF working conditions, by accurate choice of the simulation input parameters and by accounting for the input beam chirp in the numerical code. The influence of PCF working conditions on the CARS signal measured on a reference sample is also shown. To this regard, we also study the long-term stability of the Stokes beam and of the associated CARS signal, using the Allan variance to determine a limit to the acquisition time in CARS measurements. We show that Stokes and CARS long-term spectral fluctuations are on a timescale of some minutes in our setup, setting an indicative limit to the practical acquisition time for reliable CARS measurements. Based on this work, good control over the measurement of vibrational bands by CARS microscopy can be achieved in view of optimized performances in specific spectral bands
Unraveling urban form and collision risk: The spatial distribution of traffic accidents in Zanjan, Iran
Full text linkOfficial statistics demonstrate the role of traffic accidents in the increasing number of fa-talities, especially in emerging countries. In recent decades, the rate of deaths and injuries caused by traffic accidents in Iran, a rapidly growing economy in the Middle East, has risen significantly with respect to that of neighboring countries. The present study illustrates an exploratory spatial analysis’ framework aimed at identifying and ranking hazardous locations for traffic accidents in Zanjan, one of the most populous and dense cities in Iran. This framework quantifies the spatiotem-poral association among collisions, by comparing the results of different approaches (including Kernel Density Estimation (KDE), Natural Breaks Classification (NBC), and Knox test). Based on descriptive statistics, five distance classes (2–26, 27–57, 58–105, 106–192, and 193–364 meters) were tested when predicting location of the nearest collision within the same temporal unit. The empirical results of our work demonstrate that the largest roads and intersections in Zanjan had a significantly higher frequency of traffic accidents than the other locations. A comparative analysis of distance bandwidths indicates that the first (2–26 m) class concentrated the most intense level of spatiotem-poral association among traffic accidents. Prevention (or reduction) of traffic accidents may benefit from automatic identification and classification of the most risky locations in urban areas. Thanks to the larger availability of open-access datasets reporting the location and characteristics of car accidents in both advanced countries and emerging economies, our study demonstrates the potential of an integrated analysis of the level of spatiotemporal association in traffic collisions over metropolitan regions
M-Branes on Minimal Surfaces
Full text linkWe construct some new brane solutions in M-theory, based on the minimal surfaces. In particular, we consider the anti-self-dual Nutku geometry, and embed it in the membranes and five-branes of the eleven-dimensional supergravity. We explicitly show that the solutions preserve eight supersymmetries. Upon compactification on a circle, we find fully localized intersecting brane systems. We also discuss the T-dual and the decoupling limits of the solutions.32 page
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Challenges in High-Fidelity Implicit Block-Based Numerical Simulation of Dynamic Out-of-Plane Two-Way Bending in Unreinforced Brick Masonry Walls
Full text linkThis study deals with the high-fidelity block-based finite element simulation of dynamic out-of-plane (OOP) responses of unreinforced masonry (URM) walls, explicitly focusing on two-way bending behaviors under seismic loads, which is a common critical failure mode in real-world masonry structures. While experimental shake-table tests provide valuable insights into these behaviors, their high costs, complexity, and limited scalability highlight the need for advanced numerical modeling approaches. A state-of-the-art block-based finite element modeling strategy that conceives masonry as an assemblage of 3D damaging blocks interacting via contact-based cohesive-frictional zero-thickness interfaces, previously proposed for simulating cyclic quasi-static and dynamic one-way bending tests, is here extended for the first time to the simulation of incremental dynamic shake-table tests on OOP two-way spanning URM full-scale walls, subjected to a sequence of dynamic loads. The numerical models track the reference experimental behaviors with high accuracy in terms of collapse onset, failure mechanism, experienced acceleration and displacements, and hysteretic response. The effects of variations in mechanical properties, boundary conditions, and damping on the dynamic response are explored in a sensitivity study. The results indicate that slight changes in these parameters can lead to considerable differences in outcomes. This highlights the chaotic nature of the dynamic response of masonry walls, especially in near-collapse conditions, which makes probabilistic approaches more suitable for predicting masonry OOP dynamics. The proposed numerical methodology appears compatible with statistical frameworks, given the limited costs with respect to experimental tests, and it extends knowledge beyond physical experiments
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
M-Theory Solutions and Intersecting D-Brane Systems
Full text linkIt is believed that fundamental M-theory in the low-energy limit can be described
effectively by D=11 supergravity.
Extending our understanding of the different classical brane solutions in M-theory
(or string theory) is important, and so there is a lot of interest in finding D=11
M-brane solutions such that after reduction to ten dimensions, they (or some combinations
of them) reduce simply to the supersymmetric BPS saturated p-brane solutions.
In this thesis, we study and construct M2 and M5-branes solutions in D=11
supergravity. The M-brane solutions are constructed by lifting a D-brane to a four
or higher dimensional geometry embedded in M-theory and then placing M-brane
solutions in the background geometry.
We present new analytic M2 and M5-brane solutions in M-theory based on transverse
Gibbons-Hawking and Bianchi spaces. These solutions provide realizations of
fully localized type IIA D2/D6 and NS5/D6 brane intersections. One novel feature
of these solutions is that the metric functions depend on more than two transverse
coordinates, unlike all the other previous known solutions. Moreover since the metric
functions in the Gibbons-Hawking geometries depends on more than one physical
parameters, their embedding into M-theory yield new M-brane solutions with the
M-brane metric functions depend on both compact and non-compact coordinates.
We show that all new solutions have eight preserved supersymmetries. Upon
reduction to 10 dimensions, we find that the world-volume theories of the NS5-branes
decouple from the bulk for these solutions
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