On the Effective Elastic Properties of Macroscopically Isotropic Media Containing Randomly Dispersed Spherical Particles

computational scheme for estimating the effective elastic properties of a particle reinforced matrix is investigated. The randomly distributed same-sized spherical particles are assumed to result in a composite material that is macroscopically isotropic. The scheme results in a computational efficient method to establish the correct bulk and shear moduli by representing the three-dimensional (3D) structure in a two-dimensional configuration. To this end, the statistically equivalent area fraction is defined in this work, which depends on two parameters: the particle volume fraction and the number of particles in the 3D volume element. We suggest that using the statistically equivalent area fraction,introduced and defined in this work, is an efficient way to obtain the effective elastic properties of an isotropic media containing randomly dispersed same-size spherical particles

Assessing Plastically Dissipated Energy as a Condition for Fatigue Crack Growth

The suitability of using a proposed condition for simulating cyclic crack propagation in a numerical scheme is qualitatively investigated, employing the finite element method. The propagation criterion is based on a condition that relates the plastically dissipated energy to a critical value. In the finite element simulation scheme, the crack is allowed to propagate when the criterion is satisfied, and the crack propagates until the condition is no longer fulfilled. Experimentally, it is well established that a negative load ratio increases the crack propagation rate, whereas a tensile overload tends to decrease the crack propagation rate. By simulating these load conditions, we show that the proposed propagation criterion closely captures these rate changes

A Simple Numerical Method of Cycle Jumps for Cyclically Loaded Structures

A method for accelerated numerical simulations of structures subjected to cyclic loading is investigated. Of particular interest is a class of structures where the structural properties evolve with time. The proposed method is based on conducting detailed finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FEA simulations. This includes a control function that automatically monitors the length of the cycle jump to ensure a realistic solution. We compare the proposed method to a reference calculation, where all incremental cycles are conducted, and find that the cycle jump solution replicates the true solution

An Object-Oriented Approach for Modeling and Simulation of Crack Growth in Cyclically Loaded Structures

We present an object-oriented modeling frame for simulating crack propagation due to cyclic loadings. Central to the approach is that the crack propagates when a user-defined propagation criterion is fulfilled, i.e., the crack propagation rate is not prescribed but predicted. The approach utilizes the commercial finite element software package ABAQUS and its associated Python based scripting interface. The crack propagation is simulated by a generalized node release technique. If the propagation criteria are satisfied in the end of a cycle, the crack is allowed to propagate. The incremental crack growth is inferred from an iterative investigation of the propagation criteria. The propagation criteria are user-defined, and can be based on any parameter or parameter set that can be obtained from the simulations. We illustrate the developed modeling frame by two benchmark problems, where the propagation criterion is based on the dissipated energy in the vicinity of the crack tip

The role of multimodal neuromonitoring during anesthesia for ablation of giant endocranial tumors

