1,721,043 research outputs found
Coarsening and metastability of the long-range voter model in three dimensions
No full textWe study analytically the ordering kinetics and the final metastable states in the three-dimensional long-range voter model where N agents described by a boolean spin variable S-i can be found in two states (or opinion) +/- 1. The kinetics is such that each agent copies the opinion of another at distance r chosen with probability P(r) proportional to r(-alpha) (a > 0). In the thermodynamic limit N ->infinity the system approaches a correlated metastable state without consensus, namely without full spin alignment. In such states the equal-time correlation function C(r) = < SiSj > (where r is the i-j distance) decrease algebraically in a slow, non-integrable way. Specifically, we find C(r) similar to r(-1), or C(r)similar to r(6-a), or C(r)similar to r(-a) for a >5, 3< a <= 5 and 0 <= <= a <= 3, respectively. In a finite system metastability is escaped after a time of order N and full ordering is eventually achieved. The dynamics leading to metastability is of the coarsening type, with an ever increasing correlation length L(t) (for N ->infinity). We find L(t)similar to t1/2 for a <= 5 L(t)similar to t5{2\al}}4<\al \le 53\le \al \le 40\le \al < 3$ there is not macroscopic coarsening because stationarity is reached in a microscopic time. Such results allow us to conjecture the behavior of the model for generic space dimension
Ordering kinetics with long-range interactions: interpolating between voter and Ising models
No full textWe study the ordering kinetics of a generalization of the voter model with long-range interactions, the p-voter model, in one dimension. It is defined in terms of Boolean variables S-i, agents or spins, located on sites i of a lattice, each of which takes in an elementary move the state of the majority of p other agents at distances r chosen with probability P(r)proportional to r(-alpha). For p = 2 the model can be exactly mapped onto the case with p = 1, which amounts to the voter model with long-range interactions decaying algebraically. For 3 <= p < infinity, instead, the dynamics falls into the universality class of the one-dimensional Ising model with long-ranged coupling constant J(r) = P(r) quenched to small finite temperatures. In the limit p -> infinity, a crossover to the (different) behavior of the long-range Ising model quenched to zero temperature is observed. Since for p > 3 a closed set of differential equations cannot be found, we employed numerical simulations to address this case
Exploring professionals’ motivation to lead: a cross-level study in the healthcare sector
No full textThe extant leadership research has paid increasing attention to the concept of motivation to lead (MTL) as an individual construct that strongly affects leadership processes and behaviors. However, despite its importance, scant knowledge is available about how individual characteristics and organizational structural features interact in influencing MTL in professional-based organizations. This article contributes to this line of research by adopting a multilevel perspective to study the MTL among individual professionals in the healthcare sector. We collected data from a sample of 791 physicians nested in 44 departments belonging to 27 hospitals. Using the hierarchical linear model, we tested the impact of individual and organizational variables on the motivation of physicians to engage in managerial positions. Our findings demonstrate that the physicians' MTL was positively associated with their individual self-efficacy. Departmental decentralization interacted with this self-efficacy, such that the effect of self-efficacy on the MTL was significantly lower when decentralization was high. We discuss the implications of these findings for human resource management and organizational (re)design within professional organizations
Parts-per-billion detection of carbon monoxide: A comparison between quartz-enhanced photoacoustic and photothermal spectroscopy
Full text linkWe report on a comparison between two optical detection techniques, one based on a Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) detection module, where a quartz tuning fork is acoustically coupled with a pair of millimeter-sized resonator tubes; and the other one based on a Photothermal Spectroscopy (PTS) module where a Fabry-Perot interferometer acts as transducer to probe refractive index variations. When resonant optical absorption of modulated light occurs in a gas sample, QEPAS directly detects acoustic waves while PTS probes refractive index variations caused by local heating. Compact QEPAS and PTS detection modules were realized and integrated in a gas sensor system for detection of carbon monoxide (CO), targeting the fundamental band at 4.6 μm by using a distributed-feedback quantum cascade laser. Performance was compared and ultimate detection limits up to ∼ 6 part-per-billion (ppb) and ∼15 ppb were reached for QEPAS and the PTS module, respectively, using 100 s integration time and 40 mW of laser power
