A Unified Theoretical Description of the Thermodynamical Properties of Spin Crossover with Magnetic Interactions

After the discovery of the phenomena of light-induced excited spin state trapping (LIESST), the functional properties of metal complexes have been studied intensively. Among them, cooperative phenomena involving low spin-high spin (spin-crossover) transition and magnetic ordering have attracted interests, and it has become necessary to formulate a unified description of both phenomena. In this work, we propose a model in which they can be treated simultaneously by extending the Wajnflasz-Pick model including a magnetic interaction. We found that this new model is equivalent to Blume-Emery-Griffiths (BEG) Hamiltonian with degenerate levels. This model provides a unified description of the thermodynamic properties associated with various types of systems, such as spin-crossover (SC) solids and Prussian blue analogues (PBA). Here, the high spin fraction and the magnetization are the order parameters describing the cooperative phenomena of the model. We present several typical temperature dependences of the order parameters and we determine the phase diagram of the system using the mean-field theory and Monte Carlo simulations. We found that the magnetic interaction drives the SC transition leading to re-entrant magnetic and first-order SC transitions.Comment: 30pages, 11figure

Simple scoring system to predict in-hospital mortality after surgery for infective endocarditis

BACKGROUND: Aspecific scoring systems are used to predict the risk of death postsurgery in patients with infective endocarditis (IE). The purpose of the present study was both to analyze the risk factors for in-hospital death, which complicates surgery for IE, and to create a mortality risk score based on the results of this analysis. METHODS AND RESULTS: Outcomes of 361 consecutive patients (mean age, 59.1\ub115.4 years) who had undergone surgery for IE in 8 European centers of cardiac surgery were recorded prospectively, and a risk factor analysis (multivariable logistic regression) for in-hospital death was performed. The discriminatory power of a new predictive scoring system was assessed with the receiver operating characteristic curve analysis. Score validation procedures were carried out. Fifty-six (15.5%) patients died postsurgery. BMI >27 kg/m2 (odds ratio [OR], 1.79; P=0.049), estimated glomerular filtration rate 55 mm Hg (OR, 1.78; P=0.032), and critical state (OR, 2.37; P=0.017) were independent predictors of in-hospital death. A scoring system was devised to predict in-hospital death postsurgery for IE (area under the receiver operating characteristic curve, 0.780; 95% CI, 0.734-0.822). The score performed better than 5 of 6 scoring systems for in-hospital death after cardiac surgery that were considered. CONCLUSIONS: A simple scoring system based on risk factors for in-hospital death was specifically created to predict mortality risk postsurgery in patients with IE

Ultrafast, broadband and tunable terahertz reflector and neutral density filter based on high resistivity silicon

We report THz transmission and reflection properties of an ultrafast optically excited highly resistive silicon wafer. Amplified Ti:Sapphire femtosecond laser pulses at 800 nm were used to create fluence-dependent carrier density on the front surface of the wafer which modifies the dielectric properties at the THz frequencies. Time-resolved experiments in the optical pump-THz probe configuration were conducted in which THz pulses reflected off from the surface at 0°and 45°angles of incidence make it possible to measure the pump-fluence dependent ultrafast evolution of the reflection and transmission coefficients in 0.5-6 THz range. An analytical model, where both the Drude contributions from the photoexcited electrons and holes account for the change of the dielectric constant of the photoexcited silicon, has been used to evaluate the THz reflection and transmission coefficients at steady state. Thus obtained results match well with the experimental results and demonstrate an all-optical means to convert a silicon wafer into an ultrafast, tunable and broadband neutral density filter or reflector in the THz frequency range

Study of femtosecond laser-induced grating in lead silicate glasses

Summary form only given. In previous studies, we have shown that the grating photo-induced by femtosecond laser pulses in a SF59 lead silica glass is not formed instantaneous and continues to evolve at the millisecond time scales after excitation. The grating reflectivity was shown to depend on the pump power density and on the number of exciting pulses [1]. The grating was directly written onto the SF glasses by imaging a master grating, which is illuminated by femtosecond laser pulses (1mJ, ~50fs, 1KHz, ~800nm) [2]. The formation of the grating was shown to result from defects photo-induced by the two photon-absorption of the femtosecond laser pulses [1,2]. Theses defects induce a change of the real (Δnr) and imaginary (Δni) part of refractive index of the glass. However our previous experiments were not able to reveal the time scale for the formation of these defects or to evidence the impact of the two photons absorption on Δnr or Δni. Indeed for a given laser power density, one expects to observe an increase of Δnr and therefore of the grating reflectivity as two-photon absorption coefficient α2 is increased. To evidence the time scale for the formation of these defects, we have measured the evolution of the reflectivity of the photo-induced grating on the picoseconds time scale. As shown in Fig.1a, we found that depending on the pump power density, a rapid growth of the reflectivity is recorded in about 1.5ps to 4ps (Fig.1a). In a good agreement with the formation of the effects in glasses, this indicates that photo-induced defects are produced on few picoseconds [3]. Now Δnr should depends on the number of defects Ndef induced by two-photon absorption: The higher the α2 of the glass, the higher Ndef and the larger (Δnr). In lead silica glasses α2 is linearly proportional to the PbO molar density [4]. This phenomenon is related to the shift of the edge absorption band of the glass toward the longer wavelength with the PbO glass content (Fig.1b). As expected, Fig.1c indicates that, at 1 kHz femtosecond pulse repetition rate and for moderate power density, Δnr increases linearly with PbO molar fraction. Moreover, as the power density is further increased, we notice that Δnr saturate. The value of Δnr at saturation depends on and increases with PbO molar density. The ensemble of measurements that contributes to the understanding of the index modification of glasses photo-induced by femtosecond pulses will be discussed in more details during our presentation

Nuclear and electronic contributions to the third-order nonlinearity in different glasses

Using, a time resolved optical heterodyne Kerr effect experiment along with a Raman light diffusion experiment, we have measured the nuclear (non-instantaneous) and electronic (instantaneous) contributions to the nonlinear index of refraction in tellurite niobium-doped and silicate lead-doped glasses. The experimental set-up and the procedure used to measure the nuclear and electronic contribution are detailed. Our experimental results clearly indicate that the ratio between the instantaneous and the non-instantaneous contribution remain constant while the doping concentration or the temperature of the sample vary. These ratios are ˜5 and ˜10 in tellurite niobium-doped and silicate lead glasses, respectively

INTERPRETATION OF THE ANOMALOUS CRITICAL-BEHAVIOR IN A QUATERNARY MICROEMULSION

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INTERPRETATION OF THE ANOMALOUS CRITICAL-BEHAVIOR IN A QUATERNARY MICROEMULSION

no abstrac