Catedra de anesteziologie și reanimatologie nr.2, Catedra de anesteziologie și reanimatologie nr.1 „Valeriu Ghereg”, Catedra de neurochirurgie, USMF „Nicolae Testemițanu”, Chișinău, Republica Moldova, Conferința stiințifică „Nicolae Anestiadi – nume etern al chirurgiei basarabene” consacrată centenarului de la nașterea profesorului Nicolae Anestiadi 26 august 2016Material şi metode. În studiu au fost incluse 2 loturi de pacienţi: I lot– 6 pacienţi cărora li s-a administrat anestezie combinată (i/v + pivot inhalator cu sevofluran); lotul II– 5 pacienţi cărora li s-a administrat anestezie totală intravenoasă (propofol+fentanil). Monitoring: TAs, TAd, TAm (invaziv), PVC, echilibru acidobazic, gazos (arteră şi venă periferică, bulbul jugular), electrolitic, acidul lactic, diurezei orară, PESS. Discuţii. În lotul pacienţilor cu anestezie inhalatorie s-a determinat o incidenţă înaltă a depresiei hemodinamice profunde (Tam - 74,3 mmHg, p= 0,02). Tot aici s-a determinat: utilizarea dozelor mai mici de analgetice şi miorelaxante (sol. atracurium bromid 0,35-0,4mg/kg) , trezire mai rapidă, incidenţă mai scăzută a greții şi tremorului postoperator. S-a reuşit efectuarea mai veridică a neuromonitorigului, datorită cantităţii mai mici de miorelaxante utilizate. La pacienţii cu anestezie intravenoasă s-a determinat o stabilitate hemodinamică (Tam - 82,7 mmHg, p ≤ 0,05), hemoragie intraoperatorie nesemnificativă. În lotul dat s-a reuşit efectuarea neuromonitorigului, cu doze obişnuite de miorelaxante (sol. atracurium bromid 0,5 mg/kg). Concluzii. Tehnicile descrise pot fi utilizate pentru neuromonitorizare multimodală în ablaţia de tumori endocraniene. Tehnica de anestezie inhalatorie, respectând farmacocinetica preparatelor, ar putea fi de preferat, din cauza evitării riscurilor de supra - sau sub dozare de medicamente anestezice, oferind o trezire mai rapidă, cu o evaluarea neurologică imediată, care este extrem de importantă.Materials and methods. The study included two groups of patients: I-st group - 6 patients receiving combined anesthesia (i / v + inhaled sevoflurane); II-nd group - 5 patients who received intravenous anesthesia (propofol + fentanyl).Monitoring: sBP, dBP, mBP (invasive), CVP, acid-base, gas (peripheral artery and vein, jugular bulb) and electrolytic balances, lactic acid, hourly diuresis, neurology evoked potentials. Discussion. In the group of patients with inhalation anesthesia was determined a higher incidence of hemodynamic depression (Tam - 74,3 mmHg, p= 0,02). Also it was determined: use of lower doses of analgetics and muscle relaxants (sol. atracurium bromid 0,35-0,4mg/kg), faster awakening, lower incidence of postoperative nausea and tremors. We managed a more accurate recording of evoked potentials due to the small amount of muscle relaxant used. In patients with intravenous anesthesia was determined a more stable BP (mBP - 82,7 mmHg, p ≤ 0,05), less intraoperative bleeding. In the group given was carrying neuromonitorigului managed with dose of muscle relaxant common (ground. atracurium aromide 0.5 mg / kg). Conclusions. The techniques described can be used for multimodal neuromonitoring in ablation of tumor endocranial. Inhalational anesthesia technique, respecting the pharmacokinetics preparations could be preferable because avoid the risks of over - or under dosage of anesthetic agents, providing an awakening faster with immediate neurological evaluation, which is extremely important

Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure

Effects of cold-rolling deformation on texture evolution and mechanical properties of Ti-29Nb-9Ta-10Zr alloy

International audienceThe crystallographic texture of Ti-29Nb-9Ta-10Zr alloy is studied after cold-rolling with different amounts of thickness reduction, up to 60%. The major texture components developed during cold-rolling were: γ-fibre components: {111}〈View the MathML source〉, {111}〈View the MathML source〉, {111}〈View the MathML source〉 and {111}〈View the MathML source〉; texture component: {112}〈View the MathML source〉 and texture components: {001}〈View the MathML source〉 and {010}〈001〉. Besides crystallographic texture the resulted mechanical properties were studied by nanoindentation. It was showed that the decrease in Young's modulus after different cold-rolling stages is mainly attributed to the stress-induced α″-Ti phase formation. At 60% cold-rolling thickness reduction obtained an elastic modulus close to 45.29±3.81 GPa, coupled with an average Vickers microhardness close to 279.83±4.28 HV

Acute kidney injury in patients with tetralogy of Fallot who have undergone surgical correction