Light-induced thermo-elastic effect in quartz tuning forks exploited as a photodetector in gas absorption spectroscopy
Full text linkWe report on a study of light-induced thermo-elastic effects occurring in quartz tuning forks (QTFs) when exploited as near-infrared light detectors in a tunable diode laser absorption spectroscopy sensor setup. Our analysis showed that when the residual laser beam transmitted by the absorption cell is focused on the QTF surface area where the maximum strain field occurs, the QTF signal-to-noise ratio (SNR) is proportional to the strain itself and to the QTF accumulation time. The SNR was also evaluated when the pressure surrounding the QTF was lowered from 700 Torr to 5 Torr, resulting in an enhancement factor of v4 at the lowest pressure. At 5 torr, the QTF employed as light detector showed an SNR v6.5 times higher than that obtained by using a commercially available amplified photodetector
High and flat spectral responsivity of quartz tuning fork used as infrared photodetector in tunable diode laser spectroscopy
Full text linkInfrared laser technology over the last decades has led to an increasing demand for optical detectors with high sensitivity and a wide operative spectral range suitable for spectroscopic applications. In this work, we report on the performance of a custom quartz tuning fork used as a sensitive and broadband infrared photodetector for absorption spectroscopy. The photodetection process is based on light impacting on the tuning fork and creating a local temperature increase that generates a strain field. This light-induced, thermoelastic conversion produces an electrical signal proportional to the absorbed light intensity due to quartz piezoelectricity. A finite-element-method analysis was used to relate the energy release with the induced thermal distribution. To efficiently exploit the photo-induced thermoelastic effects in the low-absorbance spectral region of quartz also, chromium/gold layers, acting as opaque surface, have been deposited on the quartz surface. To demonstrate the flat response as photodetectors, a custom tuning fork, having a fundamental resonance frequency of 9.78 kHz and quality factor of 11 500 at atmospheric pressure, was employed as photodetector in a tunable diode laser absorption spectroscopy setup and tested with five different lasers with emission wavelength in the 1.65-10.34 μm range. A spectrally flat responsivity of ∼2.2 kV/W was demonstrated, corresponding to a noise-equivalent power of 1.5 nW/Hz, without employing any thermoelectrical cooling systems. Finally, a heterodyne detection scheme was implemented in the tunable diode laser absorption spectroscopy setup to retrieve the resonance properties of the quartz tuning fork together with the gas concentration in a single, fast measurement
Photoacoustic spectroscopy for gas sensing: A comparison between piezoelectric and interferometric readout in custom quartz tuning forks
Full text linkWe report on a comparison between piezoelectric and interferometric readouts of vibrations in quartz tuning forks (QTFs) when acting as sound wave transducers in a quartz-enhanced photoacoustic setup (QEPAS) for trace gas detection. A theoretical model relating the prong vibration amplitude with the QTF prong sizes and electrical resistance is proposed. To compare interferometric and piezoelectric readouts, two QTFs have been selected; a tuning fork with rectangular-shape of the prongs, having a resonance frequency of 3.4 kHz and a quality-factor of 4,000, and a QTF with prong having a T-shape characterized by a resonance frequency of 12.4 kHz with a quality-factor of 15,000. Comparison between the interferometric and piezoelectric readouts were performed by using both QTFs in a QEPAS sensor setup for water vapor detection. We demonstrated that the QTF geometry can be properly designed to enhance the signal from a specific readout mode
Mid-Infrared Quartz-Enhanced Photoacoustic Sensor for ppb-Level CO Detection in a SF6Gas Matrix Exploiting a T-Grooved Quartz Tuning Fork
No full textAn optical sensor for highly sensitive detection of carbon monoxide (CO) in sulfur hexafluoride (SF6) was demonstrated by using the quartz-enhanced photoacoustic spectroscopy technique. A spectrophone composed of a custom 8 kHz T-shaped quartz tuning fork with grooved prongs and a pair of resonator tubes, to amplify the laser-induced acoustic waves, was designed aiming to maximize the CO photoacoustic response in SF6. A theoretical analysis and an experimental investigation of the influence of SF6 gas matrix on spectrophone resonance properties for CO detection have been provided, and the performances were compared with the standard air matrix. A mid-infrared quantum cascade laser with a central wavelength at 4.61 μm, resonant with the fundamental band of CO, and an optical power of 20 mW was employed as the light excitation source. A minimum detection limit of 10 ppb at 10 s of integration time was achieved, and a sensor response time of ∼3 min was measured
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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