Catedra de anesteziologie și reanimatologie nr.2, USMF „Nicolae Testemițanu”, Departamentul Reanimare și Terapie Intensivă, Spitalul Clinic Republican, Chișinău, Republica Moldova, Conferința stiințifică „Nicolae Anestiadi – nume etern al chirurgiei basarabene” consacrată centenarului de la nașterea profesorului Nicolae Anestiadi 26 august 2016Introducere. Leziunea renală acută (LRA) este una dintre cele mai frecvente și severe complicații în chirurgia cardiacă. Aplicarea criteriilor de clasificare RIFLE (risc, injurie, insuficiență și stadiul final al bolii renale) au fost validate la populațiile pediatrice. Scop. De a determina, retrospectiv apariția LRA în grupul de pacienți până la 18 ani, utilizând criteriile RIFLE modificate, validate la copii (pRIFLE), relația dintre LRA cu alte complicații după corecția chirurgicală a tetralogiei Fallot. Materiale și metode. Din baza de date a IMSP Spitalul Clinic Republican, au fost selectați 45 de copii, supuși corecției chirurgicale a tetralogiei Fallot între iunie 2010 și decembrie 2015. Leziunea renală acută a fost definită ca o scădere a cantității clearance-ului estimat al creatininei pe baza criteriilor pediatrice modificate pentru RIFLE (pRIFLE). Rezultate. Douăzeci și două de pacienți (48,9%) au avut LRA în funcție de categoriile pRIFLE. Dintre cei 45 pacienți, 15 (33,3%) au corespuns criteriilor pRIFLE de risc; 6 (13,3%) au atins criteriile de injurie și 1 (2,2%) au întrunit criteriile de insuficiență. Trei pacienți (6,7%) au decedat. Apariția MODS s-a întâlnit la 19 (42,2%) pacienți, sepsis s-a întîlnit la 3 (6,7%) pacienți. Durata de ventilație mecanică (p <0,001) și durata de ședere în unitatea de terapie intensivă ( p <0,001) au fost semnificativ mai mare în comparație cu grupul de pacienți care nu au dezvoltat semne de leziune renală acută. Concluzii. Disfuncția renală acută a fost asociată în mod independent, cu o apariție crescută a complicațiilor postoperatorii, dar cu o mortalitate redusă după corecția chirurgicală a tetralogiei Fallot.Introduction. Acute kidney injury (AKI) is one of the most common and severe complications in cardiac surgery. Application of the classification RIFLE (risk, injury, failure and end stage renal disease) have been validated in pediatric populations. Purpose. To determine AKI appearance in the patients up to 18 years, using modified RIFLE criteria, validated in children (pRIFLE), the relationship between AKI with other complications after surgical correction of Fallot's tetralogy. Materials and methods. From the database of the Republican Clinical Hospital, were selected 45 children undergoing surgical correction of Fallot's tetralogy between June 2010 and December 2015. acute kidney injury was defined as a decrease in estimated creatinine clearance based on criteria pediatric modified RIFLE (pRIFLE). Results. Twenty-two patients (48,9%) had AKI by pRIFLE category. Of the 45 patients, 15 (33.3%) met the criteria pRIFLE risk; 6 (13.3%) corresponded to the criteria of injury and one (2.2%) met criteria for failure. Three patients (6.7%) died. The occurrence of MODS was encountered in 19 (42.2%) patients, sepsis was met in 3 (6.7%) patients. Duration of mechanical ventilation (p <0.001) and length of stay in the intensive care unit p <0.001) were significantly higher compared with the group of patients who did not develop signs of acute kidney injury. Conclusions. Acute kidney dysfunction was independently associated with an increased occurrence of postoperative complications, but with reduced mortality after surgical correction of Fallot's tetralogy

Field Localization and Enhancement of Phase Locked Second and Third Harmonic Generation in Absorbing Semiconductor Cavities

We predict and experimentally observe the enhancement by three orders of magnitude of phase mismatched second and third harmonic generation in a GaAs cavity at 650nm and 433nm, respectively, well above the absorption edge. Phase locking between the pump and the harmonics changes the effective dispersion of the medium and inhibits absorption. Despite hostile conditions the harmonics become localized inside the cavity leading to relatively large conversion efficiencies. Field localization plays a pivotal role and ushers in a new class of semiconductor-based devices in the visible and UV ranges